CVE-2026-107301CWE-1321

CVE-2026-107301

Medium · published October 8, 2026

CVSS v3.1
6.5
EPSS
0%
Percentile
29.3
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
6.5 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L
CVSS v4.0
Not supplied
EPSS
0.00366 · 29.3th percentile
Weakness
CWE-1321 · Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Published
2026-10-08T21:17Z
References (3)
https://github.com/mcollina/msgpack5/commit/20e82600ac9462e679c8a45e5723315f21e2c774 · [email protected]https://github.com/mcollina/msgpack5/releases/tag/v6.1.0 · [email protected]https://github.com/mcollina/msgpack5/security/advisories/GHSA-8hq7-ggx2-cc6m · [email protected]
EPSS history
Timeline
  • 10 OCT 03:27Z
    EPSS moved — → 0%
    epss
  • 08 OCT 17:13Z
    msgpack5: Partial options disable prototype protection
    cvelistv5
  • 08 OCT 17:13Z
    msgpack5: Partial options disable prototype protection
    cvelistv5