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.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | msgpack5 | < 6.1.0 | 6.1.0 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L- Weakness (CWE)
CWE-1321- Platform
- npm
- Package
msgpack5- Disclosed
- 08.10.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-8hq7-ggx2-cc6m - CC BY 4.0
Vulnerability history: msgpack5
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 8
- First → latest
- 03.2021 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
- Medium 5
- Low 1
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 7
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