Bypass Record
AMSI Bypass × Microsoft Windows Defender
A publicly-reported instance of AMSI Bypass bypassing Microsoft Windows Defender, recorded with its original source. Factual record; no assessment of any specific deployment.
Mechanism
The tool manually loads PE files into memory, parses EAT to find function addresses, and hooks AmsiScanBuffer via absolute EAT hooking to return AMSI_RESULT_CLEAN. This prevents Defender from detecting malicious memory operations. LSASS dumping uses a callback to MiniDumpWriteDump with NULL file handle, encrypting and storing the dump in memory.
Detection & mitigation
Monitor for suspicious modifications to the AMSI AmsiScanBuffer function in memory, such as inline hooks or IAT/EAT patching, using endpoint detection tools that track integrity of security-related DLLs. Deploy AMSI provider integrity checks and enable Windows Defender Attack Surface Reduction rules to block tampering attempts.
This is a record of a publicly-reported event, not an assessment of any specific organization's deployment. Detection and mitigation notes are drawn from the cited source. Where the source is silent, fields are omitted.