Modelling and Analysis of Network Security Policies

Nowadays, computers and network communications have a pervasive presence in all our daily activities. Their correct configuration in terms of security is becoming more and more complex due to the growing number and variety of services present in a network. Generally, the security configuration of a computer network is dictated by specifying the policies of the security controls (e.g. firewall, VPN gateway) in the network. This implies that the specification of the network security policies is a crucial step to avoid errors in network configuration (e.g., blocking legitimate traffic, permitting unwanted traffic or sending insecure data). In the literature, an anomaly is an incorrect policy specification that an administrator may introduce in the network. In this thesis, we indicate as policy anomaly any conflict (e.g. two triggered policy rules enforcing contradictory actions), error (e.g. a policy cannot be enforced because it requires a cryptographic algorithm not supported by the security controls) or sub-optimization (e.g. redundant policies) that may arise in the policy specification phase. Security administrators, thus, have to face the hard job of correctly specifying the policies, which requires a high level of competence. Several studies have confirmed, in fact, that many security breaches and breakdowns are attributable to administrators’ responsibilities. Several approaches have been proposed to analyze the presence of anomalies among policy rules, in order to enforce a correct security configuration. However, we have identified two limitations of such approaches. On one hand, current literature identifies only the anomalies among policies of a single security technology (i.e., IPsec, TLS), while a network is generally configured with many technologies. On the other hand, existing approaches work on a single policy type, also named domain (i.e., filtering, communication protection). Unfortunately, the complexity of real systems is not self-contained and each network security control may affect the behavior of other controls in the same network. The objective of this PhD work was to investigate novel approaches for modelling security policies and their anomalies, and formal techniques of anomaly analysis. We present in this dissertation our contributions to the current policy analysis state of the art and the achieved results. A first contribution was the definition of a new class of policy anomalies, i.e. the inter-technology anomalies, which arises in a set of policies of multiple security technologies. We provided also a formal model able to detect these new types of anomalies. One of the results achieved by applying the inter-technology analysis to the communication protection policies was to categorize twelve new types of anomalies. The second result of this activity was derived from an empirical assessment that proved the practical significance of detecting such new anomalies. The second contribution of this thesis was the definition of a newly-defined type of policy analysis, named inter-domain analysis, which identifies any anomaly that may arise among different policy domains. We improved the state of the art by proposing a possible model to detect the inter-domain anomalies, which is a generalization of the aforementioned inter-technology model. In particular, we defined the Unified Model for Policy Analysis (UMPA) to perform the inter-domain analysis by extending the analysis model applied for a single policy domain to comprehensive analysis of anomalies among many policy domains. The result of this last part of our dissertation was to improve the effectiveness of the analysis process. Thanks to the inter-domain analysis, indeed, administrators can detect in a simple and customizable way a greater set of anomalies than the sets they could detect by running individually any other model

Applying static code analysis to firewall policies for the purpose of anomaly detection

Department Head: Bruce Austin Draper.2009 Summer.Includes bibliographical references (pages 71-74).Treating modern firewall policy languages as imperative, special purpose programming languages, in this thesis we will try to apply static code analysis techniques for the purpose of anomaly detection. We will first abstract a policy in common firewall policy language into an intermediate language, and then we will try to apply anomaly detection algorithms to it. The contributions made by this thesis are: 1. An analysis of various control flow instructions in popular firewall policy languages 2. Introduction of an intermediate firewall policy language, with emphasis on control flow constructs. 3. Application of Static Code Analysis to detect anomalies in firewall policy, expressed in intermediate firewall policy language. 4. Sample implementation of Static Code Analysis of firewall policies, expressed in our abstract language using Datalog language

Abstracting network policies

Almost every human activity in recent years relies either directly or indirectly on the smooth and efficient operation of the Internet. The Internet is an interconnection of multiple autonomous networks that work based on agreed upon policies between various institutions across the world. The network policies guiding an institution’s computer infrastructure both internally (such as firewall relationships) and externally (such as routing relationships) are developed by a diverse group of lawyers, accountants, network administrators, managers amongst others. Network policies developed by this group of individuals are usually done on a white-board in a graph-like format. It is however the responsibility of network administrators to translate and configure the various network policies that have been agreed upon. The configuration of these network policies are generally done on physical devices such as routers, domain name servers, firewalls and other middle boxes. The manual configuration process of such network policies is known to be tedious, time consuming and prone to human error which can lead to various network anomalies in the configuration commands. In recent years, many research projects and corporate organisations have to some level abstracted the network management process with emphasis on network devices (such as Cisco VIRL) or individual network policies (such as Propane). [Continues.]</div

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

Firewall Policy Diagram: Novel Data Structures and Algorithms for Modeling, Analysis, and Comprehension of Network Firewalls

