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Applications using the Pages Router with i18n configured and middleware/proxy-based authorization can allow unauthorized access to protected page data through locale-less /_next/data/<buildId>/<page>.json requests. In affected configurations, middleware does not run for the unprefixed data route, allowing an attacker to retrieve SSR JSON for protected pages without passing the intended authorization checks.
The matcher logic was updated to perform the same match as it would on a non-i18n data route.
If you cannot upgrade immediately, enforce authorization in the page's server-side data path instead of relying solely on middleware.
Applications using the Pages Router with i18n configured and middleware/proxy-based authorization can allow unauthorized access to protected page data through locale-less /_next/data/<buildId>/<page>.json requests. In affected configurations, middleware does not run for the unprefixed data route, allowing an attacker to retrieve SSR JSON for protected pages without passing the intended authorization checks.
The matcher logic was updated to perform the same match as it would on a non-i18n data route.
If you cannot upgrade immediately, enforce authorization in the page's server-side data path instead of relying solely on middleware.
This high-severity vulnerability could allow attackers to gain unauthorized access, execute arbitrary code, or compromise data integrity. Prompt remediation is strongly recommended.
Probability of exploitation in the next 30 days · more likely than 54.0% of all CVEs.
Apply security patches to version 15.5.16, 16.2.5 immediately
Isolate affected systems from untrusted networks until patching is complete
Implement enhanced monitoring for exploitation attempts and unusual behavior