CVE-2019-8262 in UltraVNC
Summary
by MITRE
UltraVNC revision 1203 has multiple heap buffer overflow vulnerabilities in VNC client code inside Ultra decoder, which results in code execution. This attack appears to be exploitable via network connectivity. These vulnerabilities have been fixed in revision 1204.
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Analysis
by VulDB Data Team • 07/26/2023
The CVE-2019-8262 vulnerability represents a critical heap buffer overflow condition affecting UltraVNC client software at revision 1203, specifically within the Ultra decoder component of the VNC client codebase. This vulnerability falls under the Common Weakness Enumeration category CWE-121, which encompasses heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The flaw manifests in the client-side decoding logic responsible for processing remote desktop protocol data streams, creating a potential attack vector that could be exploited through network connectivity without requiring local system access.
The technical implementation of this vulnerability occurs when the UltraVNC client processes malformed data packets during remote desktop session establishment or data transmission. The buffer overflow vulnerability stems from inadequate input validation within the Ultra decoder module, which fails to properly verify the size of incoming data before attempting to copy it into fixed-size heap buffers. When an attacker crafts malicious data packets that exceed the allocated buffer boundaries, the excess data overflows into adjacent memory regions, potentially corrupting program execution flow, heap metadata, or other critical data structures. This memory corruption can lead to arbitrary code execution, allowing attackers to gain remote control over vulnerable systems.
The operational impact of CVE-2019-8262 extends beyond simple remote code execution, as it provides attackers with a means to establish persistent access to target systems within VNC environments. The vulnerability affects the core client-side functionality of UltraVNC, meaning that any system running the affected revision could be compromised when connecting to malicious VNC servers or when processing specially crafted VNC data streams. The attack surface is particularly concerning given that VNC protocols are commonly used for remote desktop management in enterprise environments, making this vulnerability potentially exploitable in corporate networks where VNC clients are prevalent. Security researchers have noted that the exploitability of this vulnerability is enhanced by the fact that it requires minimal user interaction beyond establishing a VNC connection, making it particularly dangerous in unattended systems or when users connect to untrusted VNC servers.
Mitigation strategies for CVE-2019-8262 primarily focus on immediate software updates to revision 1204, which contains the necessary patches to address the heap buffer overflow conditions. Organizations should implement comprehensive vulnerability management processes to identify all systems running affected UltraVNC revisions and prioritize their remediation. Network segmentation and access controls should be implemented to limit VNC client connectivity to trusted networks and systems, while also considering the deployment of network monitoring solutions that can detect anomalous VNC traffic patterns. The vulnerability demonstrates the importance of input validation and memory safety practices in remote desktop software, aligning with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1071.004 for Application Layer Protocol. Organizations should also consider implementing additional security controls such as mandatory access controls, network intrusion detection systems, and regular security assessments of remote desktop environments to prevent exploitation of similar vulnerabilities in other remote access software components.