CVE-2011-4897 in Tor
Summary
by MITRE
Tor before 0.2.2.25-alpha, when configured as a relay without the Nickname configuration option, uses the local hostname as the Nickname value, which allows remote attackers to obtain potentially sensitive information by reading this value.
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Analysis
by VulDB Data Team • 02/13/2019
The vulnerability identified as CVE-2011-4897 affects the Tor anonymity network software version 0.2.2.25-alpha and earlier. This issue arises from improper configuration handling within the Tor relay implementation where the software automatically defaults to using the local hostname as the nickname value when no explicit nickname is configured by the administrator. The technical flaw stems from the software's failure to properly sanitize or validate the hostname information before publishing it within the Tor network's directory system, creating a situation where remote attackers can potentially extract sensitive information from the relay's configuration.
The operational impact of this vulnerability extends beyond simple information disclosure as it creates a vector for reconnaissance activities within the Tor network ecosystem. When a Tor relay operates without an explicitly defined nickname, the system automatically populates this field with the local hostname, which often contains identifying information about the underlying infrastructure, operating system, or organizational naming conventions. This information can be harvested by remote attackers through directory requests to the Tor network's directory servers, potentially revealing details about the relay's physical location, hosting environment, or administrative structure. The vulnerability particularly affects relay operators who may not be aware of this default behavior or who have not explicitly configured their systems for proper anonymity.
This vulnerability aligns with CWE-200, which addresses improper information exposure, and represents a specific implementation weakness in how the Tor software handles default configuration values. From an attack perspective, this issue maps to techniques described in the MITRE ATT&CK framework under reconnaissance activities where adversaries gather information about target systems before launching more sophisticated attacks. The exposure of hostname information can potentially enable attackers to correlate this data with other reconnaissance efforts, such as DNS enumeration or network scanning activities, thereby strengthening their understanding of the target infrastructure. The vulnerability also demonstrates poor security by design principles where default configurations do not adequately consider privacy implications in anonymity networks.
The recommended mitigation strategy involves explicitly configuring the Nickname option within the Tor relay configuration file, ensuring that relay operators consciously define unique identifiers that do not reveal system information. Administrators should also review their Tor configuration files to verify that no default behaviors are inadvertently exposing system information. Additionally, regular security audits of Tor network configurations should be conducted to ensure that all relay components are properly configured with appropriate anonymity protections. Network administrators should implement monitoring to detect any unauthorized changes to Tor configuration files and establish clear operational procedures for managing Tor relay deployments in sensitive environments. The vulnerability underscores the importance of explicit configuration over implicit defaults in privacy-critical systems and highlights the need for comprehensive security awareness training for operators of anonymity network infrastructure.