msgpack5: Partial options disable prototype protection

中 6.5CVE-2026-107301 · GHSA-8hq7-ggx2-cc6m · 08/10/2026 公開 · 14/10/2026 更新

要点

CVE-2026-107301 は msgpack5 に影響する深刻度「中」 (CVSS 6.5) の脆弱性です。
今後30日間に悪用される確率（EPSS）：0.37%（全脆弱性の 30.7% より高い）。
対処：6.1.0 以降に更新してください。

パッケージ	影響を受けるバージョン	修正済みバージョン
msgpack5 npm	`< 6.1.0`	`6.1.0`

概要

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.

NVD の説明

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.