MobSF Vulnerable to Zip Bomb Denial of Service via Per-File Size Limit Bypass in ZIP/APK Extraction

Summary

When extracting uploaded ZIP/APK files, MobSF checks if individual files exceed ZIP_MAX_UNCOMPRESSED_FILE_SIZE (400 MB) and logs "Skipping" — but the code lacks a continue statement, so extraction proceeds anyway. The log message is misleading; the file is still written to disk.

Verified Impact (Code Audit)

The vulnerable code path in shared_func.py lines 153–182:

# Line 156: Size check
if fileinfo.file_size > settings.ZIP_MAX_UNCOMPRESSED_FILE_SIZE:
    size_mb = fileinfo.file_size / (1024 * 1024)
    msg = (f'File too large ({size_mb:.2f} MB). Skipping '
           f'{sanitize_for_logging(file_path)}')
    logger.warning(msg)
    # ← BUG: No 'continue' here! Execution falls through.

# Line 161: Total size check (separate)
if total_size > settings.ZIP_MAX_UNCOMPRESSED_TOTAL_SIZE:
    raise Exception(msg)

# Line 171-178: Permission fixing (only dirs get 'continue')
if fileinfo.is_dir():
    continue
else:
    fileinfo.external_attr = ...

# Line 182: EXTRACTION ALWAYS HAPPENS FOR FILES
try:
    zipptr.extract(file_path, ext_path)   # ← Runs regardless of size check