Mitigating Mimicry Attacks Against the Session Initiation Protocol

The U.S. National Academies of Science\´s Board on Science, Technology and Economic Policy estimates that the Internet and voice-over-IP (VoIP) communications infrastructure generates 10% of U.S. economic growth. As market forces move increasingly towards Internet and VoIP communications, there is proportional increase in telephony denial of service (TDoS) attacks. Like denial of service (DoS) attacks, TDoS attacks seek to disrupt business and commerce by directing a flood of anomalous traffic towards key communication servers. In this work, we focus on a new class of anomalous traffic that exhibits a mimicry TDoS attack. Such an attack can be launched by crafting malformed messages with small changes from normal ones. We show that such malicious messages easily bypass intrusion detection systems (IDS) and degrade the goodput of the server drastically by forcing it to parse the message looking for the needed token. Our approach is not to parse at all; instead, we use multiple classifier systems (MCS) to exploit the strength of multiple learners to predict the true class of a message with high probability (98.50% ≤ p ≤ 99.12%). We proceed systematically by first formulating an optimization problem of picking the minimum number of classifiers such that their combination yields the optimal classification performance. Next, we analytically bound the maximum performance of such a system and empirically demonstrate that it is possible to attain close to the maximum theoretical performance across varied datasets. Finally, guided by our analysis we construct an MCS appliance that demonstrates superior classification accuracy with runtime complexity across varied datasets.