CVE-2026-40299
JavaScript vulnerability analysis and mitigation

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 next-intl@4.9.1.

Credits

Many thanks to Joni Liljeblad from Oura for responsibly disclosing the vulnerability and for suggesting the fix.


SourceNVD

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CVE ID

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Score

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Component name

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Has fix

Published date

GHSA-68qg-g8mg-6pr7CRITICAL10
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CVE-2026-40299MEDIUM6.9
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