CVE-2025-30218: Vercel Next.js

Medium severity, CVSS 5.9. EPSS: 0.4% chance of exploitation in the next 30 days.

Next.js is a React framework for building full-stack web applications. To mitigate CVE-2025-29927, Next.js validated the x-middleware-subrequest-id which persisted across multiple incoming requests. However, this subrequest ID is sent to all requests, even if the destination is not the same host as the Next.js application. Initiating a fetch request to a third-party within Middleware will send the x-middleware-subrequest-id to that third party. This vulnerability is fixed in 12.3.6, 13.5.10, 14.2.26, and 15.2.4.

Affected products

• Vercel Next.js: version 12.3.5 only; version 13.5.9 only; version 14.2.25 only; version 15.2.3 only

Published 2025-04-02. Last modified 2026-06-17.