WAF

Problem

A firewall allows HTTPS: TCP 443 ✓ But an HTTP request itself might contain an attack. At the network layer, both legitimate and malicious requests simply look like HTTPS traffic.

Solution — Web Application Firewall

A WAF understands web traffic and can inspect HTTP-level patterns. Examples include SQL injection attempts such as ' OR 1=1-- in a form field, injected scripts such as <script>…</script>, and paths containing ../../ that try to reach restricted files.

HTTPS
  ↓
WAF
  ↓ inspect HTTP
Application

Core idea: a WAF applies security controls using application-layer knowledge.