Powershell Base64 Encoded MpPreference Cmdlet — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: high. Source dates: 2022-03-04 / 2023-01-30.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: e7ce2f3545919f5f03bd0e0481e578b5b1f61a19a98cf08ce6333d4357bd9e3a

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 MpPreference Cmdlet
id: c6fb44c6-71f5-49e6-9462-1425d328aee3
status: test
description: Detects base64 encoded "MpPreference" PowerShell cmdlet code that tries to modifies or tamper with Windows Defender AV
references:
    - https://learn.microsoft.com/en-us/defender-endpoint/configure-process-opened-file-exclusions-microsoft-defender-antivirus
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1562.001/T1562.001.md
    - https://twitter.com/AdamTheAnalyst/status/1483497517119590403
author: Florian Roth (Nextron Systems)
date: 2022-03-04
modified: 2023-01-30
tags:
    - attack.defense-impairment
    - attack.t1685
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - CommandLine|base64offset|contains:
              - 'Add-MpPreference '
              - 'Set-MpPreference '
              - 'add-mppreference '
              - 'set-mppreference '
        - CommandLine|contains:
              # UTF16-LE
              - 'QQBkAGQALQBNAHAAUAByAGUAZgBlAHIAZQBuAGMAZQAgA'
              - 'EAZABkAC0ATQBwAFAAcgBlAGYAZQByAGUAbgBjAGUAIA'
              - 'BAGQAZAAtAE0AcABQAHIAZQBmAGUAcgBlAG4AYwBlACAA'
              - 'UwBlAHQALQBNAHAAUAByAGUAZgBlAHIAZQBuAGMAZQAgA'
              - 'MAZQB0AC0ATQBwAFAAcgBlAGYAZQByAGUAbgBjAGUAIA'
              - 'TAGUAdAAtAE0AcABQAHIAZQBmAGUAcgBlAG4AYwBlACAA'
              - 'YQBkAGQALQBtAHAAcAByAGUAZgBlAHIAZQBuAGMAZQAgA'
              - 'EAZABkAC0AbQBwAHAAcgBlAGYAZQByAGUAbgBjAGUAIA'
              - 'hAGQAZAAtAG0AcABwAHIAZQBmAGUAcgBlAG4AYwBlACAA'
              - 'cwBlAHQALQBtAHAAcAByAGUAZgBlAHIAZQBuAGMAZQAgA'
              - 'MAZQB0AC0AbQBwAHAAcgBlAGYAZQByAGUAbgBjAGUAIA'
              - 'zAGUAdAAtAG0AcABwAHIAZQBmAGUAcgBlAG4AYwBlACAA'
    condition: selection
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://learn.microsoft.com/en-us/defender-endpoint/configure-process-opened-file-exclusions-microsoft-defender-antivirus
• https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1562.001/T1562.001.md
• https://twitter.com/AdamTheAnalyst/status/1483497517119590403