CVE-2016-8860 in Tor
Summary
by MITRE
Tor before 0.2.8.9 and 0.2.9.x before 0.2.9.4-alpha had internal functions that were entitled to expect that buf_t data had NUL termination, but the implementation of or/buffers.c did not ensure that NUL termination was present, which allows remote attackers to cause a denial of service (client, hidden service, relay, or authority crash) via crafted data.
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Analysis
by VulDB Data Team • 09/17/2024
The vulnerability identified as CVE-2016-8860 represents a critical buffer handling flaw within the Tor anonymity network software that affected versions prior to 0.2.8.9 and 0.2.9.4-alpha. This issue stems from a fundamental mismatch between the assumptions made by internal Tor functions and the actual implementation of buffer management. The affected components reside within the or/buffers.c file which serves as a core element for managing data buffers throughout the Tor network infrastructure. The flaw manifests when internal functions expect null-termination in buf_t data structures but the buffer implementation fails to guarantee this condition, creating a dangerous inconsistency that can be exploited by remote adversaries.
The technical nature of this vulnerability places it squarely within the realm of buffer overflow conditions and memory safety issues, specifically aligning with CWE-121 and CWE-125 categories that deal with improper handling of buffer boundaries and memory access violations. The implementation in or/buffers.c does not enforce null termination of buffer data, which creates a scenario where functions that rely on this assumption can encounter undefined behavior when processing crafted malicious input. This type of vulnerability is particularly dangerous in networked applications like Tor where data integrity is paramount for maintaining anonymity and security. The flaw can be exploited through carefully crafted data packets that, when processed by Tor clients, hidden services, relays, or authorities, trigger the buffer management inconsistency leading to application crashes.
The operational impact of CVE-2016-8860 extends across the entire Tor network ecosystem as it affects multiple node types including client software, hidden services, relay nodes, and authority servers. This vulnerability enables remote attackers to execute denial of service attacks that can selectively target specific Tor infrastructure components, potentially disrupting the anonymity network's functionality and reliability. The attack vector operates through network communication where malicious actors can send specially crafted data that causes the Tor software to crash upon processing the malformed buffers. This creates a significant risk for network availability and can be used to degrade service quality or even temporarily disable critical Tor infrastructure components.
Mitigation strategies for this vulnerability require immediate software updates to versions 0.2.8.9 or 0.2.9.4-alpha where the buffer management implementation has been corrected to ensure proper null termination. Network administrators should prioritize patching all Tor instances including client software, relay nodes, hidden services, and authority servers to prevent exploitation. Additionally, monitoring systems should be implemented to detect unusual crash patterns or network behavior that might indicate exploitation attempts. The fix addresses the root cause by modifying the or/buffers.c implementation to guarantee null termination of buf_t data structures before they are processed by functions that depend on this condition. This vulnerability demonstrates the importance of rigorous buffer management practices and proper input validation in security-critical software, particularly in anonymity networks where reliability and stability directly impact user privacy and security.
This vulnerability aligns with ATT&CK technique T1499.004 which covers "Network Denial of Service" and T1566.002 related to "Phishing with Malicious Attachments" as attackers could leverage this flaw to disrupt Tor services. The vulnerability also intersects with the broader category of software reliability issues that can be exploited to compromise availability, making it a significant concern for any organization relying on Tor infrastructure for secure communications or anonymity services.