CVE-2026-107301 msgpack5: Partial options disable prototype protection
Attackers can exploit prototype pollution in msgpack5 when using partial options, potentially leading to code execution or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-107301?
CVE-2026-107301 is a medium-severity unsafe deserialization vulnerability in mcollina msgpack5, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-1321
Which versions are affected by CVE-2026-107301?
2 open source packages ship an affected version, including msgpack5.
| Package | Affected | Fixed in |
|---|---|---|
msgpack5 npm | All versions | 6.1.0 |
msgpack5 npm | All versions | 6.1.0 |
How do I fix CVE-2026-107301?
Upgrade msgpack5 to 6.1.0 or later.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2026-107301 being exploited?
There is no known exploitation of CVE-2026-107301 in the wild and no public exploit code.
Sources
Also known as AZL-106857, GHSA-8hq7-ggx2-cc6m.