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mukul975
44 lines
1.8 KiB
Markdown
44 lines
1.8 KiB
Markdown
---
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name: analyzing-powershell-script-block-logging
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description: >-
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Parse Windows PowerShell Script Block Logs (Event ID 4104) from EVTX files to detect obfuscated
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commands, encoded payloads, and living-off-the-land techniques. Uses python-evtx to extract and
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reconstruct multi-block scripts, applies entropy analysis and pattern matching for Base64-encoded
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commands, Invoke-Expression abuse, download cradles, and AMSI bypass attempts.
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domain: cybersecurity
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subdomain: security-operations
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tags: [analyzing, powershell, script, block]
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version: "1.0"
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author: mahipal
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license: MIT
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---
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## Instructions
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1. Install dependencies: `pip install python-evtx lxml`
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2. Collect PowerShell Operational logs: `Microsoft-Windows-PowerShell%4Operational.evtx`
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3. Parse Event ID 4104 entries using python-evtx to extract ScriptBlockText, ScriptBlockId, and MessageNumber/MessageTotal for multi-part script reconstruction.
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4. Apply detection heuristics:
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- Base64-encoded commands (`-EncodedCommand`, `FromBase64String`)
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- Download cradles (`DownloadString`, `DownloadFile`, `Invoke-WebRequest`, `Net.WebClient`)
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- AMSI bypass patterns (`AmsiUtils`, `amsiInitFailed`)
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- Obfuscation indicators (high entropy, tick-mark insertion, string concatenation)
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5. Generate a report with reconstructed scripts, risk scores, and MITRE ATT&CK mappings.
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```bash
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python scripts/agent.py --evtx-file /path/to/PowerShell-Operational.evtx --output ps_analysis.json
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```
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## Examples
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### Detect Encoded Command Execution
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```python
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import base64
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if "-encodedcommand" in script_text.lower():
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encoded = script_text.split()[-1]
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decoded = base64.b64decode(encoded).decode("utf-16-le")
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```
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### Reconstruct Multi-Block Script
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Scripts split across multiple 4104 events share a `ScriptBlockId`. Concatenate blocks ordered by `MessageNumber` to recover the full script.
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