Publications

Defense in depth is a common strategy that uses layers of firewalls to protect Supervisory Control and Data Acquisition (SCADA) subnets and other critical resources on enterprise networks. A tool named NetSPA is presented that analyzes firewall rules and vulnerabilities to construct attack graphs. These show how inside and outside attackers can progress by successively compromising exposed vulnerable hosts with the goal of reaching critical internal targets. NetSPA generates attack graphs and automatically analyzes them to produce a small set of prioritized recommendations to restore defense in depth. Field trials on networks with up to 3,400 hosts demonstrate that firewalls often do not provide defense in depth due to misconfigurations and critical unpatched vulnerabilities on hosts. In all cases, a small number of recommendations was provided to restore defense in depth. Simulations on networks with up to 50,000 hosts demonstrate that this approach scales well to enterprise-size networks.

Assessing the security of large enterprise networks is complex and labor intensive. Current security analysis tools typically examine only individual firewalls, routers, or hosts separately and do not comprehensively analyze overall network security. We present a new approach that uses configuration information on firewalls and vulnerability information on all network devices to build attack graphs that show how far inside and outside attackers can progress through a network by successively compromising exposed and vulnerable hosts. In addition, attack graphs are automatically analyzed to produce a small set of prioritized recommendations to enhance network security. Field trials on networks with up to 3,400 hosts demonstrate the ability to accurately identify a small number of critical stepping-stone hosts that need to be patched to protect against external attackers. Simulation studies on complex networks with more than 40,000 hosts demonstrate good scaling. This analysis can be used for many purposes, including identifying critical stepping-stone hosts to patch or protect with a firewall, comparing the security of alternating network designs, determining the security risk caused by proposed changes in firewall rules or new vulnerabilities, and identifying the most critical hosts to patch when a new vulnerability is announced. Unique aspects of this work are new attack graph generation algorithms that scale to enterprise networks with thousands of hosts, efficient approaches to determine what other hosts and ports in large networks are reachable from each individual host, automatic data importation from network vulnerability scanners and firewalls, and automatic attack graph analyses to generate recommendations.