Vulnerability · Published Oct 8, 2026 · Assigned by GitHub_M

CVE-2026-107297msgpack5: Quadratic parsing in the streaming decoder

Medium 5.9

In plain English

A medium-severity security flaw in msgpack5 from mcollina. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 33% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium

Exploit odds (30 days)0.4%top 66.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder reparses an incomplete array or map from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack container across many small chunks, causing completed elements to be decoded repeatedly, producing quadratic CPU use and blocking the event loop. This issue is fixed in version 6.1.0.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	msgpack5	6.1.0	GHSA-gcx5-hxj7-gpqq

Affected products (as reported)

Vendor	Product	Versions
mcollina	msgpack5	< 6.1.0

Weakness: CWE-407 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/mcollina/msgpack5/security/advisories/GHSA-gcx5-hxj7-gpqq x_refsource_CONFIRM
https://github.com/mcollina/msgpack5/commit/e4827641d3105e295cbbd56e9c5389978547eab4 x_refsource_MISC
https://github.com/mcollina/msgpack5/releases/tag/v6.1.0 x_refsource_MISC