Evaluating the Probability of Malicious Co-Residency in Public Clouds

We examine a system where servers can host several virtual machines in parallel and where some of the users are malicious. Arrivals and departures of both normal and malicious users are governed by random processes. The aim is to estimate the probability that a possible target will find itself sharing a server with an attacker. Two allocation policies for assigning virtual machines to servers are studied. In both cases, as well as attacks forming part of the arrival process, multiple simultaneous attacks are considered. Closed-form expressions for the desired estimates are obtained. Comparisons with simulations for purposes of validation are presented and the effect of increasing the number of available servers is illustrated.