CVE-2015-2928 in Tor
Summary
by MITRE
The Hidden Service (HS) server implementation in Tor before 0.2.4.27, 0.2.5.x before 0.2.5.12, and 0.2.6.x before 0.2.6.7 allows remote attackers to cause a denial of service (assertion failure and daemon exit) via unspecified vectors.
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Analysis
by VulDB Data Team • 05/03/2022
The vulnerability identified as CVE-2015-2928 represents a critical denial of service weakness within the Tor network's Hidden Service server implementation across multiple versions of the software. This flaw specifically affects Tor versions prior to 0.2.4.27, 0.2.5.12, and 0.2.6.7, creating a significant risk for users relying on Tor's anonymity services. The vulnerability manifests through unspecified vectors that can trigger assertion failures within the Tor daemon, ultimately leading to complete daemon termination and service disruption for hidden service users.
The technical nature of this vulnerability stems from inadequate input validation and error handling within the hidden service server component of Tor. When remote attackers exploit this weakness, they can craft malicious inputs or requests that cause the Tor daemon to encounter assertion failures, which are typically used to catch programming errors during development. These assertion failures are not properly handled in production code, resulting in the daemon exiting unexpectedly and terminating all hidden service operations. The flaw operates at the core level of Tor's service implementation, making it particularly dangerous as it can affect the availability of anonymity services that thousands of users depend upon.
From an operational perspective, this vulnerability creates substantial risk for both individual users and organizations utilizing Tor for legitimate anonymity purposes. The denial of service condition can be exploited by malicious actors to disrupt access to hidden services, potentially compromising the operational integrity of websites and services hosted within the Tor network. This weakness directly impacts the reliability of Tor's anonymity infrastructure and can be leveraged to undermine the network's availability, which is fundamental to its security model. The impact extends beyond simple service disruption as it can affect the trust users place in the Tor network's stability and reliability for sensitive communications.
The vulnerability aligns with CWE-617, which addresses reachable assertions, and represents a classic example of how improper error handling can lead to denial of service conditions. From an ATT&CK framework perspective, this weakness maps to T1499.004, which covers network denial of service attacks, and demonstrates how attackers can exploit software implementation flaws to compromise system availability. Organizations and users should immediately upgrade to patched versions of Tor to mitigate this risk, as the vulnerability can be exploited remotely without requiring authentication or special privileges. The patching process should be prioritized given the potential for widespread disruption of hidden service operations and the critical nature of maintaining anonymity services within the Tor network ecosystem.