MessagePack is the serializer implementation for Python msgpack.org. Prior to 1.2.3, the msgpack-python C extension (msgpack._cmsgpack) leaks a decoded map value when deserialization rejects a key with strict_map_key=True (the default). Repeated malformed inputs can cause unbounded process memory growth and denial of service in applications that deserialize attacker-controlled MessagePack data. Both unpackb() and the streaming Unpacker API are affected. The pure-Python fallback does not exhibit this leak in the reported tests. This issue is fixed in version 1.2.3.
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Fixes

Solution

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Workaround

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History

Fri, 23 Oct 2026 12:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-772
References
Metrics threat_severity

None

threat_severity

Important


Fri, 23 Oct 2026 04:45:00 +0000

Type Values Removed Values Added
First Time appeared Msgpack
Msgpack msgpack-python
Vendors & Products Msgpack
Msgpack msgpack-python

Fri, 23 Oct 2026 00:45:00 +0000

Type Values Removed Values Added
Description MessagePack is the serializer implementation for Python msgpack.org. Prior to 1.2.3, the msgpack-python C extension (msgpack._cmsgpack) leaks a decoded map value when deserialization rejects a key with strict_map_key=True (the default). Repeated malformed inputs can cause unbounded process memory growth and denial of service in applications that deserialize attacker-controlled MessagePack data. Both unpackb() and the streaming Unpacker API are affected. The pure-Python fallback does not exhibit this leak in the reported tests. This issue is fixed in version 1.2.3.
Title MessagePack: Unbounded memory leak in msgpack C extension on strict_map_key validation failure
Weaknesses CWE-401
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-10-22T18:22:40.544Z

Reserved: 2026-10-21T20:34:25.599Z

Link: CVE-2026-114613

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-22T19:17:37.733

Modified: 2026-10-22T19:17:37.733

Link: CVE-2026-114613

cve-icon Redhat

Severity : Important

Publid Date: 2026-10-22T18:22:40Z

Links: CVE-2026-114613 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-23T13:30:07Z

Weaknesses