An application firewall is a specialized cybersecurity control designed to protect web applications and APIs by monitoring, filtering, and controlling data traffic at the application layer (Layer 7) of the OSI model. Unlike traditional network firewalls that inspect IP addresses and ports at lower network layers, application firewalls possess deep contextual awareness of application-specific protocols such as HTTP/S, XML, and JSON. This enables them to analyze the actual content, payload, and logic of communications to identify malicious patterns and attack attempts.

Application firewalls serve as a critical defense mechanism against sophisticated application-layer threats including SQL injection, cross-site scripting (XSS), broken authentication, and denial-of-service attacks. By performing deep packet inspection and enforcing customized security policies, they prevent malicious requests from exploiting vulnerabilities in web applications. Their primary purpose is to safeguard sensitive data, ensure application availability, and strengthen an organization's overall security posture against evolving cyber threats.