CVE-2026-114613

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

Published Oct 22, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-j586-36cw-2gc2 MessagePack: Unbounded memory leak in msgpack C extension on strict_map_key validation failure
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

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

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Oct 23, 2026, 9:08 PM
Reserved
Oct 21, 2026, 8:34 PM
Status
Awaiting Analysis
Published
Oct 22, 2026, 7:17 PM
Modified
Oct 23, 2026, 9:17 PM
Severity
Important
Public date
Oct 22, 2026, 6:22 PM