On Robust Covert Channels Inside DNS
- Cite this paper as:
- Nussbaum L., Neyron P., Richard O. (2009) On Robust Covert Channels Inside DNS. In: Gritzalis D., Lopez J. (eds) Emerging Challenges for Security, Privacy and Trust. SEC 2009. IFIP Advances in Information and Communication Technology, vol 297. Springer, Berlin, Heidelberg
Covert channels inside DNS allow evasion of networks which only provide a restricted access to the Internet. By encapsulating data inside DNS requests and replies exchanged with a server located outside the restricted network, several existing implementations provide either an IP over DNS tunnel, or a socket-like service (TCP over DNS). This paper contributes a detailed overview of the challenges faced by the design of such tunnels, and describes the existing implementations. Then, it introduces TUNS, our prototype of an IP over DNS tunnel, focused on simplicity and protocol compliance. Comparison of TUNS and the other implementations showed that this approach is successful: TUNS works on all the networks we tested, and provides reasonable performance despite its use of less efficient encapsulation techniques, especially when facing degraded network conditions.