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. It allows unauthorized access to protected routes, compromising application security.
What is Next.js Middleware Authorization Bypass?
This vulnerability exists in Next.js middleware, enabling attackers to bypass authorization. By manipulating the x-middleware-subrequest header, malicious actors can circumvent access control logic. This grants unauthorized access to routes that should be protected by middleware-based authentication or authorization checks.
Impact and Risks for your Infrastructure
The primary impact is an authentication and authorization bypass in Next.js applications. Attackers can gain unauthorized access to sensitive pages and API routes, potentially leading to data breaches, privilege escalation, or full system compromise. This directly affects data confidentiality and integrity.
Step-by-Step Mitigation Guide
To mitigate, update your Next.js application to fixed versions: 15.2.3+, 14.2.25+, 13.5.9+, or 12.3.5+. Verify the update by checking your package.json and yarn.lock/package-lock.json files. After deployment, conduct thorough regression testing to ensure middleware functions as expected.
- 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.