CVE-2025-30218 – Next.js may leak x-middleware-subrequest-id to external hosts

https://notcve.org/view.php?id=CVE-2025-30218

02 Apr 2025 — 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... • https://github.com/vercel/next.js/security/advisories/GHSA-223j-4rm8-mrmf • CWE-200: Exposure of Sensitive Information to an Unauthorized Actor •