CVE-2026-9669: Python Software Foundation Cpython

High severity, CVSS 8.2. EPSS: 0.4% chance of exploitation in the next 30 days.

bz2.BZ2Decompressor objects could be reused after a decompression error. If an application caught the resulting OSError and retried with the same decompressor, crafted input could cause the decompressor to resume from an invalid internal state and perform out-of-bounds writes to a stack buffer. This could crash the process when processing untrusted data.

Affected products

• Python Software Foundation Cpython: before 3.10.21 (fixed in 3.10.21); from 3.11.0, before 3.11.16 (fixed in 3.11.16); from 3.12.0, before 3.12.14 (fixed in 3.12.14); from 3.13.0, before 3.13.14 (fixed in 3.13.14); from 3.14.0, before 3.14.6 (fixed in 3.14.6); from 3.15.0a1, before 3.15.0b3 (fixed in 3.15.0b3)

Published 2026-06-08. Last modified 2026-08-13.