At least one of an HTTP request message and an HTTP response message is intercepted. A corresponding HTTP message model includes a plurality of message model sections. A representation of the at least one of an HTTP request message and an HTTP response message is parsed into message sections in accordance with the message model sections of the HTTP message model. A plurality of security rules are bounds to the message model sections. The plurality of security rules each specify at least one action to be taken in response to a given condition, which is based, at least in part, on a corresponding given one of the message sections. The at least one of an HTTP request message and an HTTP response message is processed in accordance with the plurality of security rules. Techniques for developing rules for a web application server firewall are also provided.