Next.js has a Middleware / Proxy bypass in Pages Router applications using i18n
Published 11 May 2026 · Updated 10 Sept 2026
Affected packages
- Affected
- >=12.2.0 <15.5.16
- Fixed in
- 15.5.16
npm install next@15.5.16- Affected
- >=16.0.0 <16.2.5
- Fixed in
- 16.2.5
npm install next@16.2.5Details
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.
Is GHSA-36qx-fr4f-26g5 in any of your client repos?
Checking one package by hand is fine. Checking it across forty client projects is not. NPMscan reads the lockfiles in every GitHub repo you pick, finds each project with an affected next, and gives you the command that fixes it.
References
Advisory data from OSV.dev (opens OSV.dev in a new tab), refreshed daily.