Process crash via decompressor error-state reuse
Published Jun 8, 2026 · Updated Jun 8, 2026
Stack-based buffer overflow in CPython's bz2 module allows remote attackers to crash a process by supplying crafted bzip2 data. After bz2.BZ2Decompressor raises OSError for malformed input, the reusable object resumes libbz2 from an invalid internal state and performs out-of-bounds writes to a stack buffer. Exploitation requires an application to catch that error and retry untrusted data with the same decompressor; the documented consequence is a process crash.
Summary
What happened
Stack-based buffer overflow in CPython's bz2 module allows remote attackers to crash a process by supplying crafted bzip2 data. After bz2.BZ2Decompressor raises OSError for malformed input, the reusable object resumes libbz2 from an invalid internal state and performs out-of-bounds writes to a stack buffer. Exploitation requires an application to catch that error and retry untrusted data with the same decompressor; the documented consequence is a process crash.
The record
- CVE
- CVE-2026-9669
- Published
- Jun 8, 2026
- Updated
- Jun 8, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-121, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 8, 2026CVE publishedPublication date reported by the CVE source.
- Jun 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <3.16.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
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Technologies
Your stack
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Your stack
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