# 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.

- Skill: `thedixitjain/analyzing-powershell-script-block-logging` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds add thedixitjain/analyzing-powershell-script-block-logging`
- Raw SKILL.md: https://api.skillmd.com/api/skills/thedixitjain/analyzing-powershell-script-block-logging/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: thedixitjain (https://skillmd.com/u/thedixitjain)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/thedixitjain/analyzing-powershell-script-block-logging

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# 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.

```bash
python scripts/agent.py --evtx-file /path/to/PowerShell-Operational.evtx --output ps_analysis.json
```

## Examples

### Detect Encoded Command Execution
```python
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.

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**Source:** [`mukul975/Anthropic-Cybersecurity-Skills`](https://github.com/mukul975/Anthropic-Cybersecurity-Skills) → `skills/analyzing-powershell-script-block-logging/SKILL.md`