A Web Application Firewall (WAF) is a security solution that monitors, filters and blocks HTTP/HTTPS traffic between the internet and a web application to protect against common web-based attacks. It operates at the application layer (Layer 7 of the OSI model) and can defend against threats such as SQL injection, cross-site scripting (XSS), file inclusion and other OWASP Top 10 vulnerabilities. WAFs can be deployed as hardware appliances, software solutions or cloud-based services.
Deploying a WAF provides an important layer of defence for web applications, particularly when rapid patching of application vulnerabilities is not feasible. Modern WAFs offer adaptive rule sets, bot detection and API protection capabilities that go beyond traditional signature-based filtering. However, a WAF should complement, not replace, secure coding practices and regular vulnerability assessments as part of a defence-in-depth strategy.