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

影響: pip:msgpack < 1.2.3 → 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. The report measured approximately 4 MiB retained pe…

Read on GitHub Advisory Database

On 10/28/2026, 12:04 AM, GitHub Advisory Database published "MessagePack: Unbounded memory leak in msgpack C extension on strict_map_key validation failure" (type: Advisory). Severity is "High" (high). Related technologies: Python. CVE: CVE-2026-114613.