BIT-libpython-2026-15310: zipfile: bzip2/LZMA/Zstandard members decompress without a max_length bound, defeating chunked-read memory limits

Published Aug 25, 2026

Updated

When decompressing crafted zip files using the bzip/LZMA/Zstandard

compressions, Python could use an attacker-controlled size to

pre-allocate memory, possibly resulting in memory exhaustion.

Affected Software

1 affected component

Python Software Foundation Python

Event History

Aug 25, 2026

CVE Published

via OSV·03:07 PM

Data Sourced

via OSV·03:07 PM

DescriptionSeverityWeakness

Frequently Asked Questions

Who is exposed to this issue?

Applications that decompress attacker-controlled ZIP files using Python’s zipfile support for bzip2, LZMA, or Zstandard members are exposed. The impact described is memory exhaustion from attacker-controlled decompressed size information.

What must an attacker do to trigger the issue?

An attacker needs to provide a crafted ZIP file and have it decompressed by the affected application. User interaction is required according to the supplied vector, and no privileges are required.

Does limiting ZIP reads to chunks prevent the memory issue?

No. The issue occurs because these compression methods can decompress without a max_length bound, defeating chunked-read memory limits and allowing attacker-controlled pre-allocation.

BIT-libpython-2026-15310: zipfile: bzip2/LZMA/Zstandard members decompress without a max_length bound, defeating chunked-read memory limits

Affected Software

Event History

Frequently Asked Questions

Who is exposed to this issue?

What must an attacker do to trigger the issue?

Does limiting ZIP reads to chunks prevent the memory issue?

Company

Resources

Contact

Frequently Asked Questions

Who is exposed to this issue?

What must an attacker do to trigger the issue?

Does limiting ZIP reads to chunks prevent the memory issue?