CVE-2026-107301
Medium
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.
SeverityMedium
CVSS6.5
Exploit probability—
ProductMsgpack5
PublishedOct 8, 2026
First seenOct 8, 2026
Weakness typeCWE-1321Prototype pollution
How to fix
Update
- msgpack56.1.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| msgpack5npm | v < 6.1.0 | 6.1.0 |
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