application firewall definition

This definition is part of our Essential Guide: Enterprise firewall protection: Where it stands, where it's headed

An application firewall is an enhanced firewall that limits access by applications to the operating system (OS) of a computer. Conventional firewalls merely control the flow of data to and from the central processing unit (CPU), examining each packet and determining whether or not to forward it toward a particular destination. An application firewall offers additional protection by controlling the execution of files or the handling of data by specific applications.

For best performance, a conventional firewall must be configured by the user. The user must know which ports unwanted data is likely to enter or leave through. An application firewall prevents the execution of programs or DLL (dynamic link library) files which have been tampered with. Thus, even though an intruder might get past a conventional firewall and gain entry to a computer, server, or network, destructive activity can be forestalled because the application firewall does not allow any suspected malicious code to execute.

This was first published in September 2006

Next Steps

Read about the latest advancements in Web application firewall technology and learn more about deploying, managing and supporting WAFs in the enterprise. Then read our expert advice to determine if a WAF is suitable for your organization, discover the most important questions to ask before buying a WAF, and get a comparision of the best WAF products on the market.

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