Malicious Base64 Encoded PowerShell Keywords in Command Lines — Sigma Rule

Rule metadata and linked tags

Author: John Lambert (rule). Source status: test; severity: high. Source dates: 2019-01-16 / 2023-01-05.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: b4d024a513d7af863cdad4bdabe0855005de1a1a8cc5cdd41e134a71f0ee7f8d

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: Malicious Base64 Encoded PowerShell Keywords in Command Lines
id: f26c6093-6f14-4b12-800f-0fcb46f5ffd0
status: test
description: Detects base64 encoded strings used in hidden malicious PowerShell command lines
references:
    - http://www.leeholmes.com/blog/2017/09/21/searching-for-content-in-base-64-strings/
author: John Lambert (rule)
date: 2019-01-16
modified: 2023-01-05
tags:
    - 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_hidden:
        CommandLine|contains: ' hidden '
    selection_encoded:
        CommandLine|contains:
            - 'AGkAdABzAGEAZABtAGkAbgAgAC8AdAByAGEAbgBzAGYAZQByA'
            - 'aXRzYWRtaW4gL3RyYW5zZmVy'
            - 'IAaQB0AHMAYQBkAG0AaQBuACAALwB0AHIAYQBuAHMAZgBlAHIA'
            - 'JpdHNhZG1pbiAvdHJhbnNmZX'
            - 'YgBpAHQAcwBhAGQAbQBpAG4AIAAvAHQAcgBhAG4AcwBmAGUAcg'
            - 'Yml0c2FkbWluIC90cmFuc2Zlc'
            - 'AGMAaAB1AG4AawBfAHMAaQB6AGUA'
            - 'JABjAGgAdQBuAGsAXwBzAGkAegBlA'
            - 'JGNodW5rX3Npem'
            - 'QAYwBoAHUAbgBrAF8AcwBpAHoAZQ'
            - 'RjaHVua19zaXpl'
            - 'Y2h1bmtfc2l6Z'
            - 'AE8ALgBDAG8AbQBwAHIAZQBzAHMAaQBvAG4A'
            - 'kATwAuAEMAbwBtAHAAcgBlAHMAcwBpAG8Abg'
            - 'lPLkNvbXByZXNzaW9u'
            - 'SQBPAC4AQwBvAG0AcAByAGUAcwBzAGkAbwBuA'
            - 'SU8uQ29tcHJlc3Npb2'
            - 'Ty5Db21wcmVzc2lvb'
            - 'AE8ALgBNAGUAbQBvAHIAeQBTAHQAcgBlAGEAbQ'
            - 'kATwAuAE0AZQBtAG8AcgB5AFMAdAByAGUAYQBtA'
            - 'lPLk1lbW9yeVN0cmVhb'
            - 'SQBPAC4ATQBlAG0AbwByAHkAUwB0AHIAZQBhAG0A'
            - 'SU8uTWVtb3J5U3RyZWFt'
            - 'Ty5NZW1vcnlTdHJlYW'
            - '4ARwBlAHQAQwBoAHUAbgBrA'
            - '5HZXRDaHVua'
            - 'AEcAZQB0AEMAaAB1AG4Aaw'
            - 'LgBHAGUAdABDAGgAdQBuAGsA'
            - 'LkdldENodW5r'
            - 'R2V0Q2h1bm'
            - 'AEgAUgBFAEEARABfAEkATgBGAE8ANgA0A'
            - 'QASABSAEUAQQBEAF8ASQBOAEYATwA2ADQA'
            - 'RIUkVBRF9JTkZPNj'
            - 'SFJFQURfSU5GTzY0'
            - 'VABIAFIARQBBAEQAXwBJAE4ARgBPADYANA'
            - 'VEhSRUFEX0lORk82N'
            - 'AHIAZQBhAHQAZQBSAGUAbQBvAHQAZQBUAGgAcgBlAGEAZA'
            - 'cmVhdGVSZW1vdGVUaHJlYW'
            - 'MAcgBlAGEAdABlAFIAZQBtAG8AdABlAFQAaAByAGUAYQBkA'
            - 'NyZWF0ZVJlbW90ZVRocmVhZ'
            - 'Q3JlYXRlUmVtb3RlVGhyZWFk'
            - 'QwByAGUAYQB0AGUAUgBlAG0AbwB0AGUAVABoAHIAZQBhAGQA'
            - '0AZQBtAG0AbwB2AGUA'
            - '1lbW1vdm'
            - 'AGUAbQBtAG8AdgBlA'
            - 'bQBlAG0AbQBvAHYAZQ'
            - 'bWVtbW92Z'
            - 'ZW1tb3Zl'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• http://www.leeholmes.com/blog/2017/09/21/searching-for-content-in-base-64-strings/