What’s Vulnerable › Vulnerabilities

CVE-2026-40299: next-intl has an open redirect vulnerability

• Severity: medium (CVSS 6.9 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-17 · updated 2026-10-26
• Weakness: CWE-601

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 `next-intl@4.9.1`.

Affected products

• amannn next-intl: before 4.9.1

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

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