Next.js has a Middleware / Proxy bypass in App Router applications via segment-prefetch routes
Package
Affected versions
>= 15.2.0, < 15.5.16
>= 16.0.0, < 16.2.5
Patched versions
15.5.16
16.2.5
Description
Published to the GitHub Advisory Database
May 11, 2026
Reviewed
May 11, 2026
Published by the National Vulnerability Database
May 13, 2026
Last updated
May 14, 2026
Impact
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
.rscand 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.Fix
We now include App Router transport variants when generating middleware matchers, so middleware protections are applied consistently to those requests as well as to the normal page URL.
Workarounds
If you cannot upgrade immediately, enforce authorization in the underlying route or page logic instead of relying solely on middleware.
References