Detectionhightest

Powershell Base64 Encoded MpPreference Cmdlet

Detects base64 encoded "MpPreference" PowerShell cmdlet code that tries to modifies or tamper with Windows Defender AV

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Launch

Florian Roth (Nextron Systems)Created Fri Mar 04Updated Mon Jan 30c6fb44c6-71f5-49e6-9462-1425d328aee3windows

Log Source

WindowsProcess Creation

ProductWindows← raw: windows

CategoryProcess Creation← raw: process_creation

Events generated when a new process is spawned on the system. Covers command-line arguments, parent/child relationships, and process metadata.

Detection Logic

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