CVE-2009-2425 in Tor
Summary
by MITRE
Tor before 0.2.0.35 allows remote attackers to cause a denial of service (application crash) via a malformed router descriptor.
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Analysis
by VulDB Data Team • 11/18/2018
The vulnerability identified as CVE-2009-2425 represents a critical denial of service flaw in the Tor anonymity network affecting versions prior to 0.2.0.35. This vulnerability specifically targets the router descriptor processing functionality within Tor's directory system, which serves as the foundation for maintaining network topology information and routing decisions. The flaw arises from insufficient input validation when processing router descriptors, which are essential components that describe network nodes and their capabilities within the Tor network.
The technical implementation of this vulnerability exploits a buffer overflow condition that occurs when Tor processes malformed router descriptors containing specially crafted data structures. When a malicious actor crafts a router descriptor with irregular or oversized fields, the parsing routine fails to properly handle the malformed input, leading to memory corruption and subsequent application crash. This vulnerability operates at the protocol level within Tor's directory subsystem, where router descriptors are exchanged between directory authorities and relay nodes to maintain network integrity and routing information.
From an operational perspective, this vulnerability presents a significant risk to the Tor network's stability and availability. Attackers can remotely trigger service disruption by sending malicious router descriptors to any Tor node, potentially causing cascading failures across the network. The impact extends beyond individual node crashes to potentially destabilizing entire network segments, as directory authorities rely heavily on proper router descriptor processing for maintaining network topology. This vulnerability directly impacts the network's ability to route traffic securely and efficiently, undermining the fundamental anonymity services that Tor provides to users.
The flaw aligns with CWE-121, which categorizes buffer overflow conditions as critical security weaknesses, and demonstrates how improper input validation can lead to application instability. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, representing network disruption through service availability attacks, and T1566.002, involving social engineering through spearphishing with attachments. The vulnerability exploits the trust model inherent in Tor's directory system where nodes accept and process information from other network participants without sufficient validation. Mitigation strategies include upgrading to Tor version 0.2.0.35 or later, implementing network-level filtering of malformed descriptors, and deploying intrusion detection systems to monitor for suspicious descriptor patterns. Organizations should also consider implementing redundant directory services and maintaining proper network segmentation to limit the impact of potential exploitation attempts.