Medium severity · published Oct 8, 2026
CVE-2026-107301
msgpack5: Partial options disable prototype protection
6.5
CVSS
0.4%
EPSS
No
On KEV
Description
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 vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
None
Integrity
High
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 30% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MS
msgpack5 · mcollina
< 6.1.0 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-107301
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-107301
x_refsource_CONFIRM
https://github.com/mcollina/msgpack5/security/advisories/GHSA-8hq7-ggx2-cc6m
x_refsource_MISC
https://github.com/mcollina/msgpack5/commit/20e82600ac9462e679c8a45e5723315f21e2c774
x_refsource_MISC
https://github.com/mcollina/msgpack5/releases/tag/v6.1.0
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