WAF Inspection Logic
Defending the Application Layer
Beyond the Port Number
A Web Application Firewall (WAF) sits between external traffic and the application servers. Unlike a Layer 3 firewall that blocks IPs, a WAF operates at Layer 7 (Application Layer). It parses the HTTP/HTTPS payload to understand exactly what the client is asking for.
WAF INSPECTION PIPELINE
L7 Logic-Based Pattern Matching (OWASP Protection)
Pattern Matching & Core Rule Sets
WAFs primarily use a combination of Negative Security (blocking known bad patterns) and Positive Security (allowing only known good patterns). The most common standard is the OWASP Core Rule Set (CRS), written for ModSecurity.
For example, a rule might look for the string ' OR 1=1 in a URL query parameter—a classic SQL injection signature.
The Challenge of False Positives
The biggest challenge in WAF engineering isn't blocking hackers—it's not blocking legitimate users. If your WAF rules are too aggressive, a user trying to write a comment with the word "SELECT" might be blocked. This requires continuous tuning and the use of "Log-Only" mode for new rules.
By integrating WAF logic into your API Gateway or CDN edge, you shift the defensive perimeter as far away from your database as possible.