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What is this?

NOTE: This tool is designed to parse and execute malicious payloads. Please take the necessary precautions and only use this tool in a controlled environment like a sandbox or a Virtual Machine

JITM is an automated tool to bypass the JIT Hooking protection on a .NET sample. JIT Hooking is the technique where the sample hooks the compileMethod() function. With the hook in place, the sample can easily replace the MSIL with a decrypted/deobfuscated version at run time. This makes static analysis almost impossible.

One possible solution is to install our own hook before loading the sample. We can have a chance to save/recover the real MSIL and save the content to a file. We can then rebuild the .NET executable by adding a brand new section containing the dumped methods and fix all methods in the MethodDef tables of the .NET #~ stream. The end result is still not runable without further intervention; however, it should be good enough to perform advanced static analysis.

How do I use this?

  • Make sure your sample is runable. If not, you may have to modify the tool
  • Run jitm sample.exe [optional_timeout_in_miliseconds]. jitm will first loads jitmhook.dll and calls HookNative() export to install a native hook. jitm then loads and run the sample entry point and wait for the timeout to expire before exiting. This should produces a jitm.log and jitm.json
  • Run the fix_assembly.py script: py -2 fix_assembly.py -f sample.exe -o output.exe -j jitm.json.
  • Use de4dot and dnSpy to statically analyze output.exe. However, to use a debugger, load and debug sample.exe instead.

Known issues

  • jitmhook saves both the MSIL and the method body header as tested on a variant of MassLogger. Future variants may change this behavior
  • Current python scripts only run on Python 2.7

How to build

Build and install PolyHook_2_0

Recommendation: use vcpkg method, and build statically to have all dependencies included in one DLL

git clone https://github.com/Microsoft/vcpkg.git
cd vcpkg
.\bootstrap-vcpkg.bat -disableMetrics
(as admin) .\vcpkg integrate install
vcpkg install polyhook2:x64-windows-static polyhook2:x86-windows-static

Build JITM

Open the sln file using Visual Studio 2017 or Visual Studio 2019 and build using the GUI.