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SKILL verified Apache-2.0 Self-run

Analyzing Compiled Python Malware

skill-meltedinhex-analyst-ai-pack-analyzing-compiled-python-malware · by meltedinhex

Analyzes Python-based malware packaged as PyInstaller/py2exe executables by detecting

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Install

$ agentstack add skill-meltedinhex-analyst-ai-pack-analyzing-compiled-python-malware

✓ scanned · ✓ verified — works with Claude Code, Cursor, and more.

Security review

✓ Passed

No issues found. Passed automated security review. · v0.1.0 How review works →

  • ✓ Prompt-injection patterns
  • ✓ Secret / credential exfiltration
  • ✓ Dangerous shell & filesystem operations
  • ✓ Untrusted network calls
  • ✓ Known-malicious package signatures

What it can access

  • ✓ Network access No
  • ✓ Filesystem access No
  • ✓ Shell / process execution No
  • ✓ Environment & secrets No
  • ✓ Dynamic code execution No

From automated source analysis of v0.1.0. “Used” means the capability is present in the source — more access means more to trust, not that it’s unsafe.

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About

Analyzing Compiled Python Malware

When to Use

  • You have an executable that is actually a frozen Python app (PyInstaller, py2exe, cx_Freeze) and

need to identify the packer and locate the embedded Python modules.

  • You want to extract .pyc files for decompilation.

Do not use this to run the executable — it identifies and locates the embedded archive statically. Decompile extracted .pyc in an isolated environment.

Prerequisites

  • The frozen executable (read inertly).

Safety & Handling

  • Read bytes statically; treat extracted modules as malicious until reviewed.

Workflow

Step 1: Detect the packer

python scripts/analyst.py detect sample.exe

Looks for PyInstaller markers (pyi-, PYZ-00.pyz, the MEI CArchive cookie MEI\014\013\012\013\016), py2exe (PYTHONSCRIPT, zipfile.zip), and embedded python3x.dll references.

Step 2: Locate the embedded archive

Find the CArchive cookie near the end of the file and report the offset and the embedded Python version string (python3.x).

Step 3: Extract and decompile

Use a PyInstaller extractor to dump the archive, then decompile .pyc (matching the detected Python version) for source recovery.

Step 4: Analyze the source

Review the recovered Python for C2, persistence, and capability; map to ATT&CK.

Validation

  • The packer is identified by its specific marker, not just the presence of Python strings.
  • The CArchive cookie offset and Python version are reported when PyInstaller is present.
  • Findings distinguish the bootloader stub from the embedded Python payload.

Pitfalls

  • .pyc version mismatch breaking decompilation — match the interpreter version.
  • Stripped/obfuscated bytecode (e.g., custom magic) needing header repair before decompiling.
  • Encrypted PYZ archives (PyInstaller --key) requiring the key.

References

  • See [references/api-reference.md](references/api-reference.md) for the detector.
  • PyInstaller archive and Python bytecode references (linked in frontmatter).

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

Install and usage instructions live in the source repository linked above.

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Versions

  • v0.1.0 Imported from the upstream source.

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