CVE Catalog

CVE-2026-40299

MediumCVSS 6.9
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.34%

27th percentile - higher than 27% of all known CVEs

Summary

Applications using the next-intl middleware prior to version 4.9.1 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.

Risk Assessment

An attacker can exploit the open redirect for phishing and credential theft by abusing trust in the application's domain. The risk applies to Next.js applications using next-intl with the specified configuration.

Recommendation

Update next-intl to version 4.9.1 or later. Review the localePrefix configuration and verify redirect logic in the middleware.

Related vulnerabilities

Original NVD description (English source)

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]`.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS