EDRStartupHinder Tool Blocks Antivirus on Windows Defender

This week, security researcher TwoSevenOneT unveiled EDRStartupHinder. The researcher is notable for creating other EDR evasion tools, including EDR-Freeze and EDR-Redir.

The tool blocks antivirus and EDR services at startup by redirecting critical System32 DLLs via Windows Bindlink, demonstrated on Windows Defender in Windows 11 25H2.​

Antivirus and EDR services operate like standard Windows services but with enhanced protection from kernel drivers.

They run under SYSTEM privileges, auto-start on boot, and use Protected Process Light (PPL) to prevent user-mode tampering. Configuration changes in user mode fail, and processes resist modification without advanced techniques such as EDR-Freeze.

Bindlink Startup Disruption

Previous techniques, like EDR-Redir, redirected EDR folders post-startup, but vendors hardened against them. EDRStartupHinder preempts this by targeting System32, which is essential for all processes, including EDRs.

Steps include creating a higher-priority service, Bindlinking a core DLL to an unsigned “corrupted” copy, leveraging PPL to crash the EDR on load failure, and cleaning up post-termination.

Service priority draws from BYOVD research, checking HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlServiceGroupOrder. The DLL must avoid the KnownDLLs preload list, identifiable via Process Monitor.

Available on GitHub, EDRStartupHinder takes parameters: OriginalLib (System32 DLL), FakeLib (copy location), ServiceName/Group (priority), EDRProcess (target like MsMpEng.exe).

It corrupts the PE header signature on FakeLib, registers as service, monitors for EDR launch, applies/removes Bindlink dynamically. Users must research EDR-specific DLLs and groups using Process Explorer boot logs.​

On a lab Windows 11 25H2 system, targeting MsMpEng.exe (Defender engine) and msvcp_win.dll (loaded at startup), with TDI service group priority. Command: EDRStartupHinder.exe msvcp_win.dll C:TMPFakeLib DusmSVC-01 TDI MsMpEng.exe.

Post-reboot, the service activates first, redirects DLL; PPL-protected MsMpEng rejects the unsigned DLL and self-terminates.

Sysadmins should monitor bindlink.dll usage, suspicious services in high-priority groups, and System32 anomalies. Defense-in-depth includes KnownDLL expansions, signature enforcement audits, and minifilter logging. Vendors must harden DLL dependencies and startup sequencing.​

This technique underscores Windows mechanisms as double-edged swords for red teams, effective against Defender and unnamed commercial EDRs/AVs in labs.

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