Obex, a newly released proof-of-concept utility by security researcher dis0rder0x00, demonstrates a simple but effective user-mode method to stop unwanted security and monitoring modules from loading into Windows processes.
The tool launches a target process under debugger control and enforces a configurable DLL blocklist, preventing both startup and runtime loads of designated libraries.
A demonstration shows Obex spawning PowerShell while ensuring amsi.dll is never mapped, highlighting practical bypass potential against in-process inspection.
Upon invocation, Obex parses its command-line arguments to identify the target executable and an optional comma-separated list of DLL names to block.
If no list is provided, it defaults to preventing the Antimalware Scan Interface library from loading into the new process.
Obex then creates the child process in a debug state, allowing it to intercept module load notifications immediately during process initialization.
Whenever the debug API reports an impending module load be it a startup dependency or a dynamic LoadLibrary call Obex compares the DLL name in a case-insensitive fashion against its blocklist.
If there is a match, Obex suppresses the load request, causing the module to remain absent from the process’s address space.
The child process continues execution without the blocked libraries, and Obex logs or reports the blocked events for operator visibility.
Key Features of Obex
Obex stands out for its minimalism and flexibility through several core capabilities:
- Process Debug Control: Spawns any process with arguments under debug control, enabling early interception of module loads
- Configurable DLL Blocking: Blocks a customizable list of DLLs by name, allowing targeted prevention of specific security modules
- Dual-Phase Protection: Works for both startup DLLs loaded during process initialization and dynamically loaded DLLs via LoadLibrary functions
- Zero Dependencies: Written in plain C with no external dependencies, ensuring minimal footprint and easy deployment
- Case-Insensitive Matching: DLL names are matched without regard to case, improving reliability across different naming conventions
- Default Blocklist: Automatically blocks amsi.dll when no custom DLL list is provided, immediately demonstrating EDR bypass capabilities
- Real-time Blocking: Intercepts and prevents module loads in real-time during process execution
- Verification Support: Provides clear evidence of blocked modules through process module enumeration
Obex reveals that defenders relying solely on user-mode hooks or mandatory in-process inspection can be selectively blinded when attackers control process launch parameters.
By preventing specified DLLs from loading, adversaries can evade telemetry and undermine detection rules that depend on those modules.
Kernel-mode protections, such as enforcing library load integrity at a lower level or hardening AMSI integrations, offer more resilient defenses.
EDR vendors should also validate behavior when core components are missing and escalate integrity alerts accordingly.
Obex serves as a timely reminder that defense-in-depth must extend beyond user-mode instrumentation to reliably maintain visibility and control.
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