6.3. Web Application Firewall

A simple HTTP request that looks like ?id=1; DROP TABLE users-- can destroy your database. SQL injection, cross-site scripting (XSS), and protocol violations slip right past network firewalls because they're hidden inside legitimate-looking HTTP requests. WAF protects web applications by understanding these attacks.

💡 First Principle: WAF operates at Layer 7, inspecting HTTP/HTTPS traffic content. Think of it like a customs officer who doesn't just check your passport—they search your luggage for contraband. WAF understands web attacks: not just suspicious IPs or ports, but malicious payloads inside legitimate-looking requests.

What breaks without WAF:

• SQL injection attacks compromise your database
• XSS attacks steal user sessions
• Automated scanners find and exploit vulnerabilities
• Compliance requirements for web application security go unmet

Consider where WAF fits in your architecture: Azure Firewall protects at the network layer (Layer 3-4), while WAF protects at the application layer (Layer 7). For web applications, you typically want both—Azure Firewall for network threats, WAF for application threats.