CVE-2009-0654 in Tor
Summary
by MITRE
Tor 0.2.0.28, and probably 0.2.0.34 and earlier, allows remote attackers, with control of an entry router and an exit router, to confirm that a sender and receiver are communicating via vectors involving (1) replaying, (2) modifying, (3) inserting, or (4) deleting a single cell, and then observing cell recognition errors at the exit router. NOTE: the vendor disputes the significance of this issue, noting that the product s design "accepted end-to-end correlation as an attack that is too expensive to solve."
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Analysis
by VulDB Data Team • 10/29/2018
The vulnerability described in CVE-2009-0654 affects the Tor anonymity network version 0.2.0.28 and potentially earlier versions including 0.2.0.34. This security flaw represents a significant concern for the privacy and anonymity guarantees that Tor is designed to provide to its users. The vulnerability operates through a sophisticated attack vector that leverages control over both entry and exit nodes within the Tor network, demonstrating a critical weakness in the network's resistance to traffic analysis attacks.
The technical flaw exploits the fundamental architecture of Tor by taking advantage of the network's cell-based communication system. When an attacker controls both an entry relay and an exit relay, they can manipulate individual cells passing through the network and observe the resulting cell recognition errors at the exit point. This allows the attacker to confirm communication patterns between sender and receiver through four specific methods: replaying cells to observe responses, modifying cell contents to detect changes in behavior, inserting new cells to monitor reactions, or deleting cells to identify gaps in communication sequences. The vulnerability specifically targets the cell-level recognition mechanisms that Tor uses to maintain connection integrity.
The operational impact of this vulnerability extends beyond simple traffic correlation, as it demonstrates that attackers with sufficient resources and control over network nodes can potentially de-anonymize users by establishing communication patterns that reveal the true source and destination of network traffic. This attack method represents a form of active traffic analysis that can be particularly dangerous in environments where user privacy is paramount. The fact that the vendor acknowledges this as an "accepted end-to-end correlation" attack highlights the inherent limitations of the Tor protocol's design in addressing certain types of sophisticated adversaries. According to the ATT&CK framework, this vulnerability aligns with techniques involving network traffic analysis and can be categorized under the broader concept of traffic manipulation attacks that target the fundamental assumptions of anonymity networks.
The implications of this vulnerability underscore the ongoing tension between the practical limitations of anonymity systems and the theoretical security guarantees they attempt to provide. While the vendor's assessment that the attack is "too expensive to solve" reflects the computational complexity involved in mounting such attacks, it also acknowledges that the attack surface remains a legitimate concern for security-conscious users. This vulnerability reinforces the importance of understanding that even systems designed for strong anonymity can be susceptible to sophisticated attacks when adversaries can control multiple points in the network infrastructure. The attack methodology described in CVE-2009-0654 represents a specific instance of how the design trade-offs in anonymity networks can create exploitable conditions, particularly when considering that the Tor network's architecture relies on the assumption that no single point of control can compromise the entire communication chain. This vulnerability also demonstrates the relevance of CWE-250, which deals with execution of unauthorized code or commands, as the attack involves unauthorized manipulation of network traffic through compromised relays.