CVE-2026-9669: CWE-121 Stack-based buffer overflow in Python Software Foundation CPython
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.
AI Analysis
Technical Summary
The bz2.BZ2Decompressor object in CPython can be reused after an OSError caused by a decompression error. If an application catches this error and retries decompression using the same decompressor instance, crafted input may cause the decompressor to resume from an invalid internal state. This leads to out-of-bounds writes on the stack, resulting in a stack-based buffer overflow vulnerability (CWE-121). The flaw affects CPython versions 3.14.0 and 3.15.0a1. The CVSS 4.0 base score is 8.2, indicating high severity. No official patch or remediation level is currently documented.
Potential Impact
Successful exploitation can cause the Python process to crash due to out-of-bounds writes on the stack when processing crafted untrusted data. This may lead to denial of service. There is no indication of code execution or privilege escalation from the provided data.
Mitigation Recommendations
Patch status is not yet confirmed — check the Python Software Foundation advisory for current remediation guidance. Until a fix is available, avoid reusing bz2.BZ2Decompressor objects after a decompression error in untrusted contexts.
CVE-2026-9669: CWE-121 Stack-based buffer overflow in Python Software Foundation CPython
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.
CVSS v4.0
Score 8.2high
Affected software
Python Software Foundation
CPython
pkg:github/CPythonRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The bz2.BZ2Decompressor object in CPython can be reused after an OSError caused by a decompression error. If an application catches this error and retries decompression using the same decompressor instance, crafted input may cause the decompressor to resume from an invalid internal state. This leads to out-of-bounds writes on the stack, resulting in a stack-based buffer overflow vulnerability (CWE-121). The flaw affects CPython versions 3.14.0 and 3.15.0a1. The CVSS 4.0 base score is 8.2, indicating high severity. No official patch or remediation level is currently documented.
Potential Impact
Successful exploitation can cause the Python process to crash due to out-of-bounds writes on the stack when processing crafted untrusted data. This may lead to denial of service. There is no indication of code execution or privilege escalation from the provided data.
Mitigation Recommendations
Patch status is not yet confirmed — check the Python Software Foundation advisory for current remediation guidance. Until a fix is available, avoid reusing bz2.BZ2Decompressor objects after a decompression error in untrusted contexts.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- PSF
- Date Reserved
- 2026-05-27T03:13:18.152Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6a2746c4e29bf47b50b779cf
Added to database: 06/08/2026, 22:48:36 UTC
Last enriched: 08/12/2026, 13:41:40 UTC
Last updated: 09/11/2026, 22:06:35 UTC
Views: 239
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