CVE-2012-3518 in Tor
Summary
by MITRE
The networkstatus_parse_vote_from_string function in routerparse.c in Tor before 0.2.2.38 does not properly handle an invalid flavor name, which allows remote attackers to cause a denial of service (out-of-bounds read and daemon crash) via a crafted (1) vote document or (2) consensus document.
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Analysis
by VulDB Data Team • 04/12/2021
The vulnerability identified as CVE-2012-3518 resides within the Tor anonymization network's router parsing functionality, specifically in the networkstatus_parse_vote_from_string function located in routerparse.c. This flaw represents a classic buffer over-read condition that occurs when the Tor daemon processes malformed vote or consensus documents. The vulnerability affects versions of Tor prior to 0.2.2.38, making it a significant concern for systems running outdated Tor software. The flaw stems from inadequate input validation within the parsing logic that fails to properly handle invalid flavor names, creating a path for remote attackers to exploit the daemon's memory handling mechanisms.
The technical implementation of this vulnerability demonstrates a clear violation of secure coding practices and can be classified under CWE-125: "Out-of-bounds Read" and CWE-476: "NULL Pointer Dereference". When the networkstatus_parse_vote_from_string function encounters a vote or consensus document containing an invalid flavor name, the parsing routine does not properly validate the input parameters before attempting to access memory locations. This improper handling leads to an out-of-bounds memory read operation that can cause the Tor daemon to crash or exhibit unpredictable behavior. The vulnerability operates at the protocol level where Tor's directory authorities exchange vote and consensus documents to maintain network topology information, making it particularly dangerous as it can disrupt the entire Tor network's operation.
The operational impact of CVE-2012-3518 extends beyond simple denial of service to potentially compromise the integrity of the Tor network's consensus mechanism. Remote attackers can craft malicious vote or consensus documents that trigger the out-of-bounds read condition, causing the targeted Tor daemon to crash and restart. This disruption can lead to temporary network instability, as the crashed daemon must be restarted and re-synchronize with the network. The attack vector is particularly concerning because it requires no authentication and can be executed against any Tor relay or directory authority that has not been updated to version 0.2.2.38 or later. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1499.004: "Endpoint Denial of Service" and can be leveraged to create network-level disruptions that affect the availability of anonymization services.
Mitigation strategies for CVE-2012-3518 primarily focus on immediate software updates to Tor version 0.2.2.38 or later, which contain the necessary patches to properly validate flavor names during document parsing. Network administrators should implement automated update mechanisms to ensure all Tor instances remain current with security patches. Additional defensive measures include implementing network monitoring to detect unusual daemon crash patterns and deploying intrusion detection systems that can identify crafted vote or consensus documents. The vulnerability also highlights the importance of proper input validation and bounds checking in network protocol implementations, emphasizing the need for robust error handling in cryptographic and anonymization software. Organizations relying on Tor infrastructure should conduct regular security assessments to identify and remediate similar vulnerabilities in their network services.