Reversing Tools Basic Methods

Reversing Tools & Basic Methods

This skill provides guidance on reverse engineering tools and methodologies for various platforms, languages, and binary formats.

Quick Reference by Target Type

.NET Decompilation & Debugging

Tool Selection

• dotPeek (JetBrains): Best for examining .dll, .winmd, .exe files. Can save as Visual Studio project.
• ILSpy: Cross-platform, has VSCode extension. Good for quick decompilation.
• dnSpy/dnSpyEx: Use when you need to decompile, modify, and recompile. Right-click → "Modify Method" to edit functions.

Debugging .NET Applications

To debug a .NET application with dnSpy:

1. Modify assembly attributes to enable debugging:

   // Change from:
   [assembly: Debuggable(DebuggableAttribute.DebuggingModes.IgnoreSymbolStoreSequencePoints)]
   
   // To:
   [assembly: Debuggable(DebuggableAttribute.DebuggingModes.Default |
       DebuggableAttribute.DebuggingModes.DisableOptimizations |
       DebuggableAttribute.DebuggingModes.IgnoreSymbolStoreSequencePoints |
       DebuggableAttribute.DebuggingModes.EnableEditAndContinue)]
   

2. Compile and save the modified module via File → Save module...

3. If running under IIS, restart with:

   iisreset /noforce
   

4. Attach debugger:

   • Close all opened files in dnSpy
   • Debug Tab → Attach to Process...
   • Select w3wp.exe (IIS worker process)
   • Click Attach

5. Load modules:

   • Debug → Break All
   • Debug → Windows → Modules
   • Click any module → Open All Modules
   • Right-click in Assembly Explorer → Sort Assemblies

Adding Logging in dnSpy

To make dnSpy log information to a file, insert this code:

using System.IO;
path = "C:\\inetpub\\temp\\MyTest2.txt";
File.AppendAllText(path, "Password: " + password + "\n");

Shellcode Analysis & Debugging

Tool Selection

Debugging with Blobrunner

1. Run Blobrunner with your shellcode
2. It will allocate the shellcode in memory and stop execution
3. Note the memory address where shellcode was allocated
4. Attach debugger (IDA or x64dbg) to the process
5. Set breakpoint at the indicated address
6. Resume execution to debug the shellcode

Debugging with jmp2it

1. Run jmp2it with your shellcode
2. It allocates shellcode and starts an eternal loop
3. Attach debugger to the process
4. Play start, wait 2-5 seconds, press stop
5. You'll be in the eternal loop
6. Jump to next instruction (call to shellcode)
7. Now executing the shellcode

Using scdbg

# Get basic info
scdbg.exe -f shellcode

# Show analysis report at end
scdbg.exe -f shellcode -r

# Enable interactive hooks (file/network) + report
scdbg.exe -f shellcode -i -r

# Dump decoded shellcode
scdbg.exe -f shellcode -d

# Find where shellcode starts
scdbg.exe -f shellcode /findsc

# Start execution at specific offset
scdbg.exe -f shellcode /foff 0x0000004D

Key features:

• Tells you which functions the shellcode uses
• Detects if shellcode is self-decoding in memory
• Create Dump option saves decoded shellcode if modified dynamically
• Start offset to begin at specific location

Using Cutter

1. Open Cutter (GUI for radare2)
2. Open File or Open Shellcode
3. Set a breakpoint where you want to start emulation
4. Cutter will automatically start emulation from there
5. View stack in hex dump

Disassembling with CyberChef

Upload shellcode file and use this recipe:

• To Hex (Space separator)
• Disassemble x86 (32-bit, Full x86 architecture)

DLL Debugging

Using x64dbg/x32dbg

1. Load rundll32.exe:

   • 64-bit: C:\Windows\System32\rundll32.exe
   • 32-bit: C:\Windows\SysWOW64\rundll32.exe

2. Change Command Line (File → Change Command Line):

   "C:\Windows\SysWOW64\rundll32.exe" "path\to\your.dll",FunctionName
   

3. Configure settings:

   • Options → Settings
   • Select "DLL Entry"

4. Start execution - debugger will stop at each DLL entry point

5. When stopped in your DLL's entry, search for breakpoints

Tip: When execution stops, check the top of x64dbg window to see which code you're in.

