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Computer Sciences, telecommunications
At present, the recommended stance to take regarding Cyber Security is to assume a state of compromise. With the increase in Bring Your Own Device (BYOD), the Internet of Things (IOT) and Advanced Persistent Threats (ATPs), network boundaries have become porous and difficult to defend from external threats. Modern malware is complex and adept at making its presence hard to detect. Recent studies have shown that some malware variants are capable of using multiple covert communication channels for command and control (C2) and data exfiltration activities. Examples of this level of covert communication can be found in malware that targets Point of Sale (POS) systems and it has been hugely successful in exfiltrating large amounts of valuable payment information that can be sold on the black market. In the vast majority of cases, malware needs to communicate with some control mechanism or human controller in order to coordinate attacks, maintain lists of compromised machines and to exfiltrate data. There are many channels that malware can use for its communication. However, in recent times there has been an increase in malware that uses the Domain Name System (DNS) for communications in some shape or form. The work carried out in this paper explores the extent to which DNS can be used as a covert communication channel by examining a number of advanced approaches that can be used to increase the stealthy nature of DNS-based covert channels. Our work describes techniques that can be used to shadow legitimate network traffic by observing network packets leaving a host machine (piggybacking), the use of statistical modelling such as the Poisson distribution and a dynamic Poisson distribution model that can be used to further conceal malicious DNS activity within a network. The results obtained from this work show that current DNS-based C2 and data exfiltration approaches employed by malware have considerable room for improvement which suggests that DNS-based covert communication will remain a realistic threat into the future.
Sheridan, S. & Keane, A. (2017) Improving the Stealthiness of DNS-Based Covert Communication,16th European Conference on Cyber Warfare and Security, 29-30 June 2017, Dublin, Ireland