Anthropic-Cybersecurity-Skills/skills/hunting-for-anomalous-powershell-execution/SKILL.md

name, description, domain, subdomain, tags, version, author, license, nist_csf

name	description	domain	subdomain	tags	version	author	license	nist_csf
hunting-for-anomalous-powershell-execution	Hunt for malicious PowerShell activity by analyzing Script Block Logging (Event 4104), Module Logging (Event 4103), and process creation events. The analyst parses Windows Event Log EVTX files to detect obfuscated commands, AMSI bypass attempts, encoded payloads, credential dumping keywords, and suspicious download cradles. Activates for requests involving PowerShell threat hunting, script block analysis, encoded command detection, or AMSI bypass identification.	cybersecurity	threat-hunting	powershell script-block-logging event-4104 amsi threat-hunting evtx obfuscation	1.0	mahipal	Apache-2.0	DE.CM-01 DE.AE-02 DE.AE-07 ID.RA-05

Hunting for Anomalous PowerShell Execution

Overview

PowerShell Script Block Logging (Event ID 4104) records the full deobfuscated script text executed on a Windows endpoint, making it the primary data source for hunting malicious PowerShell. Combined with Module Logging (4103) and process creation events, analysts can detect encoded commands, AMSI bypass patterns, download cradles, credential theft tools, and fileless attack techniques even when the attacker uses obfuscation layers.

When to Use

• When investigating security incidents that require hunting for anomalous powershell execution
• When building detection rules or threat hunting queries for this domain
• When SOC analysts need structured procedures for this analysis type
• When validating security monitoring coverage for related attack techniques

Prerequisites

• Windows Event Log exports (.evtx) from Microsoft-Windows-PowerShell/Operational
• Python 3.8+ with python-evtx and lxml libraries
• Script Block Logging enabled via Group Policy
• Understanding of common PowerShell attack techniques

Steps

1. Parse EVTX files extracting Event 4104 script block text and metadata
2. Reassemble multi-part script blocks using ScriptBlock ID correlation
3. Scan script text for AMSI bypass indicators and obfuscation patterns
4. Detect encoded command execution and base64 payloads
5. Identify download cradles, credential dumping, and lateral movement commands
6. Score and prioritize findings by threat severity

Expected Output

{
  "total_events": 1247,
  "suspicious_events": 23,
  "amsi_bypass_attempts": 2,
  "encoded_commands": 8,
  "download_cradles": 5,
  "credential_access": 3
}