PowerShell Base64 Encoded Reflective Assembly Load

Severity: high
Author: Christian Burkard (Nextron Systems), pH-T (Nextron Systems)
Source: upstream

Detects base64 encoded .NET reflective loading of Assembly

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell
Defense Evasion	`T1027` Obfuscated Files or Information, `T1620` Reflective Code Loading

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: 'AFsAcgBlAGYAbABlAGMAdABpAG8AbgAuAGEAcwBzAGUAbQBiAGwAeQBdADoAOgAoACIATABvAGEAZAAiAC'
CommandLine|contains: 'AWwByAGUAZgBsAGUAYwB0AGkAbwBuAC4AYQBzAHMAZQBtAGIAbAB5AF0AOgA6ACgAIgBMAG8AYQBkACIAK'
CommandLine|contains: 'BbAHIAZQBmAGwAZQBjAHQAaQBvAG4ALgBhAHMAcwBlAG0AYgBsAHkAXQA6ADoAKAAiAEwAbwBhAGQAIgAp'
CommandLine|contains: 'WwBSAGUAZgBsAGUAYwB0AGkAbwBuAC4AQQBzAHMAZQBtAGIAbAB5AF0AOgA6ACgAIgBMAG8AYQBkACIAKQ'
CommandLine|contains: 'WwBSAGUAZgBsAGUAYwB0AGkAbwBuAC4AQQBzAHMAZQBtAGIAbAB5AF0AOgA6AEwAbwBhAGQAKA'
CommandLine|contains: 'WwByAGUAZgBsAGUAYwB0AGkAbwBuAC4AYQBzAHMAZQBtAGIAbAB5AF0AOgA6AEwAbwBhAGQAKA'
CommandLine|contains: 'bAFIAZQBmAGwAZQBjAHQAaQBvAG4ALgBBAHMAcwBlAG0AYgBsAHkAXQA6ADoAKAAiAEwAbwBhAGQAIgApA'
CommandLine|contains: 'bAFIAZQBmAGwAZQBjAHQAaQBvAG4ALgBBAHMAcwBlAG0AYgBsAHkAXQA6ADoATABvAGEAZAAoA'
CommandLine|contains: 'bAHIAZQBmAGwAZQBjAHQAaQBvAG4ALgBhAHMAcwBlAG0AYgBsAHkAXQA6ADoATABvAGEAZAAoA'
CommandLine|contains: 'sAUgBlAGYAbABlAGMAdABpAG8AbgAuAEEAcwBzAGUAbQBiAGwAeQBdADoAOgAoACIATABvAGEAZAAiACkA'
CommandLine|contains: 'sAUgBlAGYAbABlAGMAdABpAG8AbgAuAEEAcwBzAGUAbQBiAGwAeQBdADoAOgBMAG8AYQBkACgA'
CommandLine|contains: 'sAcgBlAGYAbABlAGMAdABpAG8AbgAuAGEAcwBzAGUAbQBiAGwAeQBdADoAOgBMAG8AYQBkACgA'

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.