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Vulnerability · Published May 13, 2026 · Assigned by GitHub_M

CVE-2026-44573Next.js: Middleware / Proxy bypass in Pages Router applications using i18n

High 7.5

In plain English

A high-severity incorrect authorization in next.js from vercel. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.8% (higher than 57% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.8%top 43.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

Next.js is a React framework for building full-stack web applications. From 12.2.0 to before 15.5.16 and 16.2.5, 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. This vulnerability is fixed in 15.5.16 and 16.2.5.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
npmnext15.5.16GHSA-36qx-fr4f-26g5
npmnext16.2.5GHSA-36qx-fr4f-26g5

Affected products (as reported)

VendorProductVersions
vercel next.js >= 12.2.0, < 15.5.16>= 16.0.0, < 16.2.5

Weakness: CWE-863, CWE-551 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

References