Powershell Base64 Encoded MpPreference Cmdlet

Severity: high
Author: Florian Roth (Nextron Systems)
Source: upstream

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

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1562.001` Impair Defenses: Disable or Modify Tools

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `selection`

or:
CommandLine|contains: 'Add-MpPreference '
CommandLine|contains: 'BAGQAZAAtAE0AcABQAHIAZQBmAGUAcgBlAG4AYwBlACAA'
CommandLine|contains: 'EAZABkAC0ATQBwAFAAcgBlAGYAZQByAGUAbgBjAGUAIA'
CommandLine|contains: 'EAZABkAC0AbQBwAHAAcgBlAGYAZQByAGUAbgBjAGUAIA'
CommandLine|contains: 'MAZQB0AC0ATQBwAFAAcgBlAGYAZQByAGUAbgBjAGUAIA'
CommandLine|contains: 'MAZQB0AC0AbQBwAHAAcgBlAGYAZQByAGUAbgBjAGUAIA'
CommandLine|contains: 'QQBkAGQALQBNAHAAUAByAGUAZgBlAHIAZQBuAGMAZQAgA'
CommandLine|contains: 'Set-MpPreference '
CommandLine|contains: 'TAGUAdAAtAE0AcABQAHIAZQBmAGUAcgBlAG4AYwBlACAA'
CommandLine|contains: 'UwBlAHQALQBNAHAAUAByAGUAZgBlAHIAZQBuAGMAZQAgA'
CommandLine|contains: 'YQBkAGQALQBtAHAAcAByAGUAZgBlAHIAZQBuAGMAZQAgA'
CommandLine|contains: 'add-mppreference '
CommandLine|contains: 'cwBlAHQALQBtAHAAcAByAGUAZgBlAHIAZQBuAGMAZQAgA'
CommandLine|contains: 'hAGQAZAAtAG0AcABwAHIAZQBmAGUAcgBlAG4AYwBlACAA'
CommandLine|contains: 'set-mppreference '
CommandLine|contains: 'zAGUAdAAtAG0AcABwAHIAZQBmAGUAcgBlAG4AYwBlACAA'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.