What is a primary function of a web application firewall (WAF)?

A web application firewall (WAF) primarily functions to enhance the security of web applications by applying a set of rules to HTTP conversations. This process is essential for identifying and mitigating common web-based attacks, such as SQL injection, cross-site scripting (XSS), and other vulnerabilities that target web applications. By analyzing incoming requests and ensuring they adhere to established security policies, a WAF helps protect sensitive data and maintain the integrity of the application.

In contrast, monitoring traffic based on stateful connections pertains more to traditional firewalls that manage the state of active connections and enforce security policies based on the state and context of network traffic. Detecting viruses in email messages falls outside the scope of a WAF, as that task is typically handled by dedicated email security solutions. Examining header data for authorized access might be a function of a different security mechanism, such as an access control system or an authentication gateway, rather than the central role of a WAF. Thus, the correct choice emphasizes the proactive role of a WAF in the prevention of application layer threats.