Using IDA

1. Load rundll32.exe
2. Select Windbg debugger
3. Select "Suspend on library load/unload"
4. Configure execution parameters with DLL path and function name
5. Start debugging - execution stops when each DLL loads

Wasm Decompilation

Online Tools

• wasm2wat: https://webassembly.github.io/wabt/demo/wasm2wat/index.html
  • Decompiles from wasm (binary) to wat (text)
• wat2wasm: https://webassembly.github.io/wabt/demo/wat2wasm/
  • Compiles from wat to wasm
• web-wasmdec: https://wwwg.github.io/web-wasmdec/
  • Alternative decompiler

Software Tools

• Jeb: https://www.pnfsoftware.com/jeb/demo
• wasmdec: https://github.com/wwwg/wasmdec

Platform-Specific Tools

Rust Binaries

1. Search for functions containing ::main
2. Identify the main function (often obvious from binary name)
3. Search function names online to learn about inputs/outputs

Delphi Binaries

1. Use IDR: https://github.com/crypto2020/IDR
2. Use IDA-For-Delphi plugin: https://github.com/Coldzer0/IDA-For-Delphi
3. In IDA, press ALT+F7 to import Python plugin
4. Select the plugin and start debugging
5. Press Start button (green or F9) - breakpoint hits at real code start
6. Pressing buttons in GUI will stop debugger in executed function

Golang Binaries

1. Use IDAGolangHelper plugin: https://github.com/sibears/IDAGolangHelper
2. In IDA, press ALT+F7 to import Python plugin
3. Select the plugin to resolve function names

GBA Games

Tools:

• no$gba (debug version): GUI debugger with interface
• mgba: CLI debugger
• gba-ghidra-loader: Ghidra plugin
• GhidraGBA: Ghidra plugin

Key Input Values:

A = 1
B = 2
SELECT = 4
START = 8
RIGHT = 16
LEFT = 32
UP = 64
DOWN = 128
R = 256
L = 512

Common Pattern:

• Address 0x4000130 contains KEYINPUT function
• Look for how program treats user input
• Check for button value comparisons in decompiled code

Game Boy

Reference: https://www.youtube.com/watch?v=VVbRe7wr3G4

Obfuscation Handling

Movfuscator

What it does: Modifies all instructions to mov and uses interrupts to change execution flow.

Deobfuscation:

1. Try demovfuscator: https://github.com/kirschju/demovfuscator

2. Install dependencies:

   apt-get install libcapstone-dev
   apt-get install libz3-dev
   

3. Install Keystone:

   apt-get install cmake
   mkdir build && cd build
   ../make-share.sh
   make install
   

4. CTF workaround: https://dustri.org/b/defeating-the-recons-movfuscator-crackme.html

GUI Apps & Games

• Cheat Engine: Find and modify values in running game memory
• PiNCE: GDB front-end focused on games, works for any reverse engineering
• Decompiler Explorer (dogbolt.org): Compare decompiler outputs on small executables

Compiled Python

To extract Python code from ELF/EXE compiled binaries, use standard .pyc extraction methods.

Learning Resources

• Z0F Course: https://github.com/0xZ0F/Z0FCourse_ReverseEngineering
• ABD (Binary Deobfuscation): https://github.com/malrev/ABD

Workflow Recommendations

Before Starting

1. Identify the target type (language, platform, format)
2. Select appropriate tools from the tables above
3. Check for obfuscation (movfuscator, custom packers)
4. Set up debugging environment (disable optimizations if needed)

During Analysis

1. Start with static analysis (decompile, disassemble)
2. Move to dynamic analysis (debug, trace execution)
3. Document findings (function names, key addresses, logic flow)
4. Test hypotheses (modify code, recompile, verify)

Common Pitfalls

• Optimizations prevent breakpoints: Modify assembly attributes for .NET
• Shellcode self-decoding: Use scdbg to dump decoded version
• Missing function names: Use language-specific IDA plugins
• Wrong architecture: Verify 32-bit vs 64-bit before loading

Quick Commands Reference

# .NET IIS restart
iisreset /noforce

# scdbg analysis
scdbg.exe -f shellcode -r
scdbg.exe -f shellcode -d

# Install demovfuscator deps
apt-get install libcapstone-dev libz3-dev cmake

When to Use This Skill

Use this skill when you need to:

• Decompile or analyze compiled binaries
• Debug shellcode or malicious payloads
• Reverse engineer .NET, Java, Golang, Delphi, or Rust applications
• Work with Wasm, GBA games, or other specialized formats
• Handle obfuscated binaries
• Select appropriate tools for a reverse engineering task
• Understand debugging workflows for different platforms