Rodion111/joblib-bz2-decompression-bomb-poc

Joblib BZ2 Decompression Bomb PoC

Vulnerability: BZ2CompressorWrapper.decompressor_file() has no decompression size limit File: joblib/compressor.py line ~145 Severity: CVSS 7.5 High (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) CWE: CWE-409 (Improper Handling of Highly Compressed Data) Affected: joblib <= 1.5.x (all versions with BZ2 support) Reported via: huntr.com bug bounty

PoC Files

File	Compressed Size	Decompressed	Ratio
joblib_bz2_100mb_bomb.joblib.bz2	347 bytes	100 MB	288,184:1
joblib_bz2_1gb_bomb.joblib.bz2	957 bytes	1 GB	1,044,932:1

Reproduction

import joblib

# 957 bytes → 1 GB memory allocation → OOM crash
data = joblib.load("joblib_bz2_1gb_bomb.joblib.bz2")
# Process is killed by OOM on systems with < 1 GB available memory

Root Cause

# joblib/compressor.py, BZ2CompressorWrapper.decompressor_file()
def decompressor_file(self, fileobj):
    fileobj = self.fileobj_factory(fileobj, "rb")  # bz2.BZ2File(fileobj, "rb")
    return fileobj  # No maxsize limit — reads until EOF

Compare to the LZMA bomb filed earlier (also lacks maxsize) — BZ2 is even more efficient:

• LZMA bomb: 15,000 bytes → 100 MB
• BZ2 bomb: 347 bytes → 100 MB (this report)
• BZ2 bomb: 957 bytes → 1 GB (this report)

Responsible Disclosure

Filed via huntr.com Model File Format bug bounty program.