How to fix CVE-2025-29927 – Step-by-Step Guide
CVE-2025-29927, named 'Next.js Middleware Authorization Bypass', is a critical vulnerability (CVSS 9.1) affecting Next.js applications. This flaw allows unauthorized access to protected routes, posing a significant security risk.
What is Next.js Middleware Authorization Bypass?
This vulnerability in Next.js middleware enables attackers to bypass authorization checks. By manipulating the x-middleware-subrequest header, malicious actors can trick the application into granting unauthorized access. This circumvents intended access controls, allowing direct access to restricted resources.
Impact and Risks for your Infrastructure
The primary impact is a severe authentication and authorization bypass. Attackers can gain unauthorized access to sensitive pages, API routes, and data without valid credentials. This can lead to data breaches, unauthorized actions, and compromise of application integrity.
Step-by-Step Mitigation Guide
To mitigate CVE-2025-29927, upgrade your Next.js application immediately to a patched version: 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+. Verify the fix by ensuring your middleware correctly enforces authorization for all routes, even with manipulated x-middleware-subrequest headers.
- 1Upgrade Next.js immediately to 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+.
- 2Block x-middleware-subrequest header at CDN/reverse proxy level.
- 3Move critical authorization checks from middleware into route handlers/server components.
- 4Audit all middleware.ts files for security-critical authorization logic.
- 5Deploy Cloudflare WAF rule or equivalent to block the header manipulation.
- 6Rotate session tokens and audit access logs for potential exploitation.