Directed Acyclic Graph Modeling of Security Policies for Firewall Testing

Abstract

IntroductionFirewalls, which act as the most important defense mechanism of network security, have to be tested to validate that they work as specified. The firewall specification is mainly composed of intended security policy and allowed network protocols, which are usually the main focus of an attacker. The intended security policy consists of firewall rules, which configure the firewall behavior, and allowed network protocols. These constitute an important part of firewall's internal infrastructure which can be described as packet capture, decision making on the packet under consideration, and packet release. Decision making operation is carried out with respect to firewall policy and network protocols. The security policy is external to the firewall like a configuration file, whereas packet checking with respect to network protocols is implemented in the firewall software.Since the firewall policy is considered as a specification and can be represented by a formal model, we propose a model-based testing approach for firewalls. The novelty of this approach is using DAG model for firewall testing. This paper proposes modeling of firewall rules and generating test cases using DAGs. Since event sequence graphs (ESG) are directed graphs, we applied its test case generation algorithm to the DAG representation of firewall rules. Then test packets derived from generated test cases are sent to the firewall to analyze its behavior.Next section summarizes related work before Section 3 outlines background and the test generation algorithm. The core of the paper, Section 4, presents our firewall testing approach. Sections 5 and 6 include implementation details of the approach and a case study on a firewall. Section 7 concludes the paper and outlines our research work planned. Related WorkA firewall controls network traffic to and from a computer, based on a security policy. Although systematic testing was an omitted area in firewall studies and relative literature, recent studies on

Modeling Firewalls for Behavior Analysis

“…Model-based conformance testing by 11 involves experiments with the experiment size of 7 rules generating over 700 test cases taking about 3000 seconds, and 4 networks adding an additional 20,000 seconds. A test case generation tool presented in 12 indicates that the number of tests generated is a cross product of the number of individual sources, destinations, and services found in the rule set, suggesting a much higher complexity when using this brute force method. Furthermore, experiments in 13 show similar results when using a BDD as an internal representation of the policy, although the work was focused on model checking and not simulation.…”

“…Frameworks capable of generating validation traffic for a particular firewall presented in several works 23,12 . In a similar manner to other topology mapping programs 24,25 , the work generates and sends actual traffic through the system, exercising a firewall's internal filtering to ensure consistency.…”

Towards Measuring Test Coverage of Attack Simulations

“…In a proposal for testing of security policies for firewalls, the security policies were represented as directed acyclic graphs (DAGs). Test cases represented each complete event sequence which could be derived from the DAG [27]. System testing and code-based coverage analysis employ similar testing methodologies.…”

Mutation-Based Evaluation of Weighted Test Case Selection for Firewall Testing

“…In this work, we use FDD [9] notion for modeling, whereas in our previous work [10], we used directed acyclic graph concept to deal with rule dependencies, which is implicitly handled by FDD. The present paper chooses FDD notation since formal, graph-theoretical notions and algorithms are utilized intensively with it.…”