huntrule

Windows PowerShell: Detect Command Lines with Suspicious UTF-16 Base64 Obfuscation Patterns

Alerts on PowerShell command lines containing suspicious UTF-16/Base64 obfuscation fragments indicative of hidden script logic.

FreeUnreviewedSigmahighv1
title: "Windows PowerShell: Detect Command Lines with Suspicious UTF-16 Base64 Obfuscation Patterns"
id: 6238a787-13d7-4c31-99fc-cf52551c2dd6
status: test
description: This rule flags Windows process creation events where the PowerShell command line contains specific UTF-16/Base64-encoded string fragments and related obfuscation markers. Such encoded payloads are commonly used by attackers to hide malicious logic and reduce detection by signature-based tooling. It relies on process creation telemetry, specifically the CommandLine field, to match the presence of those encoded substrings.
references:
  - https://app.any.run/tasks/fcadca91-3580-4ede-aff4-4d2bf809bf99/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_powershell_base64_encoded_obfusc.yml
author: Florian Roth (Nextron Systems), Huntrule Team
date: 2022-07-11
modified: 2023-02-14
tags:
  - attack.stealth
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    CommandLine|contains:
      - IAAtAGIAeABvAHIAIAAwAHgA
      - AALQBiAHgAbwByACAAMAB4A
      - gAC0AYgB4AG8AcgAgADAAeA
      - AC4ASQBuAHYAbwBrAGUAKAApACAAfAAg
      - AuAEkAbgB2AG8AawBlACgAKQAgAHwAI
      - ALgBJAG4AdgBvAGsAZQAoACkAIAB8AC
      - AHsAMQB9AHsAMAB9ACIAIAAtAGYAI
      - B7ADEAfQB7ADAAfQAiACAALQBmAC
      - AewAxAH0AewAwAH0AIgAgAC0AZgAg
      - AHsAMAB9AHsAMwB9ACIAIAAtAGYAI
      - B7ADAAfQB7ADMAfQAiACAALQBmAC
      - AewAwAH0AewAzAH0AIgAgAC0AZgAg
      - AHsAMgB9AHsAMAB9ACIAIAAtAGYAI
      - B7ADIAfQB7ADAAfQAiACAALQBmAC
      - AewAyAH0AewAwAH0AIgAgAC0AZgAg
      - AHsAMQB9AHsAMAB9ACcAIAAtAGYAI
      - B7ADEAfQB7ADAAfQAnACAALQBmAC
      - AewAxAH0AewAwAH0AJwAgAC0AZgAg
      - AHsAMAB9AHsAMwB9ACcAIAAtAGYAI
      - B7ADAAfQB7ADMAfQAnACAALQBmAC
      - AewAwAH0AewAzAH0AJwAgAC0AZgAg
      - AHsAMgB9AHsAMAB9ACcAIAAtAGYAI
      - B7ADIAfQB7ADAAfQAnACAALQBmAC
      - AewAyAH0AewAwAH0AJwAgAC0AZgAg
  condition: selection
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: 8d01b53f-456f-48ee-90f6-bc28e67d4e35
    type: derived

What it detects

This rule flags Windows process creation events where the PowerShell command line contains specific UTF-16/Base64-encoded string fragments and related obfuscation markers. Such encoded payloads are commonly used by attackers to hide malicious logic and reduce detection by signature-based tooling. It relies on process creation telemetry, specifically the CommandLine field, to match the presence of those encoded substrings.

Known false positives

  • Unknown

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.