GitHub Security Advisory: GHSA-9rg3-9pvr-6p27
Package: monai (PIP)
Severity: MODERATE (CVSS 5.3)
CWE: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Vulnerable versions: <= 1.5.1
Patched in: 1.5.2

Summary: MONAI has Path Traversal (Zip Slip) in NGC Private Bundle Download

Details:
## 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()`

```python
# 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:

```python
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

```python
#!/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"}'
        )