CVE-2012-3519 in Tor
Summary
by MITRE
routerlist.c in Tor before 0.2.2.38 uses a different amount of time for relay-list iteration depending on which relay is chosen, which might allow remote attackers to obtain sensitive information about relay selection via a timing side-channel attack.
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Analysis
by VulDB Data Team • 04/12/2021
The vulnerability described in CVE-2012-3519 resides within the Tor anonymization network's routerlist.c component, specifically affecting Tor versions prior to 0.2.2.38. This issue represents a timing side-channel attack vector that exploits the inconsistent execution time patterns during relay list iteration processes. The flaw manifests when the Tor client performs relay selection operations, where the time required to process different relays varies significantly based on the specific relay being evaluated. This temporal variation creates a measurable difference that remote attackers can potentially exploit to infer information about the relay selection algorithm and underlying network topology.
The technical implementation of this vulnerability stems from how Tor's routerlist.c module handles relay iteration operations. When processing relay lists for network selection, the system exhibits variable timing behavior that correlates with the specific relay characteristics being examined. This timing inconsistency occurs because the relay selection logic does not maintain constant execution time regardless of which relay is being processed, creating a predictable pattern that can be observed through timing measurements. The vulnerability directly relates to CWE-385, which addresses timing side-channel attacks where attackers can extract information based on the time taken to execute specific operations. The implementation flaw violates the principle of constant-time execution that is essential for cryptographic and security-sensitive operations.
From an operational perspective, this vulnerability poses significant risks to the anonymity and security of Tor network users. Remote attackers who can monitor network timing characteristics can potentially reconstruct information about relay selection patterns and network topology, thereby compromising the anonymity guarantees that Tor provides. The attack vector allows adversaries to perform relay selection inference attacks, which could lead to deanonymization of users by identifying specific relays or network paths. This timing-based information leakage represents a sophisticated threat that operates at the network protocol level, potentially enabling advanced persistent threats to undermine the fundamental security properties of the Tor network. The impact extends beyond individual user privacy to affect the entire network's integrity and security model.
The mitigation strategy for CVE-2012-3519 involves implementing constant-time execution patterns in the relay list iteration process. The most effective solution requires updating to Tor version 0.2.2.38 or later, which includes fixes specifically designed to eliminate the timing variations in relay selection operations. Organizations and users should prioritize immediate deployment of patched Tor versions to prevent exploitation of this vulnerability. Security practitioners should also implement monitoring for timing anomalies in network traffic analysis, as part of broader defensive measures against side-channel attacks. The fix addresses the underlying implementation issue by ensuring that relay iteration operations maintain consistent execution time regardless of the specific relay being processed, thereby eliminating the information leakage channel that attackers could exploit. This remediation aligns with ATT&CK technique T1059.001 for timing-based reconnaissance and addresses the broader category of side-channel attack prevention.