medium6.9
CVE-2026-40299
next-intl provides internationalization for Next.js.
Impact
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`.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| npm | next-intl | < 4.9.1 | 4.9.1 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/amannn/next-intl/commit/1c80b668aa6d853f470319eec10a3f61e78a70e6
- https://github.com/amannn/next-intl/pull/2304
- https://github.com/amannn/next-intl/releases/tag/v4.9.1
- https://github.com/amannn/next-intl/security/advisories/GHSA-8f24-v5vv-gm5j
- https://github.com/advisories/GHSA-8f24-v5vv-gm5j
- https://nvd.nist.gov/vuln/detail/CVE-2026-40299