AMSI Fail-Open Bypass via pAppName Null Write (Marshal.WriteInt64 amsiContext)

Ibrahim Saud@tektrix

•updated Jun 29, 2026•0•0•1

Detects attempts to bypass the Antimalware Scan Interface (AMSI) by nulling the pAppName pointer in memory using Marshal.WriteInt64. This technique forces AmsiScanBuffer and AmsiNotifyOperation to return E_INVALIDARG, causing them to fail open and skip security inspection.