msgpack5: Partial options disable prototype protection

### Impact Passing 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. Only the decoded object's prototype is affected; this does not modify `Object.prototype` globally. ### Patches Options are now merged with secure defaults without modifying the caller's object. Unsupported `protoAction` values are rejected. ### Workarounds Explicitly set `protoAction: 'error'` whenever constructing a msgpack5 instance, and validate decoded values before use.

Source published

8 Oct 2026 17:39:57 UTC

Source modified

8 Oct 2026 18:00:08 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L

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