huntrule

Windows: .NET Reflection Attempt to Disable AMSI via amsiInitFailed

Alerts on Windows command lines referencing amsiInitFailed and .NET reflection patterns to disable AMSI scanning.

FreeReviewedSigma · High · v1
Product
windows
Category
process_creation
Author
Markus Neis, @Kostastsale (SigmaHQ), DRL 1.1
Published
2018-08-17
Updated
2026-07-30
AnalysisDetection

ATT&CK techniques

  1. Recon

  2. Resource Dev

  3. Initial Access

  4. Execution

  5. Persistence

  6. Priv Esc

  7. Defense Evasion

  8. Cred Access

  9. Discovery

  10. Lateral Movement

  11. Collection

  12. C2

  13. Exfiltration

  14. Impact

What it detects

This rule flags process creation events where the command line references PowerShell AMSI utilities and specifically the string "amsiInitFailed". It also matches .NET reflection usage patterns that set a non-public static value to $null/$true, which can be used to impair AMSI scanning. The detection relies on Windows process command-line telemetry and string matches within the PowerShell/.NET invocation.

Reporting behind it

Related detections9 linkedT1685 — drag to rearrange
Malicious Microsoft Defender Disabled via Registry DisableAntiSpyware (via process_creation)
Suspicious Termination of Defender Tray Process via Taskkill
Malicious Windows Defender Disablement via MpCmdRun RemoveDefinitions
Malicious Unsigned VIB Installation on ESXi Host via esxcli (via process_creation)
Suspicious In-Memory PowerShell Execution from Web Server via Automation Assembly (via image_load)
Malicious EDR Evasion Driver Load from AnyDesk Directory via k.sys (via image_load)
Malicious Zemana Vulnerable Driver Load for EDR Termination (via image_load)
Suspicious EDRKillShifter Vulnerable Driver Load from User Temp Directory (via image_load)
Malicious AuKill EDR Killer Kernel Driver Load via Process Explorer Driver (via image_load)
Windows: .NET Reflection Attempt to Disable AMSI via amsiInitFailed
Pivot detection · T1685 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.