Next.js has a Middleware / Proxy bypass in Pages Router applications using i18n

### Impact Applications using the Pages Router with `i18n` configured and middleware/proxy-based authorization can allow unauthorized access to protected page data through locale-less `/_next/data/<buildId>/<page>.json` requests. In affected configurations, middleware does not run for the unprefixed data route, allowing an attacker to retrieve SSR JSON for protected pages without passing the intended authorization checks. ### Fix The matcher logic was updated to perform the same match as it would on a non-i18n data route. ### Workarounds If you cannot upgrade immediately, enforce authorization in the page's server-side data path instead of relying solely on middleware.

Source published

11 May 2026 15:53:51 UTC

Source modified

10 Sep 2026 03:51:04 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