Server Security Testing: Nginx Proxy

TL;DR

Testing a server behind an nginx proxy requires checking both the server itself and how nginx handles traffic. This guide covers vulnerability scanning, penetration testing, and configuration reviews for both layers.

1. Understand Your Setup

Before you start, know your environment:

• Server OS: (e.g., Linux, Windows)
• Server Software: (e.g., Apache, Node.js, databases)
• Nginx Configuration: Where is it located? What virtual hosts are defined?
• Network Topology: How does traffic flow to the server? Are there firewalls involved?

2. Server-Side Security Testing

Treat your server as if nginx wasn’t there – it’s still a target.

1. Vulnerability Scanning: Use tools like Nessus, OpenVAS, or Nikto to identify known vulnerabilities.

   nikto -h <server_ip>

2. Penetration Testing: Manually test for common web application attacks (SQL injection, XSS, CSRF) and OS-level exploits. Tools like Metasploit can help.

   Consider using a framework like OWASP ZAP to automate some of the testing.

3. Configuration Review: Check server configurations for insecure settings (e.g., default passwords, unnecessary services).
   • Disable unused ports and services.
   • Ensure strong password policies are in place.
   • Keep software up to date with the latest security patches.
4. Log Analysis: Review server logs for suspicious activity.

3. Nginx Security Testing

Nginx acts as a gatekeeper, so its security is crucial.

1. Configuration Review: Examine your nginx configuration file (usually nginx.conf) for potential issues.
   • SSL/TLS Configuration: Use tools like SSL Labs Server Test (https://www.ssllabs.com/ssltest/) to check your certificate and protocol settings.
   • Access Control: Verify that access control lists (ACLs) are correctly configured to restrict unwanted traffic.
   • Caching Configuration: Ensure caching isn’t exposing sensitive data.
   • Proxy Settings: Check how nginx is proxying requests to the backend server. Avoid passing unnecessary headers.

     proxy_pass http://backend_server;

2. Denial of Service (DoS) Testing: Simulate DoS attacks to see how nginx handles high traffic loads. Tools like hping3 can be used.

   Be careful with this – you could disrupt service!

3. HTTP Header Injection: Test if it’s possible to inject malicious headers through Nginx.
4. Reverse Proxy Vulnerabilities: Look for vulnerabilities specific to reverse proxies, such as HTTP smuggling.

4. Testing Through the Proxy

Test your application as if you were a user going through nginx.

1. Web Application Firewall (WAF) Bypass: If you’re using a WAF, try to bypass it with various payloads and techniques.
2. End-to-End Penetration Testing: Perform a full penetration test from the user’s perspective, going through nginx to reach the server.

   This will reveal any vulnerabilities that might be missed when testing each layer separately.

5. Automation

Automate as much of this process as possible:

• Regular Vulnerability Scans: Schedule scans to run automatically on a regular basis.
• Configuration Management: Use tools like Ansible or Chef to ensure consistent and secure configurations.
• Continuous Integration/Continuous Deployment (CI/CD) Pipeline: Integrate security testing into your CI/CD pipeline.