CVE-2023-31125: Socket Engine.io

Medium severity, CVSS 6.5. EPSS: 1.3% chance of exploitation in the next 30 days.

Engine.IO is the implementation of transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. An uncaught exception vulnerability was introduced in version 5.1.0 and included in version 4.1.0 of the `socket.io` parent package. Older versions are not impacted. A specially crafted HTTP request can trigger an uncaught exception on the Engine.IO server, thus killing the Node.js process. This impacts all the users of the `engine.io` package, including those who use depending packages like `socket.io`. This issue was fixed in version 6.4.2 of Engine.IO. There is no known workaround except upgrading to a safe version.

Affected products

• Socket Engine.io: from 5.1.0, before 6.4.2 (fixed in 6.4.2)

Published 2023-05-08. Last modified 2026-06-17.