CVE-2008-3493 in RealVNC Windows Client
Summary
by MITRE
vncviewer.exe in RealVNC Windows Client 4.1.2.0 allows remote VNC servers to cause a denial of service (application crash) via a crafted frame buffer update packet.
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Analysis
by VulDB Data Team • 11/02/2024
The vulnerability identified as CVE-2008-3493 affects the RealVNC Windows Client version 4.1.2.0 where the vncviewer.exe application fails to properly validate incoming frame buffer update packets from remote VNC servers. This flaw represents a classic buffer overflow condition that occurs during the processing of malformed network data, specifically within the frame buffer update handling mechanism of the VNC client software. The issue arises when the client receives a specially crafted packet that exceeds expected buffer boundaries, leading to memory corruption and subsequent application instability.
From a technical perspective, this vulnerability operates as a remote denial of service attack vector that does not require authentication or privileged access to exploit. The flaw stems from inadequate input validation within the VNC protocol implementation, where the client application does not properly sanitize or bounds-check the data received during frame buffer updates. This weakness allows a malicious remote VNC server to send malformed packets that trigger memory corruption, causing the vncviewer.exe process to crash and terminate unexpectedly. The vulnerability maps to CWE-121, which describes stack-based buffer overflow conditions, and also aligns with CWE-125, representing out-of-bounds read conditions that can occur when processing malformed input data.
The operational impact of this vulnerability extends beyond simple service disruption as it can be leveraged to create persistent availability issues for VNC clients in enterprise environments. Organizations relying on VNC for remote desktop management, technical support, or system administration may experience unexpected client failures during critical operations, potentially leading to service interruptions and increased administrative overhead. Attackers could exploit this weakness to repeatedly crash VNC sessions, creating a denial of service condition that prevents legitimate users from accessing systems through the VNC interface. This vulnerability particularly affects environments where VNC clients are used for remote support or system administration, as it can be triggered without requiring any user interaction beyond establishing a VNC connection to a malicious server.
Mitigation strategies for CVE-2008-3493 should focus on immediate patching of the RealVNC client software to version 4.1.3.0 or later, which contains the necessary fixes for the buffer handling issues. Network segmentation and access controls should be implemented to limit exposure of VNC clients to untrusted networks, as this vulnerability is most effectively exploited when attackers can establish direct connections to vulnerable clients. Additionally, implementing network monitoring to detect anomalous VNC traffic patterns and establishing robust incident response procedures for handling VNC-related service disruptions will help minimize the operational impact. Organizations should also consider implementing alternative remote access solutions with more robust security implementations, as VNC has historically shown vulnerabilities related to authentication bypasses and protocol-level weaknesses. The ATT&CK framework categorizes this vulnerability under T1499.004 for network denial of service attacks and T1566.001 for credential harvesting through remote services, highlighting the multi-faceted nature of the threat landscape surrounding VNC implementations.