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Charon/docs/features/waf.md
GitHub Actions 3169b05156 fix: skip incomplete system log viewer tests
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Web Application Firewall (WAF) Protect against OWASP Top 10 vulnerabilities with Coraza WAF

Web Application Firewall (WAF)

Stop common attacks like SQL injection, cross-site scripting (XSS), and path traversal before they reach your applications. Powered by Coraza, the WAF protects your apps from the OWASP Top 10 vulnerabilities.

Overview

The Web Application Firewall inspects every HTTP/HTTPS request and blocks malicious payloads before they reach your backend services. Charon uses Coraza, a high-performance, open-source WAF engine compatible with the OWASP Core Rule Set (CRS).

Protected attack types include:

  • SQL Injection — Blocks database manipulation attempts
  • Cross-Site Scripting (XSS) — Prevents script injection attacks
  • Path Traversal — Stops directory traversal exploits
  • Remote Code Execution — Blocks command injection
  • Zero-Day Exploits — CRS updates provide protection against newly discovered vulnerabilities

Why Use This

  • Defense in Depth — Add a security layer in front of your applications
  • OWASP CRS — Industry-standard ruleset trusted by enterprises
  • Low Latency — Coraza processes rules efficiently with minimal overhead
  • Flexible Modes — Choose between monitoring and active blocking

Configuration

Enabling WAF

  1. Navigate to Proxy Hosts
  2. Edit or create a proxy host
  3. In the Security tab, toggle Web Application Firewall
  4. Select your preferred mode

Operating Modes

Mode Behavior Use Case
Monitor Logs threats but allows traffic Testing rules, reducing false positives
Block Actively blocks malicious requests Production protection

Recommendation: Start in Monitor mode to review detected threats, then switch to Block mode once you're confident in the rules.

Per-Host Configuration

WAF can be enabled independently for each proxy host:

  • Enable for public-facing applications
  • Disable for internal services or APIs with custom security
  • Mix modes across different hosts as needed

Zero-Day Protection

The OWASP Core Rule Set is regularly updated to address:

  • Newly discovered CVEs
  • Emerging attack patterns
  • Bypass techniques

Charon includes the latest CRS version and receives updates through container image releases.

Limitations

The WAF protects HTTP and HTTPS traffic only:

Traffic Type Protected
HTTP/HTTPS Proxy Hosts Yes
TCP/UDP Streams No
Non-HTTP protocols No

For TCP/UDP protection, use CrowdSec or network-level firewalls.

Troubleshooting

Issue Solution
Legitimate requests blocked Switch to Monitor mode and review logs
High latency Check if complex rules are triggering; consider rule tuning
WAF not activating Verify the proxy host has WAF enabled in Security tab