---
id: CVE-2026-114613
title: >-
  MessagePack: Unbounded memory leak in msgpack C extension on strict_map_key
  validation failure
summary: >-
  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). …
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
cwe:
  - CWE-401
vendor: msgpack
product: msgpack-python
affected:
  - msgpack-python < 1.2.3
published: '2026-10-22'
updated: '2026-10-22'
sourceUpdated: '2026-10-22T18:22:40.544Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-114613'
references:
  - url: >-
      https://github.com/msgpack/msgpack-python/security/advisories/GHSA-j586-36cw-2gc2
    label: >-
      https://github.com/msgpack/msgpack-python/security/advisories/GHSA-j586-36cw-2gc2
  - url: >-
      https://github.com/msgpack/msgpack-python/commit/620b0eb4c89cd72d4098564537624d9dbb2ce141
    label: >-
      https://github.com/msgpack/msgpack-python/commit/620b0eb4c89cd72d4098564537624d9dbb2ce141
  - url: 'https://github.com/msgpack/msgpack-python/releases/tag/v1.2.3'
    label: 'https://github.com/msgpack/msgpack-python/releases/tag/v1.2.3'
tags:
  - cve.org
ingestedAt: '2026-10-22T22:00:50.363Z'
---

## Overview

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-python < 1.2.3`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.