The Sniper Attack: Anonymously Deanonymizing and Disabling the Tor Network
OFFICE OF NAVAL RESEARCH ARLINGTON VA
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Tor is a distributed onion-routing network used for achieving anonymity and resisting censorship online. Because of Tors growing popularity, it is attracting increasingly larger threats against which it was not securely designed. In this paper we present the Sniper Attack, an extremely low cost but highly destructive denial of service attack against Tor that an adversary may use to anonymously disable arbitrary Tor relays. The attack utilizes valid protocol messages to boundlessly consume memory by exploiting Tors end-to-end reliable data transport. We design and evaluate a prototype of the attack to show its feasibility and efficiency our experiments show that an adversary may consume a victim relays memory by as much as 2187 KiBs while using at most only 92 KiBs of upstream bandwidth. We extend our experimental results to estimate the threat against the live Tor network and find that a strategic adversary could disable all of the top 20 exit relays in only 29 minutes, thereby reducing Tors bandwidth capacity by 35 percent. We also show how the attack enables the deanonymization of hidden services through selective denial of service by forcing them to choose guard nodes in control of the adversary. Finally, we discuss defenses against the Sniper Attack that provably render the attack ineffective, and suggest defenses against deanonymization by denial-of-service attacks in general that significantly mitigate the threat.
- Computer Systems Management and Standards