Formal Firewall Conformance Testing: An Application of Test and Proof Techniques

Firewalls are an important means to secure critical ICT infrastructures. As configurable off-the-shelf prod\-ucts, the effectiveness of a firewall crucially depends on both the correctness of the implementation itself as well as the correct configuration. While testing the implementation can be done once by the manufacturer, the configuration needs to be tested for each application individually. This is particularly challenging as the configuration, implementing a firewall policy, is inherently complex, hard to understand, administrated by different stakeholders and thus difficult to validate. This paper presents a formal model of both stateless and stateful firewalls (packet filters), including NAT, to which a specification-based conformance test case gen\-eration approach is applied. Furthermore, a verified optimisation technique for this approach is presented: starting from a formal model for stateless firewalls, a collection of semantics-preserving policy transformation rules and an algorithm that optimizes the specification with respect of the number of test cases required for path coverage of the model are derived. We extend an existing approach that integrates verification and testing, that is, tests and proofs to support conformance testing of network policies. The presented approach is supported by a test framework that allows to test actual firewalls using the test cases generated on the basis of the formal model. Finally, a report on several larger case studies is presented

Applying Formal Methods to Networking: Theory, Techniques and Applications

Despite its great importance, modern network infrastructure is remarkable for the lack of rigor in its engineering. The Internet which began as a research experiment was never designed to handle the users and applications it hosts today. The lack of formalization of the Internet architecture meant limited abstractions and modularity, especially for the control and management planes, thus requiring for every new need a new protocol built from scratch. This led to an unwieldy ossified Internet architecture resistant to any attempts at formal verification, and an Internet culture where expediency and pragmatism are favored over formal correctness. Fortunately, recent work in the space of clean slate Internet design---especially, the software defined networking (SDN) paradigm---offers the Internet community another chance to develop the right kind of architecture and abstractions. This has also led to a great resurgence in interest of applying formal methods to specification, verification, and synthesis of networking protocols and applications. In this paper, we present a self-contained tutorial of the formidable amount of work that has been done in formal methods, and present a survey of its applications to networking.Comment: 30 pages, submitted to IEEE Communications Surveys and Tutorial

Traffic generator for firewall testing

Thesis (Master)--Izmir Institute of Technology, Computer Engineering, Izmir, 2009Includes bibliographical references (leaves: 52-56)Text in English; Abstract: Turkish and Englishix, 92 leavesFirewalls lead at the front line of a computer network to restrict unauthorized access. The desired security level is determined by a policy and implemented by a firewall which not only has to be effective but also stable and reliable service is expected. In order to verify the level of security of the system, testing is required. The objective of this thesis is to test a firewall with software testing techniques taking into consideration the nominated policy and the firewall. Iptables software was examined and tested by two different algorithms that were modified according to software testing techniques, and the results were observed. Packets sent through the Firewall Under Test (FUT) are compared to packets passed through the FUT and test results were observed. The security performance of the modified algorithms proved to be successful

Handling Stateful Firewall Anomalies

Part 4: Access ControlInternational audienceA security policy consists of a set of rules designed to protect an information system. To ensure this protection, the rules must be deployed on security components in a consistent and non-redundant manner. Unfortunately, an empirical approach is often adopted by network administrators, to the detriment of theoretical validation. While the literature on the analysis of configurations of first generation (stateless) firewalls is now rich, this is not the case for second and third generation firewalls, also known as stateful firewalls. In this paper, we address this limitation, and provide solutions to analyze and handle stateful firewall anomalies and misconfiguration

Model-Based Development of firewall rule sets: Diagnosing model inconsistencies

The design and management of firewall rule sets is a very difficult and error-prone task because of the difficulty of translating access control requirements into complex low-level firewall languages. Although high-level languages have been proposed to model firewall access control lists, none has been widely adopted by the industry. We think that the main reason is that their complexity is close to that of many existing low-level languages. In addition, none of the high-level languages that automatically generate firewall rule sets verifies the model prior to the code-generation phase. Error correction in the early stages of the development process is cheaper compared to the cost associated with correcting errors in the production phase. In addition, errors generated in the production phase usually have a huge impact on the reliability and robustness of the generated code and final system. In this paper, we propose the application of the ideas of Model-Based Development to firewall access control list modelling and automatic rule set generation. First, an analysis of the most widely used firewall languages in the industry is conducted. Next, a Platform-Independent Model for firewall ACLs is proposed. This model is the result of exhaustive analysis and of a discussion of different alternatives for models in a bottom-up methodology. Then, it is proposed that a verification stage be added in the early stages of the Model-Based Development methodology, and a polynomial time complexity process and algorithms are proposed to detect and diagnose inconsistencies in the Platform-Independent Model. Finally, a theoretical complexity analysis and empirical tests with real models were conducted, in order to prove the feasibility of our proposal in real environments

Global Verification and Analysis of Network Access Control Configuration

Network devices such as routers, firewalls, IPSec gateways, and NAT are configured using access control lists. However, recent studies and ISP surveys show that the management of access control configurations is a highly complex and error prone task. Without automated global configuration management tools, unreachablility and insecurity problems due to the misconfiguration of network devices become an ever more likely. In this report, we present a novel approach that models the global end-to-end behavior of access control devices in the network including routers, firewalls, NAT, IPSec gateways for unicast and multicast packets. Our model represents the network as a state machine where the packet header and location determine the state. The transitions in this model are determined by packet header information, packet location, and policy semantics for the devices being modeled. We encode the semantics of access control policies with Boolean functions using binary decision diagrams (BDDs). We extended computation tree logic (CTL) to provide more useful operators and then we use CTL and symbolic model checking to investigate all future and past states of this packet in the network and verify network reachability and security requirements. The model is implemented in a tool called ConfigChecker. We gave special consideration to ensure an efficient and scalable implementation. Our extensive evaluation study with various network and policy sizes shows that ConfigChecker has acceptable computation and space requirements with large number of nodes and configuration rules

Automated optimal firewall orchestration and configuration in virtualized networks

Emerging technologies such as Software-Defined Networking and Network Functions Virtualization are making the definition and configuration of network services more dynamic, thus making automatic approaches that can replace manual and error-prone tasks more feasible. In view of these considerations, this paper proposes a novel methodology to automatically compute the optimal allocation scheme and configuration of virtual firewalls within a user-defined network service graph subject to a corresponding set of security requirements. The presented framework adopts a formal approach based on the solution of a weighted partial MaxSMT problem, which also provides good confidence about the solution correctness. A prototype implementation of the proposed approach based on the z3 solver has been used for validation, showing the feasibility of the approach for problem instances requiring tens of virtual firewalls and similar numbers of security requirements