Abstract-By accurately measuring risk for enterprise networks, attack graphs allow network defenders to understand the most critical threats and select the most effective countermeasures. This paper describes substantial enhancements to the NetSPA attack graph system required to model additional present-day threats (zero-day exploits and client-side attacks) and countermeasures (intrusion prevention systems, proxy firewalls, personal firewalls, and host-based vulnerability scans). Point-to-point reachability algorithms and structures were extensively redesigned to support "reverse" reachability computations and personal firewalls. Host-based vulnerability scans are imported and analyzed. Analysis of an operational network with 85 hosts demonstrates that client-side attacks pose a serious threat. Experiments on larger simulated networks demonstrated that NetSPA's previous excellent scaling is maintained. Less than two minutes are required to completely analyze a four-enclave simulated network with more than 40,000 hosts protected by personal firewalls.

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Abstract. We revisit the problem of memory checking considered by Blum et al. [3]. In this model, a checker monitors the behavior of a data structure residing in unreliable memory given an arbitrary sequence of user defined operations. The checker is permitted a small amount of separate reliable memory and must fail a data structure if it is not behaving as specified and pass it otherwise. How much additional reliable memory is required by the checker? First, we present a checker for an implementation of a priority queue. The checker uses O( √ n log n) space where n is the number of operations performed. We then present a spotchecker using only O( −1 log δ −1 log n) space, that, with probability at least 1 − δ, will fail the priority queue if it is -far (defined appropriately) from operating like a priority queue and pass the priority queue if it operates correctly. Finally, we then prove a range of lower bounds that complement our checkers.