CVE-2014-6052 in LibVNCServer
Summary
by MITRE
The HandleRFBServerMessage function in libvncclient/rfbproto.c in LibVNCServer 0.9.9 and earlier does not check certain malloc return values, which allows remote VNC servers to cause a denial of service (application crash) or possibly execute arbitrary code by specifying a large screen size in a (1) FramebufferUpdate, (2) ResizeFrameBuffer, or (3) PalmVNCReSizeFrameBuffer message.
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Analysis
by VulDB Data Team • 04/07/2022
The CVE-2014-6052 vulnerability resides within the LibVNCServer library, specifically in the HandleRFBServerMessage function located in libvncclient/rfbproto.c. This flaw represents a critical memory allocation oversight that affects versions 0.9.9 and earlier of the library. The vulnerability manifests when remote VNC servers send specially crafted messages containing excessive screen size parameters, creating a scenario where the application fails to properly validate memory allocation outcomes before proceeding with subsequent operations.
The technical exploitation of this vulnerability stems from the absence of proper malloc return value checking within the handling function. When a remote VNC server sends a FramebufferUpdate, ResizeFrameBuffer, or PalmVNCReSizeFrameBuffer message with an inflated screen dimension value, the application attempts to allocate memory based on this oversized parameter without verifying whether the allocation succeeded. This memory management failure creates a potential for both denial of service conditions and arbitrary code execution, as the application may attempt to write to invalid memory locations or trigger undefined behavior when processing the malformed data.
The operational impact of this vulnerability extends beyond simple service disruption, as it provides attackers with potential code execution capabilities within the context of the vulnerable application. The flaw aligns with CWE-704, which addresses improper handling of memory allocation failures, and demonstrates characteristics consistent with memory corruption vulnerabilities that can be leveraged for privilege escalation or system compromise. Attackers can exploit this weakness by establishing a connection to a vulnerable VNC server and sending maliciously crafted messages that force the application to attempt allocations of memory that exceed available resources or cause pointer corruption.
From an adversarial perspective, this vulnerability fits within the ATT&CK framework under the T1203 - Exploitation for Client Execution tactic, where adversaries leverage application vulnerabilities to execute malicious code. The vulnerability's remote exploitability means that attackers need only establish a network connection to the vulnerable VNC server to potentially gain control of the system. The lack of input validation in the screen size parameters creates a direct path for attackers to manipulate memory allocation behavior and potentially execute arbitrary code.
Mitigation strategies for CVE-2014-6052 should prioritize immediate patching of affected LibVNCServer installations to version 0.9.10 or later, where the memory allocation checks have been properly implemented. Organizations should also implement network segmentation and access controls to limit exposure to potentially malicious VNC connections, while monitoring for unusual screen size parameter values in VNC communications. Additionally, application-level input validation should be strengthened to include bounds checking for screen dimension parameters, ensuring that all memory allocations are verified before use. The vulnerability serves as a reminder of the critical importance of proper error handling in memory management operations and the potential consequences of overlooking fundamental security practices in network protocols.