A new proof-of-concept (PoC) tool named Obex has been released, offering a method to prevent Endpoint Detection and Response (EDR) and other monitoring solutions’ dynamic-link libraries (DLLs) from loading into processes.
The tool, created by a researcher known as “dis0rder0x00,” is designed to block specified DLLs both during the initial startup of a process and at runtime, potentially allowing malware or red team tools to operate without being detected by security software.
Obex functions by launching a target application under its debug control. This allows it to intercept critical system operations. Specifically, it hooks the ntdll!LdrLoadDll function, which is responsible for loading DLLs into a process.
When an application attempts to load a DLL, Obex intercepts the call and checks the DLL’s name against a configurable blocklist.
If the DLL is on the list, the tool simulates a failed load attempt, preventing the library from being injected into the process.
If the DLL is not on the list, the loading process is allowed to continue as normal. This technique effectively blinds security tools that rely on injecting their own DLLs into processes to monitor their behavior.
The tool is written in C and has no external dependencies, making it lightweight and portable. By default, Obex is configured to block amsi.dll, the library for the Antimalware Scan Interface, but users can provide a custom list of DLLs to block.
The developer has made the tool available on GitHub, positioning it as a technique for security researchers to understand and test evasion methods.
Security solutions widely use DLL injection to establish user-mode hooks for monitoring API calls and system behavior. Tools like Obex demonstrate methods that can be used to circumvent these defenses.
While valuable for penetration testers and red teams, such tools also provide defenders and security vendors with important insights into evasion techniques, helping them to develop more resilient detection and protection strategies against sophisticated threats.
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