CVE-2011-1924 in Tor
Summary
by MITRE
Buffer overflow in the policy_summarize function in or/policies.c in Tor before 0.2.1.30 allows remote attackers to cause a denial of service (directory authority crash) via a crafted policy that triggers creation of a long port list.
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Analysis
by VulDB Data Team • 11/08/2021
The vulnerability identified as CVE-2011-1924 represents a critical buffer overflow flaw within the Tor anonymization network software ecosystem. This issue specifically affects the policy_summarize function located in the or/policies.c source file, which is part of the Tor directory authority implementation. The vulnerability manifests when the software processes crafted policy information that contains an excessively long port list, leading to improper memory handling and subsequent system instability. The flaw exists in Tor versions prior to 0.2.1.30, making a significant portion of the network susceptible to exploitation by malicious actors seeking to disrupt the directory authority services that maintain the network's routing infrastructure.
The technical execution of this vulnerability relies on the manipulation of policy data structures within Tor's directory authority system. When a malicious actor crafts a policy document containing an abnormally extended port list, the policy_summarize function fails to properly validate the length of the input data before attempting to process it. This failure results in a buffer overflow condition where data written beyond the allocated memory boundaries corrupts adjacent memory regions. The overflow occurs during the creation of the port list structure, which is a fundamental component of Tor's policy enforcement mechanisms. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, where insufficient bounds checking allows attackers to overwrite critical memory locations and potentially execute arbitrary code or cause system crashes.
The operational impact of this vulnerability extends beyond simple denial of service, as it specifically targets the directory authority nodes that serve as critical infrastructure for the Tor network's proper functioning. When exploited, the vulnerability causes directory authority crashes that can fragment the network and compromise the anonymity services that depend on these authoritative nodes for routing information. The disruption affects not only the targeted authority but can also cascade through the network as other nodes attempt to rebuild their routing tables and redistribute the lost information. This type of attack aligns with ATT&CK technique T1499.004, which involves network disruption attacks targeting infrastructure components to degrade service availability. The vulnerability's potential for causing widespread network instability makes it particularly dangerous in the context of a privacy-focused infrastructure like Tor, where maintaining network integrity is paramount to user security.
Mitigation strategies for CVE-2011-1924 require immediate patching of affected Tor installations to version 0.2.1.30 or later, which contains the necessary memory validation fixes. Network administrators should implement strict input validation policies for all policy-related data processing within their Tor deployments, including monitoring for unusual port list lengths and implementing rate limiting for policy updates. The fix implemented in the patched versions involves enhanced bounds checking within the policy_summarize function to prevent buffer overflow conditions when processing port lists. Additional defensive measures include deploying intrusion detection systems that monitor for anomalous policy data patterns and implementing network segmentation to isolate directory authority nodes from potentially malicious traffic sources. Organizations should also consider maintaining multiple directory authority instances to reduce single points of failure and ensure continued network operation even if individual nodes are compromised. The vulnerability highlights the importance of robust memory management practices in network security infrastructure and demonstrates the critical need for thorough input validation in security-sensitive applications.