Next.js has a Middleware / Proxy bypass in App Router applications via segment-prefetch routes

### 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 `.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. ### 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.

Source published

11 May 2026 15:54:24 UTC

Source modified

10 Sep 2026 03:51:03 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Publisher rating · HIGH