What is a WAF?
A WAF (Web Application Firewall) is a security layer that filters and monitors HTTP traffic to protect web applications from attacks. It defends against threats like SQL injection, cross-site scripting (XSS), and other OWASP Top 10 vulnerabilities.
How Does WAF Work?
Unlike network firewalls that operate at the transport layer, WAFs understand HTTP and inspect request content. They analyze headers, query parameters, POST bodies, and cookies against rulesets to detect malicious patterns. A WAF can block, allow, or challenge suspicious requests before they reach your application.
WAFs can be deployed as hardware appliances, server software (like ModSecurity), or cloud services (like Cloudflare WAF or AWS WAF). Cloud WAFs are the most popular for web hosting because they require no server-side configuration and provide continuously updated rulesets. They also offer rate limiting and bot detection capabilities.