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ByePg: Defeating Patchguard using Exception-hooking

ByePg hijacks the HalPrivateDispatchTable table to create a early-bugcheck hook. Utilizing this early-bugcheck hook it collects information about the exception and basically provides a simple interface to register a high-level system-wide exception handler.

A variety of kernel hooks can be implemented using this method completely bypassing PatchGuard and HVCI as it creates an entirely new attack surface, exception-based hooking, which was previously not possible in Windows kernel.

Writeup:

https://blog.can.ac/2019/10/19/byepg-defeating-patchguard-using-exception-hooking/

Project Structure:

  • \ByePgLib contains the base library
  • \ExHook contains a standalone SYSCALL hooking example using ByePg
  • \ExceptionHookingDemo demonstrates the exception handler
  • \InfinityHookFix contains a sample rendering the recent InfinityHook patch by Microsoft useless
  • \FreeSeh contains a SEH-via-ByePg module letting you use SEH in manual mapped images bypassing PatchGuard's inverted function table checks

Result:

ExHook

P.S.

There are many other things that can be done using the base library and many things can be improved, be SEH handling or BugCheck parsing, so I would really appreciate any form of contribution to this repo.