MessagePack: Unbounded memory leak in msgpack C extension on strict_map_key validation failure

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-114613
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-22 19:17:37 UTC
Updated2026-10-22 19:17:37 UTC
DescriptionMessagePack 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-401 | CWE-401 CWE-401: Missing Release of Memory after Effective Lifetime

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Msgpack Msgpack-python affected < 1.2.3 Not specified

References

ReferenceSourceLinkTags
github.com/msgpack/msgpack-python/releases/tag/v1.2.3 [email protected] github.com
github.com/msgpack/msgpack-python/security/advisories/GHSA-j586-36cw-2gc2 [email protected] github.com
github.com/msgpack/msgpack-python/commit/620b0eb4c89cd72d4098564537624d9... [email protected] github.com
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