CVE-2014-6054 in libvncserver
Summary
by MITRE
The rfbProcessClientNormalMessage function in libvncserver/rfbserver.c in LibVNCServer 0.9.9 and earlier allows remote attackers to cause a denial of service (divide-by-zero error and server crash) via a zero value in the scaling factor in a (1) PalmVNCSetScaleFactor or (2) SetScale message.
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Analysis
by VulDB Data Team • 03/29/2022
The vulnerability identified as CVE-2014-6054 resides within the LibVNCServer library version 0.9.9 and earlier, specifically in the rfbProcessClientNormalMessage function located in libvncserver/rfbserver.c. This flaw represents a critical security weakness that enables remote attackers to execute a denial of service attack against VNC servers implementing this library. The vulnerability manifests when the server receives specially crafted messages containing a zero value in the scaling factor parameter, which directly impacts the PalmVNCSetScaleFactor and SetScale message processing mechanisms. The issue stems from inadequate input validation and error handling within the server's message processing pipeline, creating a scenario where malformed scaling factor values can trigger unexpected system behavior.
The technical exploitation of this vulnerability occurs through the manipulation of VNC client-server communication protocols where attackers send maliciously crafted SetScale or PalmVNCSetScaleFactor messages containing zero as the scaling factor value. When the rfbProcessClientNormalMessage function processes these messages, it attempts to perform mathematical operations using the zero scaling factor without proper validation, resulting in a divide-by-zero error condition. This mathematical impossibility causes the server application to crash abruptly, terminating the VNC service and rendering the remote desktop functionality unavailable to legitimate users. The vulnerability demonstrates a classic lack of input sanitization and error handling practices that are fundamental to secure software development.
The operational impact of CVE-2014-6054 extends beyond simple service disruption to potentially compromise the availability of critical remote access infrastructure. Organizations relying on VNC servers for remote administration, technical support, or system maintenance operations face significant risk from this vulnerability, as attackers can systematically deny service to legitimate users without requiring authentication or specialized privileges. The attack vector is particularly concerning because it operates at the protocol level, making it difficult to distinguish between legitimate and malicious traffic. This vulnerability aligns with CWE-369, which addresses the issue of divide by zero errors in software implementations, and represents a clear violation of secure coding practices that should prevent such mathematical errors from causing system instability.
Mitigation strategies for CVE-2014-6054 require immediate attention from system administrators and security teams responsible for VNC server deployments. The most effective solution involves upgrading to LibVNCServer version 0.9.10 or later, where the vulnerability has been addressed through proper input validation and error handling mechanisms. Organizations should also implement network-level controls such as firewall rules that restrict VNC service access to trusted networks and employ monitoring solutions to detect unusual scaling factor values in VNC traffic. Additionally, administrators should consider implementing intrusion detection systems that can identify patterns consistent with this specific attack vector and deploy application-level firewalls that can filter out malformed VNC messages before they reach the vulnerable server components. The vulnerability also highlights the importance of following ATT&CK framework principles for defensive measures, particularly those related to privilege escalation and defense evasion techniques that attackers might employ to exploit such service-level vulnerabilities.