CVE-2026-40299
CVE-2026-40299 is a medium-severity vulnerability with a CVSS 4.0 base score of 6.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-601.
Key facts
- Severity: Medium (CVSS 4.0 base score 6.9)
- EPSS exploit prediction: 0% (26th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-23543
- Weakness: CWE-601
- Published:
- Last modified:
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]`.
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 severe is CVE-2026-40299?
- CVE-2026-40299 has a CVSS 4.0 base score of 6.9, rated medium severity.
- Is CVE-2026-40299 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (26th percentile), an estimate of the probability of exploitation in the next 30 days.
- How do I fix CVE-2026-40299?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-40299 have an EU (EUVD) identifier?
- Yes. CVE-2026-40299 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-23543.
- When was CVE-2026-40299 published?
- CVE-2026-40299 was published on 2026-04-17 and last updated on 2026-06-17.
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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