CVE-2006-3416 in Tor
Summary
by MITRE
** DISPUTED ** Tor before 0.1.1.20 kills the circuit when it receives an unrecognized relay command, which causes network circuits to be disbanded. NOTE: while this item is listed under the "Security fixes" section of the developer changelog, the developer clarified on 20060707 that this is only a self-DoS. Therefore this issue should not be included in CVE.
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Analysis
by VulDB Data Team • 08/07/2024
The vulnerability described in CVE-2006-3416 relates to an issue within the Tor anonymization network software version 0.1.1.19 and earlier. This flaw represents a self-denial of service condition where the Tor software terminates network circuits upon receiving unrecognized relay commands. The vulnerability operates at the protocol level within the Tor network infrastructure, specifically affecting how relay nodes handle malformed or unexpected command sequences. When a relay node encounters a command that it does not recognize, the system is designed to terminate the circuit rather than gracefully handle the unexpected input, leading to disruption of network connectivity.
From a technical perspective, this vulnerability demonstrates a lack of proper error handling within the Tor relay implementation. The system's response to unrecognized commands is overly aggressive, resulting in complete circuit termination instead of implementing more graceful degradation mechanisms. This behavior aligns with CWE-248, which addresses "Uncaught Exception" conditions where programs fail to handle exceptional circumstances properly. The flaw essentially creates a scenario where malicious actors or system errors could cause legitimate network circuits to be destroyed, though the vulnerability is classified as self-DoS since it affects the Tor software itself rather than external adversaries.
The operational impact of this vulnerability, while limited in scope due to its self-DoS nature, could still cause significant disruption to network reliability and user experience. When circuits are terminated unexpectedly, users may experience connection failures or reduced anonymity service availability. The vulnerability affects the stability of the Tor network by creating unnecessary disruptions in the communication pathways between nodes. Network administrators and users would observe intermittent connection issues as circuits are repeatedly disbanded due to the handling of unrecognized commands. This issue particularly impacts the robustness of the Tor network's infrastructure and could contribute to overall network instability during periods of high traffic or when encountering malformed data packets.
Security practitioners should note that while this vulnerability does not represent a direct security threat to user anonymity or network confidentiality, it does demonstrate poor defensive programming practices that could be exploited in combination with other vulnerabilities. The issue highlights the importance of implementing proper error handling and graceful degradation mechanisms in network infrastructure software. Although the vulnerability has been disputed and removed from official CVE listings, it serves as an example of how seemingly minor implementation flaws can impact network reliability. The Tor development team's clarification that this is a self-DoS vulnerability aligns with ATT&CK technique T1499.004, which covers "Evasion: File System Weaving" and related denial of service conditions that can be triggered by malformed input processing. Organizations should ensure that their network infrastructure implements robust input validation and error handling to prevent similar issues from affecting system stability and availability.