{"id":"CVE-2026-107301","aliases":["GHSA-8hq7-ggx2-cc6m"],"url":"https://o3.security/vulnerability/CVE-2026-107301","summary":"msgpack5: Partial options disable prototype protection","details":"### Impact\n\nPassing an empty or partial options object disables the default `protoAction: 'error'` protection. A map containing a `__proto__` key can then replace the prototype of the decoded object, potentially changing inherited properties or causing unexpected behavior in downstream code.\n\nOnly the decoded object's prototype is affected; this does not modify `Object.prototype` globally.\n\n### Patches\n\nOptions are now merged with secure defaults without modifying the caller's object. Unsupported `protoAction` values are rejected.\n\n### Workarounds\n\nExplicitly set `protoAction: 'error'` whenever constructing a msgpack5 instance, and validate decoded values before use.","published":"2026-10-08T17:13:00.613Z","modified":"2026-10-21T02:54:36.471045765Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"msgpack5","fixedVersion":"6.1.0"}],"fix":{"url":"https://github.com/mcollina/msgpack5/commit/20e82600ac9462e679c8a45e5723315f21e2c774","label":"mcollina/msgpack5@20e8260"},"references":[{"type":"WEB","url":"https://github.com/mcollina/msgpack5/releases/tag/v6.1.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107301.json"},{"type":"ADVISORY","url":"https://github.com/mcollina/msgpack5/security/advisories/GHSA-8hq7-ggx2-cc6m"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-107301"},{"type":"FIX","url":"https://github.com/mcollina/msgpack5/commit/20e82600ac9462e679c8a45e5723315f21e2c774"},{"type":"PACKAGE","url":"https://github.com/mcollina/msgpack5"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:54:36.471045765Z"}}