What Do Firewalls Protect? an Empirical Study of Firewalls, Vulnerabilities, and Attacks

Firewalls are a cornerstone of how sites implement "Defense in depth." Many security policies assume that outside attackers must first penetrate a firewall configured to block their access. This paper examines what firewalls protect against, and whether those protections are sufficient to warrant placing the current level of trust in firewalls. Individuals and corporations build multiple layers of security mechanisms to protect their computers. They use firewalls, intrusion detection systems, virus scanners, and other protective software, and these mechanisms provide some level of assurance that the security policies for the site are properly implemented. An active system administration staff, knowledgeable about security, adds to this assurance.