CVE-2016-10207 in TigerVNC
Summary
by MITRE
The Xvnc server in TigerVNC allows remote attackers to cause a denial of service (invalid memory access and crash) by terminating a TLS handshake early.
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Analysis
by VulDB Data Team • 09/02/2020
The vulnerability identified as CVE-2016-10207 resides within the Xvnc server component of TigerVNC software, representing a significant security weakness that enables remote attackers to execute denial of service attacks through carefully crafted TLS handshake termination. This flaw specifically targets the server's handling of secure communication protocols, where improper validation of TLS connection states leads to memory access violations and subsequent system crashes. The issue manifests when an attacker prematurely terminates a TLS handshake process, causing the Xvnc server to encounter invalid memory references that result in application instability and complete service disruption.
From a technical perspective, this vulnerability operates at the protocol handling layer of the VNC server implementation, where the software fails to properly validate the state of TLS connections during the negotiation phase. The flaw constitutes a classic buffer overflow or memory corruption issue that occurs when the server attempts to process incomplete TLS handshake data structures. According to CWE classification, this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and CWE-248, which covers exposure of an exception to the calling environment. The improper handling of TLS handshake termination creates an execution path where the server's memory management routines encounter corrupted or uninitialized data structures, leading to invalid memory access patterns that crash the application.
The operational impact of this vulnerability extends beyond simple service disruption, as it provides attackers with a reliable method to compromise the availability of VNC services across networked environments. Organizations relying on TigerVNC for remote desktop access face significant risks when this vulnerability remains unpatched, as attackers can repeatedly exploit the flaw to maintain persistent service degradation. The vulnerability is particularly concerning in enterprise environments where VNC servers serve as critical remote access points for system administrators and support personnel. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network denial of service attacks, and T1566.001, covering spearphishing through social engineering, as attackers may use this vulnerability to target specific systems for availability disruption.
Mitigation strategies for CVE-2016-10207 require immediate implementation of software updates from TigerVNC vendors, as the fix typically involves enhanced TLS handshake validation and proper memory state management within the server's protocol handling components. Network administrators should also implement monitoring solutions to detect abnormal TLS handshake termination patterns that may indicate exploitation attempts. Additionally, organizations should consider implementing network segmentation to limit exposure of VNC servers to untrusted networks, while ensuring that all VNC implementations undergo regular security assessments. The vulnerability highlights the importance of robust input validation in cryptographic protocol implementations and underscores the need for comprehensive security testing of network services that handle TLS connections.