Evasion Of EDR: How One Security Researcher Turned Confusion Into Code + Video

Introduction:

In the perpetual arms race between attackers and defenders, understanding the mechanics of Endpoint Detection and Response (EDR) systems is the holy grail for penetration testers and malware developers. While many practitioners rely on automated tools to bypass security controls, a deeper comprehension of Windows internals, kernel callbacks, and Event Tracing for Windows (ETW) separates script kiddies from elite operators. This article deconstructs the journey of mastering EDR evasion, translating complex internals into actionable offensive security tradecraft.

Learning Objectives:

Understand the architecture of EDR sensors, including user-mode hooks and kernel-mode callbacks.
Learn to identify and analyze ETW providers for defensive telemetry.
Master the practical use of C and Assembly to manipulate Windows internals for evasion.
Develop a methodology to test EDR blind spots using custom tooling.

You Should Know:

1. Deconstructing the EDR Sensor: User-Mode Hooks

Most EDR solutions inject a DLL into user-mode processes to hook critical Windows APIs (e.g., NtCreateProcess, NtOpenProcess). These hooks redirect execution to the EDR’s inspection engine before the system call reaches the kernel.

Step‑by‑step guide to inspecting hooks:

Tooling: Use WinDbg or API Monitor to inspect loaded modules in a target process (e.g., notepad.exe).
Identify Hooks: Run the following command in an elevated PowerShell session to list modules loaded by a process and look for suspicious EDR-related DLLs:
```
Get-Process -Name "notepad" | Select-Object -ExpandProperty Modules | Where-Object {$<em>.ModuleName -like "edr" -or $</em>.ModuleName -like "hook"}
```
Disassembly Analysis: Open the target process in x64dbg (Windows). Navigate to a function like NtReadVirtualMemory. If the first few bytes are a `jmp` instruction (opcode 0xE9), it indicates a hook redirecting to the EDR’s inspection function. Note the destination address to map it back to the EDR DLL.

2. Kernel Callbacks: The EDR’s Rootkit-Like Visibility

EDRs register kernel callbacks to receive notifications for process creation, thread creation, and image loading. These callbacks operate at a higher privilege level than user-mode hooks and are significantly harder to blind.

Step‑by‑step guide to enumerating registered callbacks:

Tooling: Use NirSoft’s RegDllView or a custom WinDbg script.
WinDbg Kernel Debugging: Attach a kernel debugger to a test VM and run:
```
!process 0 0
!thread
```
(To find specific callback arrays, you must analyze the `PspCreateProcessNotifyRoutine` array.)
PowerShell (Living off the Land): While direct enumeration is restricted, you can use FLARE VM and run Sysinternal’s WinObj to explore the `\Callback` object manager namespace, though EDR callbacks are usually stored in undisclosed kernel structures.

4. Tool-Based Enumeration: Use NtObjectManager PowerShell module:

 Install the module if not present
Install-Module -Name NtObjectManager -Force
 Get all callback objects (requires SYSTEM integrity)
Get-NtObject \Callback -Recurse

3. ETW Threat Intelligence: The Silent Data Leak

Event Tracing for Windows (ETW) is the primary source of telemetry for modern EDRs. Microsoft Defender for Endpoint, SentinelOne, and CrowdStrike all rely on specific ETW providers (like Microsoft-Windows-Threat-Intelligence) to monitor for suspicious activity.

Step‑by‑step guide to monitoring and disabling ETW:

Enumerate Providers: Run logman to query active ETW sessions:
```
logman query -ets
```

Deep Provider Inspection: Use PowerShell to view registered providers and their GUIDs:

List all providers and their GUIDs
Get-WinEvent -ListProvider  | Select-Object Name, GUID | Out-GridView

Patching ETW in Memory: To blind EDR telemetry, attackers often patch the `ntdll!EtwEventWrite` function to return early (a no-op).

C Code Concept (for educational purposes):

// Find the address of EtwEventWrite in ntdll.dll
// Change memory protection (VirtualProtect) to PAGE_READWRITE
// Write 'ret' instruction (opcode 0xC3) to the first byte
// Restore original protection

Note: Modern EDRs monitor for patches to EtwEventWrite, making direct patching a high-risk action.

