Potential PowerShell Obfuscation Via Reversed Commands — Sigma Rule

Rule metadata and linked tags

Author: Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton. Source status: test; severity: high. Source dates: 2020-10-11 / 2023-05-31.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 818ee3163046778cad6f1cbab391361d9c4bdefbfd514db08896b614e2f01794

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 Obfuscation Via Reversed Commands
id: b6b49cd1-34d6-4ead-b1bf-176e9edba9a4
status: test
description: Detects the presence of reversed PowerShell commands in the CommandLine. This is often used as a method of obfuscation by attackers
references:
    - https://2019.offzone.moscow/ru/report/hunting-for-powershell-abuses/
    - https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=66
author: Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton
date: 2020-10-11
modified: 2023-05-31
tags:
    - attack.stealth
    - attack.t1027
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_cli:
        CommandLine|contains:
            - 'hctac'
            - 'kaerb'
            - 'dnammoc'
            - 'ekovn' # Also covers 'ekovni'
            - 'eliFd'
            - 'rahc'
            - 'etirw'
            - 'golon'
            - 'tninon'
            - 'eddih'
            - 'tpircS'
            - 'ssecorp'
            - 'llehsrewop'
            - 'esnopser'
            - 'daolnwod'
            - 'tneilCbeW'
            - 'tneilc'
            - 'ptth'
            - 'elifotevas'
            - '46esab'
            - 'htaPpmeTteG'
            - 'tcejbO'
            - 'maerts'
            - 'hcaerof'
            - 'retupmoc'
    filter_main_encoded_keyword:
        # We exclude usage of encoded commands as they might generate FPs as shown here:
        #   https://github.com/SigmaHQ/sigma/pull/2720
        #   https://github.com/SigmaHQ/sigma/issues/4270
        CommandLine|contains:
            - ' -EncodedCommand '
            - ' -enc '
    condition: all of selection_* and not 1 of filter_main_*
falsepositives:
    - Unlikely
level: high

Original YAML and metadata in JSON

False positives

• Unlikely

Source references

• https://2019.offzone.moscow/ru/report/hunting-for-powershell-abuses/
• https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=66