Vulnerability · Published Oct 22, 2026 · Assigned by GitHub_M

CVE-2026-114613MessagePack: Unbounded memory leak in msgpack C extension on strict_map_key validation failure

High 7.5

In plain English

A high-severity memory leak in msgpack-python from msgpack. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 46% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.5%top 54.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	python-msgpack	no fix listed	DEBIAN-CVE-2026-114613
Debian:13	python-msgpack	no fix listed	DEBIAN-CVE-2026-114613
Debian:14	python-msgpack	no fix listed	DEBIAN-CVE-2026-114613
PyPI	msgpack	1.2.3	GHSA-j586-36cw-2gc2

Affected products (as reported)

Vendor	Product	Versions
msgpack	msgpack-python	< 1.2.3

Weakness: CWE-401 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/msgpack/msgpack-python/security/advisories/GHSA-j586-36cw-2gc2 x_refsource_CONFIRM
https://github.com/msgpack/msgpack-python/commit/620b0eb4c89cd72d4098564537624d9dbb2ce141 x_refsource_MISC
https://github.com/msgpack/msgpack-python/releases/tag/v1.2.3 x_refsource_MISC