Directed Security Policies: A Stateful Network Implementation

Large systems are commonly internetworked. A security policy describes the communication relationship between the networked entities. The security policy defines rules, for example that A can connect to B, which results in a directed graph. However, this policy is often implemented in the network, for example by firewalls, such that A can establish a connection to B and all packets belonging to established connections are allowed. This stateful implementation is usually required for the network's functionality, but it introduces the backflow from B to A, which might contradict the security policy. We derive compliance criteria for a policy and its stateful implementation. In particular, we provide a criterion to verify the lack of side effects in linear time. Algorithms to automatically construct a stateful implementation of security policy rules are presented, which narrows the gap between formalization and real-world implementation. The solution scales to large networks, which is confirmed by a large real-world case study. Its correctness is guaranteed by the Isabelle/HOL theorem prover.Comment: In Proceedings ESSS 2014, arXiv:1405.055

Packet flow analysis in IP networks via abstract interpretation

Static analysis (aka offline analysis) of a model of an IP network is useful for understanding, debugging, and verifying packet flow properties of the network. There have been static analysis approaches proposed in the literature for networks based on model checking as well as graph reachability. Abstract interpretation is a method that has typically been applied to static analysis of programs. We propose a new, abstract-interpretation based approach for analysis of networks. We formalize our approach, mention its correctness guarantee, and demonstrate its flexibility in addressing multiple network-analysis problems that have been previously solved via tailor-made approaches. Finally, we investigate an application of our analysis to a novel problem -- inferring a high-level policy for the network -- which has been addressed in the past only in the restricted single-router setting.Comment: 8 page

Automated Approaches for Program Verification and Repair

Formal methods techniques, such as verification, analysis, and synthesis,allow programmers to prove properties of their programs, or automatically derive programs from specifications. Making such techniques usable requires care: they must provide useful debugging information, be scalable, and enable automation. This dissertation presents automated analysis and synthesis techniques to ease the debugging of modular verification systems and allow easy access to constraint solvers from functional code. Further, it introduces machine learning based techniques to improve the scalability of off-the-shelf syntax-guided synthesis solvers and techniques to reduce the burden of network administrators writing and analyzing firewalls. We describe the design and implementationof a symbolic execution engine, G2, for non-strict functional languages such as Haskell. We extend G2 to both debug and automate the process of modular verification, and give Haskell programmers easy access to constraints solvers via a library named G2Q. Modular verifiers, such as LiquidHaskell, Dafny, and ESC/Java,allow programmers to write and prove specifications of their code. When a modular verifier fails to verify a program, it is not necessarily because of an actual bug in the program. This is because when verifying a function f, modular verifiers consider only the specification of a called function g, not the actual definition of g. Thus, a modular verifier may fail to prove a true specification of f if the specification of g is too weak. We present a technique, counterfactual symbolic execution, to aid in the debugging of modular verification failures. The approach uses symbolic execution to find concrete counterexamples, in the case of an actual inconsistency between a program and a specification; and abstract counterexamples, in the case that a function specification is too weak. Further, a counterexample-guided inductive synthesis (CEGIS) loop based technique is introduced to fully automate the process of modular verification, by using found counterexamples to automatically infer needed function specifications. The counterfactual symbolic execution and automated specification inference techniques are implemented in G2, and evaluated on existing LiquidHaskell errors and programs. We also leveraged G2 to build a library, G2Q, which allows writing constraint solving problemsdirectly as Haskell code. Users of G2Q can embed specially marked Haskell constraints (Boolean expressions) into their normal Haskell code, while marking some of the variables in the constraint as symbolic. Then, at runtime, G2Q automatically derives values for the symbolic variables that satisfy the constraint, and returns those values to the outside code. Unlike other constraint solving solutions, such as directly calling an SMT solver, G2Q uses symbolic execution to unroll recursive function definitions, and guarantees that the use of G2Q constraints will preserve type correctness. We further consider the problem of synthesizing functions viaa class of tools known as syntax-guided synthesis (SyGuS) solvers. We introduce a machine learning based technique to preprocess SyGuS problems, and reduce the space that the solver must search for a solution in. We demonstrate that the technique speeds up an existing SyGuS solver, CVC4, on a set of SyGuS solver benchmarks. Finally, we describe techniques to ease analysis and repair of firewalls.Firewalls are widely deployed to manage network security. However, firewall systems provide only a primitive interface, in which the specification is given as an ordered list of rules. This makes it hard to manually track and maintain the behavior of a firewall. We introduce a formal semantics for iptables firewall rules via a translation to first-order logic with uninterpreted functions and linear integer arithmetic, which allows encoding of firewalls into a decidable logic. We then describe techniques to automate the analysis and repair of firewalls using SMT solvers, based on user provided specifications of the desired behavior. We evaluate this approach with real world case studies collected from StackOverflow users

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

A demonstration of VEREFOO: an automated framework for virtual firewall configuration

