A PowerShell AMSI Bypass technique via Vectored Exception Handler (VEH). This technique does not perform assembly instruction patching, function hooking or Import Address Table (IAT) modification.
For this technique to work, you must first inject the VEH DLL into the PowerShell process. This can be done either by injecting the DLL or via DLL hijacking .
This technique works by setting up a hardware breakpoint on the function AmsiScanBuffer on all PowerShell process threads, then installing a VEH to handle the trigger of this breakpoint.
When a thread calls AmsiScanBuffer, the VEH will make the thread to exit the function without executing anything and setting the result of the function to AMSI_RESULT_CLEAN. This is all done inside the VEH, without modifying the code of the process or without any PE modifications.
For demonstration purposes, this repository contains a very basic DLL injector. Use it this way:
- 1.) Compile the DLL Injector and VEH DLL.
- 2.) Open an instance of PowerShell.
- 3.) Run the DLL injector by providing the FULL PATH to the DLL. Example:
./DLL_Injector.exe C:\Windows\Temp\AMSI_VEH.DLL- 4.) PowerShell will open a MessageBox window to confirm the VEH installation.
This repository is for academic purposes, the use of this software is your responsibility.