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.
Published: 2026-10-22
Score: 7.5 High
EPSS: n/a
KEV: No
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History

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'}


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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

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cve-icon OpenCVE Enrichment

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Weaknesses