Callstack Spoofing + Indirect Syscalls POC – Unmasking Evasion Techniques In A Proof Of Concept (POC) Scenario

This project consists of a simple C++ self-Injecting dropper focused on EDR evasion POC. To implement it, I have combined the use of Windows Thread Pooling to hide the call stack and the use of indirect syscalls to avoid hooking in the NTDLL.

As can be seen in the images, from the Cordyceps code, it performs a jump to ntdll to utilize one of the syscall instructions. This should be considered a malicious action; however, upon executing the return in ntdll, we return to the code of tpWorker, which is located within ntdll. Thus, from the perspective of the antivirus (AV), ntdll would appear to be making a call to another part of ntdll, which is not considered malicious.

Future Upgrades:

Implement a mechanism to automatically search for the syscall number.
In-memory payload decryption.

To compile:

nasm -f win64 ./syscalls.asm -o ./syscalls.obj
g++ -o cordyceps.exe main.cpp syscalls.obj

Varshini

Varshini is a Cyber Security expert in Threat Analysis, Vulnerability Assessment, and Research. Passionate about staying ahead of emerging Threats and Technologies.