CVE-2026-44573: vercel next.js Incorrect Authorization

Vulnerability summary

CVE-2026-44573 is a high (CVSS 7.5) Incorrect Authorization vulnerability in vercel next.js. EPSS estimates a 0.76% chance of exploitation in the next 30 days, higher than 54.7% of scored vulnerabilities.

Timeline

1. 13-05-2026
   PublishedVulnerability first disclosed.
2. 13-08-2026
   Last modifiedVulnerability information updated.

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.

• CWE-863Incorrect AuthorizationThe product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
• CWE-551Incorrect Behavior Order: Authorization Before Parsing and CanonicalizationIf a web server does not fully parse requested URLs before it examines them for authorization, it may be possible for an attacker to bypass authorization protection.