CVE-2026-114613
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.
How to fix
- msgpack1.2.3 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| msgpackPyPI | v < 1.2.3 | 1.2.3 |
| microsoft azl3_python-msgpack_1.0.5-3 | No range specified | — |
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