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

Severity: medium (CVSS 5.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-08 · updated 2026-10-08
Weakness: CWE-407

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 products

mcollina msgpack5: before 6.1.0

References

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

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