Nowadays, security automation exploits the agility characterizing network virtualization to replace the traditional error-prone human operations. This dynamism allows user-specified high-level intents to be rapidly refined into the concrete configuration rules which should be deployed on virtual security functions. In this revolutionary context, this paper proposes the demonstration of a novel security framework based on an optimized approach for the automatic orchestration of virtual distributed firewalls. The framework provides formal guarantees for the firewall configuration correctness and minimizes the size of the firewall allocation scheme and rule set. The framework produces rules that can be deployed on multiple types of real virtual function implementations, such as iptables, eBPF firewalls and Open vSwitch

Hyp3rArmor: reducing web application exposure to automated attacks

Web applications (webapps) are subjected constantly to automated, opportunistic attacks from autonomous robots (bots) engaged in reconnaissance to discover victims that may be vulnerable to specific exploits. This is a typical behavior found in botnet recruitment, worm propagation, largescale fingerprinting and vulnerability scanners. Most anti-bot techniques are deployed at the application layer, thus leaving the network stack of the webapp’s server exposed. In this paper we present a mechanism called Hyp3rArmor, that addresses this vulnerability by minimizing the webapp’s attack surface exposed to automated opportunistic attackers, for JavaScriptenabled web browser clients. Our solution uses port knocking to eliminate the webapp’s visible network footprint. Clients of the webapp are directed to a visible static web server to obtain JavaScript that authenticates the client to the webapp server (using port knocking) before making any requests to the webapp. Our implementation of Hyp3rArmor, which is compatible with all webapp architectures, has been deployed and used to defend single and multi-page websites on the Internet for 114 days. During this time period the static web server observed 964 attempted attacks that were deflected from the webapp, which was only accessed by authenticated clients. Our evaluation shows that in most cases client-side overheads were negligible and that server-side overheads were minimal. Hyp3rArmor is ideal for critical systems and legacy applications that must be accessible on the Internet. Additionally Hyp3rArmor is composable with other security tools, adding an additional layer to a defense in depth approach.This work has been supported by the National Science Foundation (NSF) awards #1430145, #1414119, and #1012798

Sistema open-source de alta-disponibilidade de segurança de redes

Due to the growing number of cyber-attacks and the overall digital world knowledge, there is an urgent need to improve cyber security systems. Some of the measures implemented in these systems use network monitoring systems. This document regards a security system with a similar approach focused on prevention and reaction to a shortage of service. It is an Open-Source solution aiming to prevent DDoS attacks and adapt a network to realtime failures through smart configurations of security devices like Firewalls and Load-Balancers. The system is capable of periodically monitoring the state of the devices, as well as reconfiguring routing policies and packet filtering rules in scenarios of cyber attacks. Moreover, it provides an interface of interaction with the network admin to deliver data regarding the state of the security equipment and the connection between them, enhancing traffic flow analysis and preventive implementation of traffic filtering rules in Firewalls. As for technologies, these changes in the machines were designed to be implemented in IPTables and NFTables to be compatible with most Linux distributions. The monitoring and reconfiguration process was automated with Python scripts and SSH connections. The whole testing scenario was developed while being simulated with GNS3 and Virtualbox, interacting with a physical computer hosting the system. All functionalities defined along the document were tested and showed positive results.Atualmente, devido ao crescente número de ataques informáticos e conhecimento geral do mundo digital, existe uma necessidade urgente de aprimorar medidas de segurança informática. Algumas destas medidas passam por implementar mecanismos de monitorização da rede. Esta dissertação aborda um sistema de segurança que implementa um mecanismo semelhante, com capacidade de prevenção e reação a possíveis falhas. Foca-se na implementação de uma solução Open-Source com vista a prevenir ataques DDoS e adaptar uma rede a dificuldades vividas em realtime, através de configurações inteligentes de equipamento de segurança como Load-Balancers e Firewalls. O sistema é capaz de monitorizar periodicamente o estado destas máquinas, bem como reconfigurar poltíticas de encaminhamento e regras de filtro de tráfego em cenários de falha de funcionamento de equipamento devido a ciber ataques. Mais ainda, providencia uma interface de interação com o administrador de rede para fornecer dados acerca de cada máquina e das ligações que constituem a infrastrutura de segurança, potenciando uma análise dos fluxos de tráfego e aplicação de regras de filtragem em Firewalls. No que toca a tecnologias, foram preparadas configurações tanto em IPTables como NFTables, com vista a ser compatível com o maio número de distribuições de Linux possível. O processo de monitorização e a implementação novas regras é automatizado através da linguagem Python e ligações SSH. O cenário de testes foi simulado em máquinas virtuais através dos softwares VirtualBox e GNS3, interagindo com o sistema implementado num computador real, e todas as funcionalidades definidas ao longo do documento poderam ser testadas com resultados positivos.Mestrado em Engenharia de Computadores e Telemátic