Firewalls, network devices, and the access control lists that manage traffic are very important components of modern networking from a security and regulatory perspective. When computers were first connected, they were communicating with trusted peers and nefarious intentions were neither recognized nor important. However, as the reach of networks expanded, systems could no longer be certain whether the peer could be trusted or that their intentions were good. Therefore, a couple of decades ago, near the widespread adoption of the Internet, a new network device became a very important part of the landscape, i.e., the firewall with the access control list (ACL) router. These devices became the sentries to an organization's internal network, still allowing some communication; however, in a controlled and audited manner. It was during this time that the widespread expansion of the firewall spawned significant research into the science of deterministically controlling access, as fast as possible. However, the success of the firewall in securing the enterprise led to an ever increasing complexity in the firewall as the networks became more inter-connected. Over time, the complexity has continued to increase, yielding a difficulty in understanding the allowed access of a particular device. As a result of this success, firewalls are one of the most important devices used in network security. They provide the protection between networks that only wish to communicate over an explicit set of channels, expressed through the protocols, traveling over the network. These explicit channels are described and implemented in a firewall using a set of rules, where the firewall implements the will of the organization through these rules, also called a firewall policy. In small test environments and networks, firewall policies may be easy to comprehend and understand; however, in real world organizations these devices and policies must be capable of handling large amounts of traffic traversing hundreds or thousands of rules in a particular policy. Added to that complexity is the tendency of a policy to grow substantially more complex over time; and the result is often unintended mistakes in comprehending the complex policy, possibly leading to security breaches. Therefore, the need for an organization to unerringly and deterministically understand what traffic is allowed through a firewall, while being presented with hundreds or thousands of rules and routes, is imperative. In addition to the local security policy represented in a firewall, the modern firewall and filtering router involve more than simply deciding if a packet should pass through a security policy. Routing decisions through multiple network interfaces involving vendor-specific constructs such as zones, domains, virtual routing tables, and multiple security policies have become the more common type of device found in the industry today. In the past, network devices were separated by functional area (ACL, router, switch, etc.). The more recent trend has been for these capabilities to converge and blend creating a device that goes far beyond the straight-forward access control list. This dissertation investigates the comprehension of traffic flow through these complex devices by focusing on the following research topics: - Expands on how a security policy may be processed by decoupling the original rules from the policy, and instead allow a holistic understanding of the solution space being represented. This means taking a set of constraints on access (i.e., firewall rules), synthesizing them into a model that represents an accept and deny space that can be quickly and accurately analyzed. - Introduces a new set of data structures and algorithms collectively referred to as a Firewall Policy Diagram (FPD). A structure that is capable of modeling Internet Protocol version 4 packet (IPv4) solution space in memory efficient, mathematically set-based entities. Using the FPD we are capable of answering difficult questions such as: what access is allowed by one policy over another, what is the difference in spaces, and how to efficiently parse the data structure that represents the large search space. The search space can be as large as 288; representing the total values available to the source IP address (232), destination IP address (232), destination port (216), and protocol (28). The fields represent the available bits of an IPv4 packet as defined by the Open Systems Interconnection (OSI) model. Notably, only the header fields that are necessary for this research are taken into account and not every available IPv4 header value. - Presents a concise, precise, and descriptive language called Firewall Policy Query Language (FPQL) as a mechanism to explore the space. FPQL is a Backus Normal Form (Backus-Naur Form) (BNF) compatible notation for a query language to do just that sort of exploration. It looks to translate concise representations of what the end user needs to know about the solution space, and extract the information from the underlying data structures. - Finally, this dissertation presents a behavioral model of the capabilities found in firewall type devices and a process for taking vendor-specific nuances to a common implementation. This includes understanding interfaces, routes, rules, translation, and policies; and modeling them in a consistent manner such that the many different vendor implementations may be compared to each other

Dynamic Traffic Driven Architectures and Algorithms for Securing Networks

The continuous growth in the Internet's size, the amount of data traffic, and the complexity of processing this traffic gives rise to new challenges in building high performance network devices. Such an exponential growth coupledwith the increasing sophistication of attacks, is placing stringent demands on the performance of networked systems (Firewalls). These challengesrequire new designs, architecture and algorithms for the optimization of such systems.The current or classical security of present day Internet is "static" and "oblivious" to traffic dynamics in the network. Hence, there are tremendous efforts towards the design and development of several techniques and strategies to deal with the above shortcomings. Unfortunately, the current solutions have been successful in addressing only some aspects ofsecurity. However, as a whole security remains a major issue. This is primarily due to the lack of adaptation and dynamics in the design of such intrusion detection and mitigation systems.This thesis focuses on the design of architectures and algorithms for theoptimization of such networked systems, to aid not only adaptive and real-time "packet filtering' but also fast "content basedrouting (differentiated services)' in today's data-driven networks.The approach proposed involves a unique combination of algorithmic andarchitectural techniques that aims to outperform all current solutions in termsof adaptiveness, speed of operation (under attack or heavily loaded conditions) andoverall operational cost-effectiveness of such systems. The tools proposed in thisthesis also aim to offer the flexibility to include new approaches, and providethe ability to migrate or deploy additional entities for attack detection and defense