CVE-2007-4099 in Tor
Summary
by MITRE
Tor before 0.1.2.15 can select a guard node beyond the first listed never-before-connected-to guard node, which allows remote attackers with control of certain guard nodes to obtain sensitive information and possibly leverage further attacks.
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Analysis
by VulDB Data Team • 09/06/2018
The vulnerability identified as CVE-2007-4099 affects the Tor anonymity network version 0.1.2.15 and earlier, exposing a critical flaw in the network's guard node selection mechanism. This issue specifically relates to how Tor clients choose their initial guard nodes, which are critical components in maintaining anonymity by serving as the first hop in the circuit. The vulnerability allows attackers who control certain guard nodes to potentially compromise user anonymity and access sensitive information. The flaw stems from the client's algorithm for selecting guard nodes, which incorrectly permits the selection of guard nodes beyond the first listed never-before-connected-to guard node in the configuration.
The technical implementation of this vulnerability involves the Tor client's guard node selection process where the software fails to properly enforce the principle of selecting only the first available guard node from a list of candidates. This behavior creates a scenario where malicious actors who control guard nodes can manipulate the network traffic flow and potentially correlate user activities. The vulnerability specifically impacts the network's resistance to traffic analysis attacks and allows for more sophisticated surveillance operations. According to CWE standards, this represents a weakness in the security model related to improper enforcement of access control policies. The flaw directly violates fundamental anonymity principles by enabling adversaries to gain information about user behavior and potentially identify users through traffic correlation attacks.
The operational impact of this vulnerability extends beyond simple information disclosure to encompass broader security implications for the entire Tor network. Attackers with control over guard nodes can leverage this weakness to perform more effective traffic analysis, potentially de-anonymizing users by observing patterns in network traffic. This vulnerability creates a pathway for advanced persistent threats to compromise the anonymity guarantees that Tor is designed to provide. The attack surface is particularly concerning because guard nodes are fundamental to the network's architecture, making them attractive targets for adversaries seeking to undermine anonymity. From an ATT&CK framework perspective, this vulnerability maps to techniques involving traffic analysis and network monitoring, specifically targeting the network infrastructure components that are essential for maintaining user privacy.
Mitigation strategies for this vulnerability require immediate upgrades to Tor client versions beyond 0.1.2.15 where the guard node selection algorithm was corrected to properly enforce the selection of only the first available guard node. Network administrators and users should ensure they are running patched versions of the Tor software, as the vulnerability was addressed through changes to the client's guard node selection logic. The fix implemented in later versions enforces stricter rules for guard node selection, preventing the problematic behavior that allowed attackers to select non-first guard nodes. Organizations should also implement monitoring for unusual network behavior that might indicate guard node compromise, though the primary defense remains software updates. This vulnerability highlights the critical importance of maintaining up-to-date anonymity tools and demonstrates how seemingly minor implementation flaws in security systems can have significant implications for user privacy and security. The incident underscores the necessity of rigorous security testing for anonymity networks and proper enforcement of access control mechanisms in privacy-preserving systems.