CVE-2026-40299

Description

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 `[email protected]`.

EPSS — Exploit Prediction

0.0005

Probability of exploitation

0.17%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-601 CWE-601

References

Other References

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

Frequently Asked Questions

What is 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 `[email protected]`.

How do I check if I'm vulnerable to CVE-2026-40299? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2024-53995

SickChill is an automatic video library manager for TV shows. A user-controlled `login` endpoint's `next_` parameter takes arbitrary content. Prior …

CVE-2026-3318

Open redirection vulnerability in the latest demo version of the Cradle eCommerce platform. The vulnerability occurs in the login form …

CVE-2026-42350

Kargo manages and automates the promotion of software artifacts. Prior to versions 1.7.10, 1.8.13, 1.9.8, and 1.10.2, Kargo is vulnerable …

CVE-2025-25300

smartbanner.js is a customizable smart app banner for iOS and Android. Prior to version 1.14.1, clicking on smartbanner `View` link …

CVE-2025-46826

insa-auth is an authentication server for INSA Rouen. A minor issue allowed third-party websites to access the server's secondary authentication …

CVE-2025-40846

Improper Input Validation, the returnUrl parameter in Account Security Settings lacks proper input validation, allowing attackers to redirect users to …