CVE-2026-44573
HIGH7.5EPSS 0.05%Next.js has a Middleware / Proxy bypass in Pages Router applications using i18n
Description
### Impact 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. ### Fix The matcher logic was updated to perform the same match as it would on a non-i18n data route. ### Workarounds If you cannot upgrade immediately, enforce authorization in the page's server-side data path instead of relying solely on middleware.
Affected packages (1)
- npm/next>= 12.2.0, < 15.5.16
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N |