Authentication Bypass Using an Alternate Path or Channel

Summary

Next.js is a React framework for building full-stack web applications. In versions 15.2.0 prior to 15.5.16 and 16.0.0 prior to 16.2.5, App Router applications that rely on middleware or proxy-based checks for authorization can allow unauthorized access through transport-specific route variants used for segment prefetching. In affected configurations, specially crafted .rsc and segment-prefetch URLs can resolve to the same page without being matched by the intended middleware rule, which can allow protected content to be reached without the expected authorization check. This vulnerability is fixed in 15.5.16 and 16.2.5.