As the use and exploitation of the Internet matures, so does its need for security. Most seriously engineered Internet sites deploy firewalls and other similar techniques to restrict Internet access to limited ranges of network services.

Although the hacking community continues to search for sites and networks that are over generous with the services and the number of services enabled, increasing effort is being placed into discovering and exploiting security flaws and weaknesses available in commonly offered services, namely web-based applications.

If a company is running an e-commerce web server, the firewall will need to allow all traffic from the Internet to that server, on the standard web ports 80 and 443, in order for customers to conduct business on the site. At the same time, the firewall will be dropping any traffic aimed at network services such as Telnet and FTP. One of the shortcomings of firewalls is that they do not have the capability to analyze the network traffic they allow. A firewall receives a packet aimed for the web server on port 80 and passes that packet onto the web server according to the firewall policy set in place. This means simply that the policy says the traffic is allowed through, so the firewall allows it through.

As you can imagine, attackers have an open playground when attacking applications because even the most expensive firewall lets them do whatever they want.

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