Web-application firewalls (WAF) filter and block nonessential traffic at the application layer.
Used in conjunction with a network-based firewall, a properly configured web-application firewall prevents application-layer attacks if applications are improperly coded or configured. This can be achieved through a combination of technology and process. Process-based solutions must have mechanisms that facilitate timely responses to alerts in order to meet the intent of this requirement, which is to prevent attacks.