CVE-2026-40299 next-intl has an open redirect vulnerability
Attackers can redirect users to malicious sites via crafted URLs when using specific locale prefix configurations in next-intl middleware.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40299?
CVE-2026-40299 is a medium-severity vulnerability in amannn next-intl, published on 17 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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]`.
Weakness: CWE-601
Which versions are affected by CVE-2026-40299?
2 open source packages ship an affected version, including next-intl.
| Package | Affected | Fixed in |
|---|---|---|
next-intl npm | All versions | 4.9.1 |
next-intl npm | All versions | 4.9.1 |
How do I fix CVE-2026-40299?
Upgrade next-intl to 4.9.1 or later.
Is CVE-2026-40299 being exploited?
There is no known exploitation of CVE-2026-40299 in the wild and no public exploit code.
Sources
Also known as GHSA-8f24-v5vv-gm5j.