CVE-2026-40299
next-intl has an open redirect vulnerability
Description
### Impact Applications using the `next-intl` middleware 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. ### Patches The problem has been patched, please update to [`[email protected]`](https://github.com/amannn/next-intl/releases/tag/v4.9.1). ### Credits Many thanks to [Joni Liljeblad](https://github.com/joniumGit) from [Oura](https://ouraring.com) for responsibly disclosing the vulnerability and for suggesting the fix.
How to fix CVE-2026-40299
To remediate CVE-2026-40299, upgrade the affected package to a fixed version below.
- —upgrade to 4.9.1 or later
Is CVE-2026-40299 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- from 0, < 4.9.1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N |