LJP-TW/Windows-Pwn-Step-by-Step

Let's get familiar with Windows pwn 😎

Windows Pwn Step-by-Step

• Intro
• Environment
• Tools
• ExploitMe_1
• Reference

Intro

In Linux pwn, I often need to debug dynamically between chal and exploit script

The steps are：

1. Add a raw_input('>') to exploit python script
2. Run exploit script
3. Find out chal process pid
   • Linux
     • pidof chal
   • Windows
     • Use tools (e.g. 火絨劍, Process Explorer)
4. Attach debugger to this process with the pid
   • Linux
     • gdb at $(pidof chal)
   • Windows
     • Use tools (e.g. WinDbg)
5. The debugger stops at internal of something like read() of standard lib
   • Windows
     • There are many threads in process, and debugger may not stop at the thread executing read()
     • Switch to this thread with command like ~0s
6. Input finish (command of gdb), until the process return to some function like main()
   • Windows WinDbg
     • Shift + F11
7. Check whether my exploit script writes bytes to memeory correctly
   • gdb
     • x/10xg $ebp-0x20
   • WinDbg
     • d @esp-0x20

Check out ExploitMe Demo ;)

Environment

Version 1909 (OS Build 18363.657)

Tools

pwintools

Basic pwntools for Windows written in python 2.7

Deps

• PythonForWindows

  git clone https://github.com/hakril/PythonForWindows.git
  python setup.py install
  

• capstone

  pip install capstone
  

Install

git clone https://github.com/masthoon/pwintools.git

• Revise setup.py from

  install_requires=[
      'PythonForWindows==0.4',
  ],
  

  to

  install_requires=[
      'PythonForWindows==0.5',
  ],
  

python setup.py

WinDbg

Install WinDbg Preview in Microsoft $tore

ncat

ncat is part of nmap

Install nmap

ROPgadget

Install ROPgadget

pip install ropgadget

The path is C:\Python27\Scripts\ROPgadget

火絨劍

You can use other process explorer tools as a alter

• 火絨劍: http://bbs.huorong.cn/thread-7800-1-1.html

PE-bear

Install PE-bear

ExploitMe_1

ExploitMe_1.exe is a simple program with buffer overflow vuln

This is a similar example of this book, at page 89

The book also teaches you to build shellcode ;)

Disable mitigation

• Disable DEP Set VS2019 project property
  • Linker
    • Advanced
      • Data Execution Prevention (DEP): No (/NXCOMPAT:NO)
• Disable GS Set VS2019 project property
  • Configuration Properties
    • C/C++
      • Code Generation
        • Security Check: Disable Security Check (/GS-)
• Disable ASLR Run setting.bat

Demo

First, let's disable ASLR

.\setting.bat

Debug

1. Edit exploit.py Add raw_input('>') at line7

2. Run exploit.py

3. Find pid In this demo, it's 3168

4. Attach to this process with WinDbg

   • Check Show processes from all users

   

   

   • command k: Display the stack frame

     • There is no something like main

   • command ~: See a list of all threads

     • Switch to thread 0: ~0s
     • Display the stack frame again
     • ExploitMe_1!main+0x4d that's what I want to see!

5. Return to main

   • Shift + F11 WinDbg is stuck, waiting for input
   • Press Enter at exploit
   • Shift + F11 until return to main

6. Check memory

7. Continue process

   • F10

Find gadget

1. Use ROPgadget to find gadgets in kernel32.dll

   • In this demo we disable ASLR, so we can use gadget in dll

   python \Python27\Scripts\ROPgadget --binary \Windows\SysWoW64\kernel32.dll > gadget
   

2. Find push esp ; ret

   0x6b86ade5 : push esp ; ret
   

3. Find Image base of \Windows\SysWoW64\kernel32.dll

   • Use PE-bear
   • Find out the Image base is 0x6b800000
   • So the offset of push esp ; ret gadget is 0x6b86ade5 - 0x6b800000 = 0x6ade5

4. Do the steps of debug to step 5 again

   • Then find out the where Kernel32 starts
   • command lm: List modules
   • Find out the base is 0x76f70000
   • So the gadget address is 0x76f70000 + 0x6ade5 = 0x76fdade5

5. Check gadget

   • Remember to revise exploit script

Pwn

Reference

• Modern Windows Exploit Development
• https://stackoverflow.com/questions/4946685/good-tutorial-for-windbg

tags: security