---
id: CVE-2026-107301
title: msgpack5 is a msgpack v5 implementation for node.js and the browser
summary: >-
  msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to
  6.1.0, constructing msgpack5 with an empty or partial options object disables
  the default protoAction: 'error' protection. A decoded map containing a
  __proto__…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L'
cwe:
  - CWE-1321
vendor: msgpack5
product: msgpack5
affected:
  - msgpack5 < 6.1.0
patched:
  - msgpack5 6.1.0
published: '2026-10-08'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T20:48:36.970'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-107301'
references:
  - url: >-
      https://github.com/mcollina/msgpack5/commit/20e82600ac9462e679c8a45e5723315f21e2c774
    label: security-advisories@github.com
  - url: 'https://github.com/mcollina/msgpack5/releases/tag/v6.1.0'
    label: security-advisories@github.com
  - url: >-
      https://github.com/mcollina/msgpack5/security/advisories/GHSA-8hq7-ggx2-cc6m
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-8hq7-ggx2-cc6m'
tags:
  - nvd
  - ghsa
  - npm
  - cve.org
aliases:
  - GHSA-8hq7-ggx2-cc6m
ecosystem: npm
ingestedAt: '2026-10-08T17:56:11.716Z'
---

## Overview

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, constructing msgpack5 with an empty or partial options object disables the default protoAction: 'error' protection. A decoded map containing a __proto__ key can then replace the decoded object's prototype, potentially changing inherited properties or downstream behavior, although Object.prototype is not modified globally. This issue is fixed in version 6.1.0.

## Remediation

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

## Package advisory (CVE-2026-107301)

Affected packages:

- `msgpack5 < 6.1.0`

Patched in:

- `msgpack5 6.1.0`

Source: https://github.com/advisories/GHSA-8hq7-ggx2-cc6m