The Sniper Attack: Anonymously Deanonymizing and Disabling the Tor Network

Abstract

Abstract-Tor is a distributed onion-routing network used for achieving anonymity and resisting censorship online. Because of Tor's 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 Tor's 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 relay's memory by as much as 2187 KiB/s while using at most only 92 KiB/s 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 Tor's 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.

Locating the Source of Message Diffusion in the Anonymous Network

“…To render target clients to connect to a malicious webserver, thus revealing their IP addresses. Jansen et al [12] found an implementation error in current Tor clients. The proposed sniper attack could also find the sender in an anonymous network by exhausting the target's memory.…”

An Analysis of Active Attacks on Anonymity Systems

“…Rob Jansen, Florian Tschorsch from US Naval Research Laboratory and Aaron Johnson from Humboldt University of Berlin proposed a new denial of service attack method for Tor network, called Sniper attack [8]. The method can destroy any node of Tor.…”

Guard Sets for Onion Routing

“…We did not attempt to investigate how guard sets would cope under DoS attacks such as the Sniper Attack [13], where the intent is to simply observe more clients. We expect that guard sets may suffer more than other entry schemes if the attack is to maximize the number clients observed by the adversary.…”