4. Memory Scanning: How EDRs Find Your Shellcode

EDRs scan the memory of processes for known malicious signatures (byte patterns) or anomalous permissions (e.g., PAGE_EXECUTE_READWRITE). This is why simply allocating memory with `VirtualAllocEx` and writing shellcode is often detected.

Step‑by‑step guide to evading memory scanning:

Allocate with different permissions: Allocate memory as PAGE_READWRITE, write your encrypted shellcode, then change permissions to `PAGE_EXECUTE_READ` (using VirtualProtectEx) right before execution.
Spawn-Safe Process: Create a sacrificial process (like rundll32.exe) in a suspended state, inject your shellcode into it, and then resume it.

PowerShell PoC (simulating injection flow):

$proc = Start-Process -FilePath "C:\Windows\System32\rundll32.exe" -PassThru -WindowStyle Hidden
 Allocate memory in remote process (p/invoke required, not pure PS)
 Write shellcode
 Change memory protection to Execute
 Create remote thread to execute

5. Blind Spots: Callback Derealization and Unhooking

EDRs cannot monitor what they cannot see. By loading a fresh copy of `ntdll.dll` from disk into memory (overwriting the hooked section), an attacker can remove user-mode hooks.

Step‑by‑step guide to unhooking ntdll:

Get a clean mapped image: Read `C:\Windows\System32\ntdll.dll` into memory.
Parse PE headers: Find the `.text` section of the freshly loaded copy.
Overwrite the hooked section: Use `WriteProcessMemory` to write the clean `.text` section over the hooked one in the current process.
Verification: Run a hook detection tool to confirm the `jmp` instructions are gone.
Building a Custom Loader in C (MalDev Principles)
Understanding EDR requires building your own tools. A basic loader that implements direct system calls (Syscalls) bypasses user-mode hooks entirely by invoking kernel routines directly from assembly.

Step‑by‑step guide (Conceptual Assembly):

Retrieve Syscall Numbers: Syscall numbers change per Windows version. They must be dynamically resolved by reading the `ntdll.dll` at runtime.
Assembly Stub: Write a small assembly routine that moves the syscall number into the `eax` register and executes the `syscall` instruction.

NASM Example for `NtAllocateVirtualMemory`:

section .text
global NtAllocateVirtualMemory
NtAllocateVirtualMemory:
mov r10, rcx
mov eax, 18h ; Syscall number for NtAllocateVirtualMemory (varies)
syscall
ret

3. C Integration: Call this assembly stub directly from your C code instead of calling the hooked ntdll!NtAllocateVirtualMemory.

What Undercode Say:

Internals Over Tools: Keith Monroe’s journey highlights a critical truth: mastery of Windows internals (kernel callbacks, ETW, memory management) yields more reliable evasion techniques than any off-the-shelf exploit generator. The ability to read disassembly and understand the C behind the hook is the new baseline for advanced persistence.
The Cat and Mouse Game: While EDRs have evolved to use kernel callbacks and memory scanning, their reliance on user-mode hooks and predictable ETW providers remains a structural weakness. The techniques discussed—from unhooking to direct syscalls—exploit the fundamental design of Windows rather than simple signature flaws, making them harder to patch without breaking system functionality.

Prediction:

As EDRs increasingly pivot to kernel-based telemetry and AI-driven behavioral analysis, the future of evasion will lie in “callback deregisration” (removing kernel callbacks) and exploiting hardware-level telemetry gaps. Expect a surge in research around eBPF for Windows and the weaponization of undocumented kernel structures to blind sensors at the source, forcing a new arms race in the Windows kernel itself.

▶️ Related Video (86% Match):

🎯Let’s Practice For Free:

IT/Security Reporter URL:

Reported By: Keith Monroe – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

🔐JOIN OUR CYBER WORLD [ CVE News • HackMonitor • UndercodeNews ]

💬 Whatsapp | 💬 Telegram

📢 Follow UndercodeTesting & Stay Tuned:

𝕏 formerly Twitter 🐦 | @ Threads | 🔗 Linkedin | 🦋BlueSky

Listen to this Post