🔬 Red Team & Evasion Techniques
Obex Exposed: The Defender's Guide to Detecting Runtime EDR Hooks and Dynamic Library Disabling
By CyberDudeBivash • October 02, 2025 • Technical Analysis
Disclosure: This is an advanced technical analysis for security researchers, EDR engineers, and threat hunters. It contains affiliate links to relevant security solutions and training. Your support helps fund our independent research.
Chapter 1: The EDR Arms Race — An Introduction to API Hooking and Evasion
Modern Endpoint Detection and Response (EDR) solutions are the cornerstone of security visibility. To see what a process is doing, they employ a technique called **API hooking**. In simple terms, when an EDR agent starts, it injects its own code into all running processes. It then modifies the first few bytes of critical functions in system libraries (like `ntdll.dll` or `kernel32.dll`) with a jump instruction that points to its own analysis code. When an application tries to, for example, create a new process by calling `CreateProcessW`, it first hits the EDR's hook. The EDR inspects the call, logs it, and then passes execution to the original function.
This is a powerful mechanism, but it is also a single point of failure. Sophisticated attackers and red teamers do not try to fight the EDR; they try to blind it. EDR evasion techniques are designed to tamper with or bypass these hooks, creating a blind spot where the malware can operate with impunity.
Chapter 2: Threat Analysis — A Technical Breakdown of the 'Obex' Unhooking Technique
The "Obex" technique is a form of dynamic, in-memory "unhooking." It assumes the attacker has already gained code execution on the endpoint, even as a low-privileged user.
The Unhooking Process:
- Map a Clean Copy:** The malware's first step is to get a "clean", unhooked version of a critical DLL to use as a reference. It does this by creating a file mapping of the legitimate DLL on disk (e.g., `C:\Windows\System32\ntdll.dll`) and mapping it into its own process's memory as a read-only data section.
- **Identify the Hooks:** The malware now has two versions of `ntdll.dll` in its memory: the one that was loaded normally by Windows (which has been hooked by the EDR) and its own clean, read-only copy. It then programmatically walks the export address table of both loaded modules and compares the first few bytes of each function (`NtCreateProcess`, `NtOpenFile`, etc.). Where there is a mismatch, it has found an EDR hook.
- **Perform the Unhook:** For each hooked function it finds, the malware uses the `VirtualProtect` Windows API call to change the memory permissions of the hooked function from Read & Execute to Read-Write-Execute.
- **Restore the Original Code:** The malware then copies the original, clean bytes from its read-only reference copy of the DLL over the top of the EDR's hook in the running code. The hook is now gone.
- **Operate with Impunity:** The malware can now call the unhooked functions (`NtCreateProcess`, `NtOpenFile`, etc.) from within its own process, and the EDR's user-mode sensor will be completely blind to these actions.
Chapter 3: The Defender's Playbook — How to Hunt for EDR Tampering
Defending against EDR evasion is a complex task that falls to both the EDR vendors and the security teams using the tools.
Vendor-Side Defenses:
- **Self-Protection:** Mature EDRs have robust self-protection mechanisms built into their kernel drivers to prevent tampering with their processes and hooks.
- **Kernel-Level Telemetry:** This is the most important defense. A modern EDR does not rely solely on user-mode hooks. It also has a kernel-mode driver that collects telemetry at a much lower, more privileged level. Even if an attacker unhooks `ntdll.dll` in their user-mode process, the kernel-mode driver can still see the resulting kernel-level events.
SOC Team / Hunter's Playbook:
You can proactively hunt for the act of unhooking itself:
- Hunt for `VirtualProtect` Abuse:** The `VirtualProtect` API call is the key to the attack. Create EDR queries to hunt for any process that calls `VirtualProtect` with `PAGE_EXECUTE_READWRITE` permissions on a memory segment belonging to a core system DLL like `ntdll.dll`. This is highly anomalous behavior.
- - **Hunt for Suspicious File Mapping:** Look for processes that create file mappings for core system DLLs. While sometimes legitimate, this can be an indicator of an unhooking attempt in progress.
👉 Defeating evasive threats requires an EDR/XDR platform that provides multi-layered visibility. A solution like **Kaspersky XDR** excels by correlating weak signals from user-mode, the kernel, and the network to build a high-confidence picture of an attack, even if one sensor is partially blinded.
Chapter 4: The Strategic Response — The Future of Endpoint Visibility
The constant arms race around user-mode hooking is driving a strategic shift in endpoint security. While user-mode hooks are still valuable, the industry is moving towards a greater reliance on more resilient, kernel-level data sources.
On Linux, this is the rise of **eBPF (extended Berkeley Packet Filter)**, which provides a safe and efficient way to instrument the kernel itself. On Windows, it involves leveraging the rich telemetry available from kernel-mode drivers and Event Tracing for Windows (ETW). A resilient EDR is one that assumes its user-mode sensors will be attacked and has redundant, deeper visibility sources to fall back on. As a security leader, when evaluating **Enterprise Security Solutions**, a key question for any EDR vendor must be: "What is your defense against runtime unhooking?"
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About the Author
CyberDudeBivash is a cybersecurity strategist with 15+ years in malware analysis, reverse engineering, and EDR evasion techniques, advising CISOs and security vendors across APAC. [Last Updated: October 02, 2025]
#CyberDudeBivash #EDREvasion #APIHooking #Malware #CyberSecurity #ThreatHunting #InfoSec #RedTeam #ThreatIntel
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