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.
{
"cna_assigner": "GitHub_M",
"cwe_ids": [
"CWE-601"
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40299.json"
}{
"extracted_events": [
{
"range": [
{
"introduced": "0"
},
{
"fixed": "4.9.1"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StringRangeExpression"
},
{
"range": [
{
"fixed": "1c80b668aa6d853f470319eec10a3f61e78a70e6"
}
],
"source": "REFERENCES_COMMIT"
},
{
"original_tag": "v4.9.1",
"range": [
{
"fixed": "b4aa5380c50ad59a80d1dfdbc229590a4e0133a3"
}
],
"source": "REFERENCES_TAG"
}
]
}