Application crash via unreset Unpacker parser context
Published Jun 30, 2026 · Updated Jun 30, 2026
Use-after-free in MessagePack for Python before 1.2.1 allows remote attackers to crash applications that reuse an Unpacker. On a failed unpack or skip, the C extension returns without clearing and reinitializing the Unpacker's parser context, so later reuse accesses stale object references. Exploitation requires attacker-controlled MessagePack data, a caught exception, and reuse of the same Unpacker; the hosting process can terminate with SIGSEGV.
Summary
What happened
Use-after-free in MessagePack for Python before 1.2.1 allows remote attackers to crash applications that reuse an Unpacker. On a failed unpack or skip, the C extension returns without clearing and reinitializing the Unpacker's parser context, so later reuse accesses stale object references. Exploitation requires attacker-controlled MessagePack data, a caught exception, and reuse of the same Unpacker; the hosting process can terminate with SIGSEGV.
The record
- CVE
- CVE-2026-57585
- Published
- Jun 30, 2026
- Updated
- Jun 30, 2026
- Vendor
- MessagePack-CSharp
- Product
- MessagePack for Python
- Classifications
- CWE-416, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 30, 2026CVE publishedPublication date reported by the CVE source.
- Jun 30, 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=< 1.2.1
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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