AMSI Bypass Pattern Assembly GetType — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: high. Source dates: 2022-11-09 / not supplied.

{
  "product": "windows",
  "category": "ps_script",
  "definition": "Requirements: Script Block Logging must be enabled"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: db8c99ec1d92ccc85eb20937601127d60e14b5801c1d7ce31d246cb35e3d8f85

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: AMSI Bypass Pattern Assembly GetType
id: e0d6c087-2d1c-47fd-8799-3904103c5a98
status: test
description: Detects code fragments found in small and obfuscated AMSI bypass PowerShell scripts
references:
    - https://www.mdsec.co.uk/2018/06/exploring-powershell-amsi-and-logging-evasion/
    - https://twitter.com/cyb3rops/status/1588574518057979905?s=20&t=A7hh93ONM7ni1Rj1jO5OaA
author: Florian Roth (Nextron Systems)
date: 2022-11-09
tags:
    - attack.defense-impairment
    - attack.t1685
    - attack.execution
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection:
        ScriptBlockText|contains|all:
            - '[Ref].Assembly.GetType'
            - 'SetValue($null,$true)'
            - 'NonPublic,Static'
    condition: selection
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://www.mdsec.co.uk/2018/06/exploring-powershell-amsi-and-logging-evasion/
• https://twitter.com/cyb3rops/status/1588574518057979905?s=20&t=A7hh93ONM7ni1Rj1jO5OaA