CVE-2014-6051 in LibVNCServer
Summary
by MITRE
Integer overflow in the MallocFrameBuffer function in vncviewer.c in LibVNCServer 0.9.9 and earlier allows remote VNC servers to cause a denial of service (crash) and possibly execute arbitrary code via an advertisement for a large screen size, which triggers a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 03/29/2022
The vulnerability identified as CVE-2014-6051 represents a critical integer overflow flaw within the LibVNCServer library version 0.9.9 and earlier, specifically within the MallocFrameBuffer function located in vncviewer.c. This issue arises from inadequate input validation when processing screen size advertisements from remote VNC servers, creating a pathway for malicious actors to manipulate memory allocation parameters. The flaw manifests when a remote VNC server presents an advertisement for an excessively large screen dimension that, upon processing, causes integer overflow during heap allocation calculations. This vulnerability falls under the CWE-190 category of Integer Overflow or Wraparound, which is a well-documented weakness in software systems where arithmetic operations exceed the maximum representable value for the data type involved.
The technical exploitation of this vulnerability occurs through a carefully crafted screen size advertisement that, when processed by the vulnerable LibVNCServer component, triggers an integer overflow condition. The MallocFrameBuffer function fails to properly validate the screen dimensions provided by the remote server, allowing an attacker to specify dimensions that, when converted to heap allocation parameters, result in insufficient memory allocation. This insufficient allocation creates a heap-based buffer overflow condition where subsequent memory operations can overwrite adjacent memory regions. The attack vector is particularly dangerous because it requires no authentication or privileged access, making it a remote code execution vulnerability that can be exploited over network connections. According to ATT&CK framework, this represents a privilege escalation technique through memory corruption, specifically targeting the application layer of the network stack.
The operational impact of CVE-2014-6051 extends beyond simple denial of service scenarios to potentially enable arbitrary code execution on affected systems. When exploited successfully, the heap-based buffer overflow can allow remote attackers to inject and execute malicious code within the context of the vulnerable VNC client application. This vulnerability affects any system running LibVNCServer 0.9.9 or earlier versions, including desktop VNC clients and server implementations that utilize this library. The crash conditions can be reliably reproduced by sending a specially crafted screen size advertisement, making this vulnerability particularly attractive to attackers seeking to disrupt services or establish persistent access to target systems. Organizations utilizing VNC protocols for remote desktop access face significant risk from this vulnerability, as it can be exploited by attackers who gain access to the network segment where VNC services operate.
Mitigation strategies for CVE-2014-6051 primarily focus on immediate software updates and patches to LibVNCServer to versions that address the integer overflow condition in the MallocFrameBuffer function. System administrators should prioritize patching all affected VNC clients and servers, as the vulnerability affects both client and server implementations that utilize the vulnerable library. Additional protective measures include implementing network segmentation to limit exposure of VNC services to untrusted networks, configuring firewall rules to restrict VNC access to authorized IP addresses, and monitoring for suspicious screen size advertisements in network traffic. Organizations should also consider implementing intrusion detection systems that can identify anomalous VNC protocol behavior patterns. The vulnerability demonstrates the importance of proper integer overflow protection in memory management functions, particularly in network-facing applications, and highlights the necessity of thorough input validation in security-critical code sections. Regular security assessments and code reviews focusing on memory allocation routines can help identify similar vulnerabilities before they can be exploited by malicious actors.