What’s Vulnerable › Vulnerabilities
CVE-2026-9669: bz2.BZ2Decompressor reuse after error can cause a stack buffer overflow
- Severity: high (CVSS 8.2 v4.0)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-06-08 · updated 2026-08-13
- Weakness: CWE-121
Description
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: before 3.10.21; from 3.11.0 before 3.11.16; from 3.12.0 before 3.12.14; from 3.13.0 before 3.13.14; from 3.14.0 before 3.14.6; from 3.15.0a1 before 3.15.0b3 — fixed in 3.10.21, 3.11.16, 3.12.14, 3.13.14, 3.14.6, 3.15.0b3
How to fix
Upgrade to a fixed version: Python 3.10.21, 3.11.16, 3.12.14, 3.13.14. Check the vendor advisory for mitigations.
References
- https://github.com/python/cpython/commit/157a5df8cb5d82b33f918a7489e72ce95ceb12b6
- https://github.com/python/cpython/commit/1ba6135eae75ad8413413caeeedb56ae72320636
- https://github.com/python/cpython/commit/5755d0f083949ff3c5bf3a37e673e24e306b036e
- https://github.com/python/cpython/commit/619a12b2e545391dc436b3af79dda22337382a6f
- https://github.com/python/cpython/commit/938ec030e90c5e53f1faac6fab1643f14e4f4a79
- https://github.com/python/cpython/commit/991e6cf86496718c4ef00b362d640e00cb5c85b2
- https://github.com/python/cpython/commit/d3ca26983dfbccdf609f24ff5877dc3118e4702d
- https://github.com/python/cpython/issues/150599
- https://github.com/python/cpython/pull/150600
- https://mail.python.org/archives/list/security-announce@python.org/thread/DBJZETMGUIFK7DVUWMOXHD3Z6IX2QPSX/
- http://www.openwall.com/lists/oss-security/2026/06/08/17
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