What it does. 'Hunt for malicious PowerShell activity by analyzing Script Block Logging Part of mukul975/Anthropic-Cybersecurity-Skills (817 security skills) (mukul975/Anthropic-Cybersecurity-Skills).

Install

• npx skills add mukul975/Anthropic-Cybersecurity-Skills --skill hunting-for-anomalous-powershell-execution, or copy the skill folder into ~/.claude/skills/hunting-for-anomalous-powershell-execution/.
• Raw file: curl -sL https://raw.githubusercontent.com/mukul975/Anthropic-Cybersecurity-Skills/HEAD/skills/hunting-for-anomalous-powershell-execution/SKILL.md

SKILL.md (verbatim)

name: hunting-for-anomalous-powershell-execution
description: '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.

  '
domain: cybersecurity
subdomain: threat-hunting
tags:
- powershell
- script-block-logging
- event-4104
- amsi
- threat-hunting
- evtx
- obfuscation
version: '1.0'
author: mahipal
license: Apache-2.0
nist_csf:
- DE.CM-01
- DE.AE-02
- DE.AE-07
- ID.RA-05
mitre_attack:
- T1046
- T1057
- T1082
- T1083
- T1003

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
}

Other files in this skill

• LICENSE
• references/api-reference.md
• scripts/agent.py

references/api-reference.md (verbatim)

Hunting for Anomalous PowerShell Execution — API Reference

Windows Event Log IDs

Event 4104 XML Fields

AMSI Bypass Indicators

Suspicious PowerShell Keywords

Download Cradle Patterns

Obfuscation Indicators

python-evtx Library Usage

import Evtx.Evtx as evtx
from lxml import etree

with evtx.Evtx("PowerShell-Operational.evtx") as log:
    for record in log.records():
        xml = record.xml()
        root = etree.fromstring(xml.encode("utf-8"))
        # Extract EventID, EventData fields

CLI Usage

# Hunt for suspicious PowerShell in EVTX file
python agent.py --evtx /path/to/PowerShell-Operational.evtx

# Limit events parsed
python agent.py --evtx logs.evtx --max-events 5000

# Save report to JSON
python agent.py --evtx logs.evtx --output hunt_report.json

Group Policy Settings for Script Block Logging

Computer Configuration > Administrative Templates > Windows Components
  > Windows PowerShell > Turn on PowerShell Script Block Logging
    -> Enabled
    -> Log script block invocation start / stop events: Checked

External References

• Splunk: Hunting for Malicious PowerShell using Script Block Logging
• block-parser: PowerShell Script Block Log Parser
• Windows Forensic Artifacts: EVTX 4104
• Elastic: AMSI Bypass via PowerShell Detection Rule

Back to mukul975/Anthropic-Cybersecurity-Skills (817 security skills) or Agent skills.