CVE-2026-9669 PUBLISHED

bz2.BZ2Decompressor reuse after error can cause a stack buffer overflow

Assigner: PSF
Reserved: 27.05.2026 Published: 08.06.2026 Updated: 08.06.2026

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.

Metrics

CVSS 4.0

CVSS Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS Score: 8.2

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	High	Integrity	None	Integrity	None
Attack Requirements	Present	Availability	High	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	Python Software Foundation
Product	CPython
Versions	Default: unaffected affected from 0 to 3.16.0 (excl.)

Credits

Bitshift (https://github.com/TheShiftedBit) reporter
Emma Smith (https://github.com/emmatyping) coordinator
Stan Ulbrych (https://github.com/StanFromIreland) remediation developer
Serhiy Storchaka (https://github.com/serhiy-storchaka) remediation reviewer

References

Problem Types

CWE-121 Stack-based buffer overflow CWE