Theory: EDR Syscall Hooking And Ghost Hunting, My Approach To Detection

(Recommended reading — you should read all the entries of the blog)

You Should Know:

1. Understanding EDR Syscall Hooking

EDRs (Endpoint Detection and Response) often use syscall hooking to monitor malicious activities. Attackers bypass these hooks using direct syscalls or unhooking techniques.

Key Commands & Techniques:

Check hooked syscalls on Windows:

Get-NtSyscall -Module "ntdll.dll" | Where-Object { $_.Hooked -eq $true }

Detect EDR hooks using SysWhispers3 (for direct syscall execution):

git clone https://github.com/klezVirus/SysWhispers3
python3 syswhispers.py --preset all -o syscalls

2. Ghost Hunting: Detecting Hidden Malware

Ghost hunting involves identifying stealthy malware that evades traditional detection.

Linux Memory Analysis with Volatility:

vol.py -f memory.dump linux_pslist  List processes 
vol.py -f memory.dump linux_check_syscall  Detect syscall table hooks

Windows Detection (via API Monitoring):

(Get-Process).Modules | Where-Object { $_.FileName -match "edr" }

3. Bypassing EDR with Rust (Rust-Based Evasion)

Rust allows low-level control, useful for crafting stealthy payloads.

Example Rust Syscall Execution:

use winapi::um::winnt::SYSCALL_ENTRY; 
unsafe { 
let syscall = get_syscall("NtAllocateVirtualMemory"); 
syscall(..); 
}

Threat Hunting with YARA & Sigma Rules

YARA Rule for Hook Detection:

rule edr_hook { 
strings: $hook = { 48 89 5C 24 ?? 57 48 83 EC 20 48 8B F9 } 
condition: $hook 
}

Sigma Rule for Unusual Syscall Activity:

title: Unusual Direct Syscall Execution 
detection: 
syscall: </li>
<li>"NtCreateThreadEx" </li>
<li>"NtWriteVirtualMemory" 
condition: selection

What Undercode Say:

EDR evasion is a cat-and-mouse game. Understanding syscall mechanics, memory forensics, and low-level programming is crucial for both attackers and defenders. Tools like SysWhispers, Volatility, and YARA help in analyzing and bypassing security mechanisms. Always test in controlled environments before real-world deployment.