CVE-2026-107301: medium-severity vulnerability in mcollina msgpack5
msgpack5: Partial options disable prototype protection
Published
10Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 6.5
exploitation probability
—
observed exploitation
nono source reports it
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.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L
Affected products
mcollina · msgpack5Related CVEs — mcollina msgpack5
In the same product, most dangerous first.
CVE-2021-21368MEDIUMPrototype poisoningEPSS 1.6%CVE-2026-107302HIGHmsgpack5: Truncated map32 headers throw an unexpected errorEPSS —CVE-2026-107300HIGHmsgpack5: Many buffered values can exhaust the streaming decoder stackEPSS —CVE-2026-107299MEDIUMmsgpack5: Reserved byte can cause unbounded stream bufferingEPSS —CVE-2026-107298MEDIUMmsgpack5: Deeply nested input can exhaust the decoder stackEPSS —CVE-2026-107297MEDIUMmsgpack5: Quadratic parsing in the streaming decoderEPSS —