CVE-2011-0015 in Tor
Summary
by MITRE
Tor before 0.2.1.29 and 0.2.2.x before 0.2.2.21-alpha does not properly check the amount of compression in zlib-compressed data, which allows remote attackers to cause a denial of service via a large compression factor.
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Analysis
by VulDB Data Team • 08/02/2024
The vulnerability identified as CVE-2011-0015 affects the Tor anonymity network software, specifically versions prior to 0.2.1.29 and 0.2.2.x versions before 0.2.2.21-alpha. This flaw resides in the handling of zlib-compressed data within the Tor protocol implementation, representing a critical security weakness that impacts the network's reliability and availability. The issue stems from insufficient validation of compression parameters during data processing, creating a potential vector for malicious actors to disrupt network operations.
The technical implementation flaw occurs within the decompression logic where Tor fails to properly validate the compression ratio of incoming zlib-compressed data streams. When processing compressed data, the software does not adequately check whether the compression factor exceeds reasonable thresholds, allowing attackers to craft specially formatted compressed data that triggers excessive decompression operations. This weakness falls under the category of improper input validation as defined by CWE-20, specifically involving the failure to validate compression parameters in data processing pipelines. The vulnerability manifests when an attacker sends compressed data with an extremely high compression ratio, causing the decompression process to consume excessive computational resources and memory.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can severely compromise the stability and performance of Tor network nodes. Remote attackers can exploit this weakness to consume disproportionate system resources, potentially leading to system crashes, memory exhaustion, or complete service unavailability for legitimate users. The attack vector is particularly concerning because it can be executed remotely without requiring authentication or specialized privileges, making it accessible to anyone capable of establishing connections to Tor network endpoints. This vulnerability directly maps to the ATT&CK technique T1499.004, which describes denial of service through resource exhaustion attacks.
Mitigation strategies for CVE-2011-0015 involve immediate software updates to patched versions of Tor, specifically versions 0.2.1.29 and 0.2.2.21-alpha or later. Network administrators should also implement additional monitoring and rate-limiting mechanisms to detect unusual compression patterns in incoming data streams. The fix implemented in the patched versions includes enhanced validation of compression ratios during decompression processes, ensuring that compressed data meets acceptable size thresholds before processing. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates across all Tor installations. The vulnerability demonstrates the importance of proper resource management in network protocols and highlights the need for robust input validation in cryptographic and anonymization systems to prevent resource exhaustion attacks that could undermine the fundamental security properties these systems are designed to provide.