CVE-2026-114613
MessagePack: Unbounded memory leak in msgpack C extension on strict_map_key validation failure
HIGH 7.5EPSS 0.5%
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.
- Affected
- msgpack · msgpack-python
- CVSS v3.1 GITHUB
- 7.5 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - EPSS
- 0.54% chance of exploitation in the next 30 days, 46th percentile
- Published
- 2026-10-22
- Updated
- 2026-10-23
Proof-of-concept exploits (1)
CVE references
- msgpack/msgpack-python/commit/620b0eb4c89cd72d4098564537624d9dbb2ce141REFERENCE
- msgpack/msgpack-python/releases/tag/v1.2.3REFERENCE
- msgpack/msgpack-python/security/advisories/GHSA-j586-36cw-2gc2REFERENCE