Potential PowerShell Command Line Obfuscation — Sigma Rule

Rule metadata and linked tags

Author: Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton (fp). Source status: test; severity: high. Source dates: 2020-10-15 / 2024-04-15.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: f0d498c97c676400730442fd44eb2f3cbc5a8241dc88453f916e0e7c0da6f9e3

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: Potential PowerShell Command Line Obfuscation
id: d7bcd677-645d-4691-a8d4-7a5602b780d1
status: test
description: Detects the PowerShell command lines with special characters
references:
    - https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=64
author: Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton (fp)
date: 2020-10-15
modified: 2024-04-15
tags:
    - attack.execution
    - attack.stealth
    - attack.t1027
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_re:
        # TODO: Optimize for PySIGMA
        - CommandLine|re: '\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+'
        - CommandLine|re: '\{.*\{.*\{.*\{.*\{.*\{.*\{.*\{.*\{.*\{'
        - CommandLine|re: '\^.*\^.*\^.*\^.*\^'
        - CommandLine|re: '`.*`.*`.*`.*`'
    filter_optional_amazonSSM:
        ParentImage: C:\Program Files\Amazon\SSM\ssm-document-worker.exe
    filter_optional_defender_atp:
        CommandLine|contains:
            - 'new EventSource("Microsoft.Windows.Sense.Client.Management"'
            - 'public static extern bool InstallELAMCertificateInfo(SafeFileHandle handle);'
    condition: all of selection_* and not 1 of filter_optional_*
falsepositives:
    - Amazon SSM Document Worker
    - Windows Defender ATP
level: high

Original YAML and metadata in JSON

False positives

• Amazon SSM Document Worker
• Windows Defender ATP

Source references

• https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=64