CVE-2012-4922 in Tor
Summary
by MITRE
The tor_timegm function in common/util.c in Tor before 0.2.2.39, and 0.2.3.x before 0.2.3.22-rc, does not properly validate time values, which allows remote attackers to cause a denial of service (assertion failure and daemon exit) via a malformed directory object, a different vulnerability than CVE-2012-4419.
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Analysis
by VulDB Data Team • 04/13/2021
The CVE-2012-4922 vulnerability resides within the Tor anonymity network's time validation mechanism, specifically in the tor_timegm function located in common/util.c. This flaw represents a classic input validation weakness that can be exploited to disrupt the Tor daemon's operation through carefully crafted malformed directory objects. The vulnerability affects versions prior to 0.2.2.39 and 0.2.3.x versions before 0.2.3.22-rc, indicating it was present in multiple release branches of the Tor software. The issue stems from insufficient validation of time values during the processing of directory objects, which are essential components of the Tor network's directory structure that contain information about relay nodes and network topology.
The technical exploitation of this vulnerability occurs when remote attackers submit directory objects containing malformed time values that bypass proper validation checks within the tor_timegm function. This function is responsible for converting time values into a standardized format for network operations, but it fails to properly validate the range and format of input time values. When the function encounters invalid time data, it triggers an assertion failure that causes the Tor daemon to terminate abruptly, resulting in a denial of service condition that affects network connectivity for users relying on the compromised relay. The vulnerability is categorized under CWE-248 as an unspecified other flaw related to improper handling of time values, and it aligns with ATT&CK technique T1499.004 for network denial of service attacks targeting infrastructure components.
The operational impact of this vulnerability extends beyond simple daemon termination, as it can disrupt the entire Tor network's directory services and potentially affect the anonymity and accessibility of users within the network. When a relay node experiences this assertion failure, it removes itself from the network topology, reducing the available paths for traffic routing and potentially making it easier for adversaries to correlate traffic patterns. The vulnerability's classification as a denial of service issue means that attackers can systematically target relay nodes to degrade network performance or availability, which directly impacts the core functionality of the Tor network. This type of attack can be particularly damaging in the context of a distributed anonymity network where maintaining node availability is critical for user privacy and network stability.
Mitigation strategies for CVE-2012-4922 primarily involve upgrading to patched versions of the Tor software where proper time validation has been implemented in the tor_timegm function. Network administrators should ensure that all Tor relay nodes are updated to versions 0.2.2.39 or later, or 0.2.3.22-rc or later, depending on their current software branch. Additionally, implementing proper monitoring and alerting for assertion failures in Tor daemon logs can help detect exploitation attempts before they cause significant disruption. The vulnerability's remediation aligns with security best practices outlined in NIST SP 800-53 and ISO 27001 controls for input validation and system integrity, requiring that all time-related inputs be properly validated against expected ranges and formats to prevent unexpected program termination and maintain service availability.