Cyber security

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.

Recent Posts

What I Wish I Knew Before Learning Malware Analysis and Reverse Engineering

When I first started learning malware analysis and reverse engineering, I thought the hardest part…

3 days ago

git fetch vs git pull: How They Work and When to Use Each

Both git fetch and git pull talk to a remote repository, but they do very different things to your…

2 weeks ago

git cherry-pick Command: Apply Commits from Another Branch

Sometimes the change you need already exists, just on the wrong branch. A hotfix lands…

2 weeks ago

Best Email APIs for Secure Business Email: Why Developers Are Moving Beyond SMTP

Email is still one of the most important communication channels inside modern applications. Password resets,…

2 weeks ago

Nginx Commands in Linux: Start, Stop, Reload, Test, and Log

Nginx is a high-performance web server and reverse proxy trusted by some of the largest…

2 weeks ago

ufw Command in Linux: Manage Firewall Rules with Examples

ufw (Uncomplicated Firewall) sits on top of iptables (or nftables on newer systems) and replaces…

2 weeks ago