Sigma rule: Potential AMSI Bypass Via .NET Reflection

A detection rule from the SigmaHQ repository, shown as its author published it. Dataset version ref-c28bce8a2311, updated 2023-02-03T00:00:00.000Z.

Rule

Title
Potential AMSI Bypass Via .NET Reflection
Status
test
Level
high
Author
Markus Neis, @Kostastsale
Date
2018-08-17
Modified
2023-02-03
File
rules/windows/process_creation/proc_creation_win_powershell_amsi_init_failed_bypass.yml
Commit
ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects Request to "amsiInitFailed" that can be used to disable AMSI Scanning

Log source

product
windows
category
process_creation

Detection

selection:
    - CommandLine|contains|all:
          - 'System.Management.Automation.AmsiUtils'
          - 'amsiInitFailed'
    - CommandLine|contains|all:
          - '[Ref].Assembly.GetType'
          - 'SetValue($null,$true)'
          - 'NonPublic,Static'
condition: selection

False positives (as the rule lists them)

  • Unlikely

Tags

  • attack.defense-impairment
  • attack.t1685

MITRE ATT&CK ids this rule names

Related rules

References

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/process_creation/proc_creation_win_powershell_amsi_init_failed_bypass.yml

Sources and licences

  • SigmaHQ

    "Potential AMSI Bypass Via .NET Reflection" by Markus Neis, @Kostastsale (SigmaHQ). Rule: https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules/windows/process_creation/proc_creation_win_powershell_amsi_init_failed_bypass.yml.
    Licensed under the Detection Rule License (DRL) 1.1: https://github.com/SigmaHQ/Detection-Rule-License

    Detection Rule License (DRL) 1.1

Cite this page

Dragons Eye Ransomware Tracker, "Sigma rule: Potential AMSI Bypass Via .NET Reflection",
entity page, dataset version ref-c28bce8a2311, updated 2023-02-03T00:00:00.000Z,
https://ransomware-tracker.com/detections/sigma/30edb182-aa75-42c0-b0a9-e998bb29067c (accessed 2026-11-03).
Underlying source: SigmaHQ rule 30edb182-aa75-42c0-b0a9-e998bb29067c, commit ccbb0369507f796db0b0ae6854c8a2be471b9d84.

Pages change. The dataset version identifies the data, but no archive of old versions is kept, so this citation cannot be replayed later.