CVE-2006-3418 in Tor
Summary
by MITRE
Tor before 0.1.1.20 does not validate that a server descriptor s fingerprint line matches its identity key, which allows remote attackers to spoof the fingerprint line, which might be trusted by users or other applications.
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Analysis
by VulDB Data Team • 07/31/2018
The vulnerability described in CVE-2006-3418 represents a critical flaw in the Tor anonymity network's server descriptor validation mechanism. This issue affects Tor versions prior to 0.1.1.20 and fundamentally undermines the trust model that the network relies upon for maintaining user anonymity and network integrity. The vulnerability stems from insufficient cryptographic validation within the server descriptor processing logic, creating a pathway for malicious actors to manipulate critical network metadata.
The technical flaw specifically involves the absence of validation between the fingerprint line and the identity key within server descriptors. In proper cryptographic systems, server descriptors contain both a fingerprint that should match the identity key and the actual identity key itself. When this validation is missing, attackers can craft server descriptors where the fingerprint line contains false information while the actual identity key remains valid. This creates a scenario where the network's trust infrastructure becomes compromised, as the fingerprint serves as a cryptographic identifier that users and other applications rely upon to verify server authenticity.
The operational impact of this vulnerability extends beyond simple spoofing capabilities to potentially enable sophisticated attacks against the Tor network's integrity. Attackers could exploit this weakness to create false server descriptors that appear legitimate to users and applications, leading to potential traffic redirection, man-in-the-middle attacks, or the compromise of user anonymity. The vulnerability particularly affects the network's ability to maintain a consistent and trustworthy directory of servers, as the fingerprint validation mechanism that should provide cryptographic assurance becomes ineffective. This weakness could enable attackers to impersonate legitimate Tor servers and potentially intercept or manipulate traffic flowing through the network.
Mitigation strategies for this vulnerability require immediate upgrade to Tor version 0.1.1.20 or later, which implements proper fingerprint validation against identity keys. Organizations and users should also implement additional monitoring mechanisms to detect anomalous server descriptor changes and establish redundant verification processes. From a cybersecurity perspective, this vulnerability aligns with CWE-224, which addresses improper validation of security-critical information, and relates to ATT&CK technique T1566 for social engineering attacks that exploit trust relationships. The fix implemented in subsequent versions demonstrates the importance of cryptographic validation in distributed systems and highlights the critical need for proper certificate and fingerprint validation in anonymity networks. Network administrators should also consider implementing additional layers of authentication and validation beyond the basic Tor protocol to maintain security posture against similar vulnerabilities.