Tran, Tung2009-02-202009-02-202009-02-202009-02-16http://hdl.handle.net/10012/4285Network access control (NAC) systems have a very important role in network security. However, NAC policy configuration is an extremely complicated and error-prone task due to the semantic complexity of NAC policies and the large number of rules that could exist. This significantly increases the possibility of policy misconfigurations and network vulnerabilities. NAC policy misconfigurations jeopardize network security and can result in a severe consequence such as reachability and denial of service problems. In this thesis, we choose to study and analyze the NAC policy configuration of two significant network security devices, namely, firewall and IDS/IPS. In the first part of the thesis, a visualization technique is proposed to visualize firewall rules and policies to efficiently enhance the understanding and inspection of firewall configuration. This is implemented in a tool called PolicyVis. Our tool helps the user to answer general questions such as ‘‘Does this policy satisfy my connection/security requirements’’. If not, the user can detect all misconfigurations in the firewall policy. In the second part of the thesis, we study various policy misconfigurations of Snort, a very popular IDS/IPS. We focus on the misconfigurations of the flowbits option which is one of the most important features to offers a stateful signature-based NIDS. We particularly concentrate on a class of flowbits misconfiguration that makes Snort susceptible to false negatives. We propose a method to detect the flowbits misconfiguration, suggest practical solutions with controllable false positives to fix the misconfiguration and formally prove that the solutions are complete and sound.enfirewallintrusion detection systemMaster ThesisComputer Science