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
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Malicious Defender Disable And Executable Exclusion Via Registry
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Malicious AMSI and ETW Patching via PowerShell Script
Malicious PowMix AMSI Bypass via amsiInitFailed
Suspicious ThrottleStop Driver Abuse for Defense Evasion in Ransomware Attacks
Malicious Disabling of Microsoft Defender Real-Time Protection via SystemSettingsAdminFlows by DeadLock Ransomware
Suspicious Security Software Uninstallation via WMIC Product Call Uninstall (Chaos Ransomware)
Suspicious Security Product Uninstall via wmic product call uninstall
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.