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analyzing-powershell-script-block-logging

Parse Windows PowerShell Script Block Logs (Event ID 4104) from EVTX files to detect obfuscated commands, encoded payloads, and living-off-the-land techniques. Uses python-evtx to extract and reconstruct multi-block scripts, applies entropy analysis and pattern matching for Base64-encoded commands, Invoke-Expression abuse, download cradles, and AMSI bypass attempts.

Published by mukul975 ↗mukul975/Anthropic-Cybersecurity-Skills

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analyzing-powershell-script-block-logging

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Use analyzing-powershell-script-block-logging to analyze [authorized PowerShell Operational EVTX file] for reconstructed Event ID 4104 scripts, obfuscation, encoded payloads, download cradles, and AMSI-bypass indicators; deliver a risk-scored report with MITRE ATT&CK mappings.

Required inputs

  • [authorized PowerShell Operational EVTX file]

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SKILL.md

name: analyzing-powershell-script-block-loggingdescription: Parse Windows PowerShell Script Block Logs (Event ID 4104) from EVTX  files to detect obfuscated commands, encoded payloads, and living-off-the-land techniques.  Uses python-evtx to extract and reconstruct multi-block scripts, applies entropy  analysis and pattern matching for Base64-encoded commands, Invoke-Expression abuse,  download cradles, and AMSI bypass attempts.domain: cybersecuritysubdomain: security-operationstags: - powershell- script-block-logging- event-id-4104- obfuscation-detection- windows-forensics- endpoint-securityversion: '1.0'author: mahipallicense: Apache-2.0nist_csf: - DE.CM-01- RS.MA-01- GV.OV-01- DE.AE-02mitre_attack: - T1059.001- T1027.010- T1140- T1105

Analyzing PowerShell Script Block Logging

When to Use

  • When investigating security incidents that require analyzing powershell script block logging
  • 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

  • Familiarity with security operations concepts and tools
  • Access to a test or lab environment for safe execution
  • Python 3.8+ with required dependencies installed
  • Appropriate authorization for any testing activities

Instructions

  1. Install dependencies: pip install python-evtx lxml
  2. Collect PowerShell Operational logs: Microsoft-Windows-PowerShell%4Operational.evtx
  3. Parse Event ID 4104 entries using python-evtx to extract ScriptBlockText, ScriptBlockId, and MessageNumber/MessageTotal for multi-part script reconstruction.
  4. Apply detection heuristics:
    • Base64-encoded commands (-EncodedCommand, FromBase64String)
    • Download cradles (DownloadString, DownloadFile, Invoke-WebRequest, Net.WebClient)
    • AMSI bypass patterns (AmsiUtils, amsiInitFailed)
    • Obfuscation indicators (high entropy, tick-mark insertion, string concatenation)
  5. Generate a report with reconstructed scripts, risk scores, and MITRE ATT&CK mappings.
python scripts/agent.py --evtx-file /path/to/PowerShell-Operational.evtx --output ps_analysis.json

Examples

Detect Encoded Command Execution

import base64
if "-encodedcommand" in script_text.lower():
    encoded = script_text.split()[-1]
    decoded = base64.b64decode(encoded).decode("utf-16-le")

Reconstruct Multi-Block Script

Scripts split across multiple 4104 events share a ScriptBlockId. Concatenate blocks ordered by MessageNumber to recover the full script.

analyzing-powershell-script-block-logging by mukul975 · The Skill Leaderboard