No abstract

Even well administered networks are vulnerable to attack. Recent work in network security has focused on the fact that combinations of exploits are the typical means by which an attacker breaks into a network. Researchers have proposed a variety of graph-based algorithms to generate attack trees (or graphs). Either structure represents all possible sequences of exploits, where any given exploit can take advantage of the penetration achieved by prior exploits in its chain, and the final exploit in the chain achieves the attacker's goal. The most recent approach in this line of work uses a modified version of the model checker NuSMV as a powerful inference engine for chaining together network exploits, compactly representing attack graphs, and identifying minimal sets of exploits. However, it is also well known that model checkers suffer from scalability problems, and there is good reason to doubt whether a model checker can handle directly a realistic set of exploits for even a modestsized network. In this paper, we revisit the idea of attack graphs themselves, and argue that they represent more information explicitly than is necessary for the analyst. Instead, we propose a more compact and scalable representation. Although we show that it is possible to produce attack trees from our representation, we argue that more useful information can be produced, for larger networks, while bypassing the attack tree step. Our approach relies on an explicit assumption of monotonicity, which, in essence, states that the precondition of a given exploit is never invalidated by the successful application of another exploit. In other words, the attacker never needs to backtrack. The assumption reduces the complexity of the analysis problem from exponential to polynomial, thereby bringing even very large networks within reach of analysis.

No abstract

Abstract. The extensible access control markup language (XACML) is the standard access control policy specification language of the World Wide Web. XACML does not provide exclusive accesses to globally resources. We do so by enhancing the policy execution framework with locks.

In this paper we identify an undesirable side-effect of combining different email-control mechanisms for protection from unwanted messages, namely, leakage of recipients' private information to message senders. The problem arises because some email-control mechanisms like bonds, graph-turing tests, etc., inherently leak information, and without discontinuing their use, leakage channels cannot be closed. We formalize the capabilities of an attacker and show how she can launch guessing attacks on recipient's mail acceptance policy that utilizes leaky mechanism in an effort to avoid unwanted mail. The attacker in our model guesses the contents of a recipient's private information. The recipients' use of leaky mechanisms allow the sender to verify her guess. We assume a constraint logic programming based policy language for specification and evaluation of mail acceptance criteria and present two different program transformations that can prevent guessing attacks while allowing recipients to utilize any email-control mechanism in their policies.