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EUVD-2026-292073

fkie_cve-2026-40299

next-intl provides internationalization for Next.js. Applications using the `next-intl` middleware prior to version 4.9.1with `localePrefix: 'as-needed'` could construct URLs where path handling and the WHATWG URL parser resolved a relative redirect target to another host (e.g. scheme-relative `//` or control characters stripped by the URL parser), so the middleware could redirect the browser off-site while the user still started from a trusted app URL. The problem has been patchedin `next-intl@4.9.1`.

GHSA-8f24-v5vv-gm5j — next-intl has an open redirect vulnerability

Affected: npm: next-intl

### Impact

Applications using the `next-intl` middleware with `localePrefix: 'as-needed'` could construct URLs where path handling and the WHATWG URL parser resolved a relative redirect target to another host (e.g. scheme-relative `//` or control characters stripped by the URL parser), so the middleware could redirect the browser off-site while the user still started from a trusted app URL.

### Patches

The problem has been patched, please update to [`next-intl@4.9.1`](https://github.com/amannn/next-intl/releases/tag/v4.9.1).

### Credits

Many thanks to [Joni Liljeblad](https://github.com/joniumGit) from [Oura](https://ouraring.com) for responsibly disclosing the vulnerability and for suggesting the fix.