vercel next.js: CVE-2025-29927: (Improper Authorization)

Next.js is a React framework for building full-stack web applications. Prior to 14.2.25 and 15.2.3, it is possible to bypass authorization checks within a Next.js application, if the authorization check occurs in middleware. This check is exploit based and as a result runs a get request against a series of URIs (/admin, /dashboard, /settings, /account, /profile) and checks for a redirect request (response code 307) that would suggest a login is required. We then attempt to use the x-middleware-subrequest to bypass this login requirement which can be observed in the request returning a 200 response code.