PowerShell Base64 Encoded Invoke Keyword — Sigma Rule

Rule metadata and linked tags

Author: pH-T (Nextron Systems), Harjot Singh, @cyb3rjy0t. Source status: test; severity: high. Source dates: 2022-05-20 / 2023-04-06.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: e6ad822eccdf3f7c3f0b6f6244251cbc2d8570ccb94ed02f1134c0fbc43b46be

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: PowerShell Base64 Encoded Invoke Keyword
id: 6385697e-9f1b-40bd-8817-f4a91f40508e
related:
    - id: fd6e2919-3936-40c9-99db-0aa922c356f7
      type: obsolete
status: test
description: Detects UTF-8 and UTF-16 Base64 encoded powershell 'Invoke-' calls
references:
    - https://thedfirreport.com/2022/05/09/seo-poisoning-a-gootloader-story/
author: pH-T (Nextron Systems), Harjot Singh, @cyb3rjy0t
date: 2022-05-20
modified: 2023-04-06
tags:
    - attack.execution
    - attack.stealth
    - attack.t1059.001
    - attack.t1027
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_cli_enc:
        CommandLine|contains: ' -e'
    selection_cli_invoke:
        CommandLine|contains:
            # Invoke-
            # UTF-16LE
            - 'SQBuAHYAbwBrAGUALQ'
            - 'kAbgB2AG8AawBlAC0A'
            - 'JAG4AdgBvAGsAZQAtA'
            # UTF-8
            - 'SW52b2tlL'
            - 'ludm9rZS'
            - 'JbnZva2Ut'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high
simulation:
    - type: atomic red team
      name: Create a Process using WMI Query and an Encoded Command
      technique: T1047
      atomic_guid: 7db7a7f9-9531-4840-9b30-46220135441c
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_powershell_base64_invoke/info.yml

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://thedfirreport.com/2022/05/09/seo-poisoning-a-gootloader-story/