high7.5
CVE-2026-114613
MessagePack: Unbounded memory leak in msgpack C extension on strict_map_key validation failure
Impact
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 packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | msgpack | < 1.2.3 | 1.2.3 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-j586-36cw-2gc2
- https://github.com/msgpack/msgpack-python/security/advisories/GHSA-j586-36cw-2gc2
- https://nvd.nist.gov/vuln/detail/CVE-2026-114613
- https://github.com/msgpack/msgpack-python/commit/620b0eb4c89cd72d4098564537624d9dbb2ce141
- https://github.com/msgpack/msgpack-python/releases/tag/v1.2.3