CVE-2012-3517 in Tor
Summary
by MITRE
Use-after-free vulnerability in dns.c in Tor before 0.2.2.38 might allow remote attackers to cause a denial of service (daemon crash) via vectors related to failed DNS requests.
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Analysis
by VulDB Data Team • 04/12/2021
The vulnerability identified as CVE-2012-3517 represents a critical use-after-free flaw within the Tor anonymization network's DNS handling component. This issue exists in the dns.c file of Tor versions prior to 0.2.2.38, creating a scenario where remote attackers can exploit the daemon's response to failed DNS requests to trigger a denial of service condition. The vulnerability stems from improper memory management practices that allow freed memory locations to be accessed after the memory has been deallocated, a classic pattern that can lead to unpredictable behavior and system instability.
The technical implementation of this vulnerability involves the Tor daemon's handling of DNS resolution failures within its network routing infrastructure. When DNS requests fail, the Tor client processes these failures in a manner that does not properly account for memory deallocation sequences. This creates a window where memory that has been freed by the application's internal DNS processing routines can still be referenced or accessed by subsequent operations, leading to memory corruption. The use-after-free condition manifests as a crash of the Tor daemon process, effectively terminating the anonymization service and rendering the network connection unstable.
From an operational perspective, this vulnerability poses significant risks to the Tor network's reliability and availability. The denial of service impact means that remote attackers can disrupt the anonymity services provided by Tor nodes, potentially compromising the network's integrity and user privacy. The vulnerability's remote exploitability allows adversaries to target Tor daemon processes without requiring local access, making it particularly dangerous for network infrastructure. This weakness can be leveraged to create cascading failures within the Tor network, where multiple nodes may crash simultaneously, leading to broader service disruption.
The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software applications. This classification indicates that the flaw involves accessing memory after it has been freed, a common pattern in memory safety violations. The ATT&CK framework categorizes this as a denial of service attack vector through memory corruption, potentially enabling adversaries to disrupt network services and compromise system availability. The impact extends beyond simple daemon crashes to potentially affecting the entire Tor network's routing capabilities and user anonymity guarantees.
Mitigation strategies for CVE-2012-3517 require immediate deployment of Tor version 0.2.2.38 or later, which contains the necessary memory management fixes. Organizations should implement comprehensive patch management protocols to ensure all Tor instances are updated promptly. Network administrators should monitor for signs of exploitation attempts and consider implementing additional network-level protections such as rate limiting for DNS requests. The fix addresses the underlying memory management issues by ensuring proper synchronization of memory allocation and deallocation sequences within the DNS processing code, preventing the access of freed memory locations during error handling scenarios.