Flow Reconnaissance via Timing Attacks on SDN Switches
Sheng Liu, Michael Reiter and Vyas Sekar
University of North Carolina at Chapel Hill, University of North Carolina at Chapel Hill, Carnegie Mellon University

When encountering a packet flow for which it has no covering rule, a software-defined networking (SDN) switch requests an appropriate rule from its controller; this request delays the routing of the flow until the controller responds. We show that this delay gives rise to a timing side channel in which an attacker can test for the recent occurrence of a target flow by judiciously probing the switch with forged flows and using the delays they suffer to discern whether covering rules were previously installed in the switch. We develop a Markov model of an SDN switch to permit the attacker to select the best probe (or probes) to infer whether a target flow has recently occurred. Our model captures complexities related to rule evictions to make room for other rules; rule timeouts due to inactivity; the presence of multiple rules that apply to overlapping sets of flows; and rule priorities. We show that our model permits detection of target flows with considerable accuracy in many cases.