CVE-2019-8272 in UltraVNC
Summary
by MITRE
UltraVNC revision 1211 has multiple off-by-one vulnerabilities in VNC server code, which can potentially result in code execution. This attack appears to be exploitable via network connectivity. These vulnerabilities have been fixed in revision 1212.
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Analysis
by VulDB Data Team • 05/28/2020
The vulnerability identified as CVE-2019-8272 affects UltraVNC server software at revision 1211, representing a critical security flaw that has been addressed in revision 1212. This issue manifests as multiple off-by-one vulnerabilities within the VNC server codebase, which are particularly dangerous due to their potential for remote code execution. The vulnerabilities arise from improper bounds checking in memory allocation and buffer handling operations that are fundamental to the VNC protocol implementation.
These off-by-one errors occur when the VNC server fails to properly validate input boundaries during memory operations, creating opportunities for attackers to manipulate memory layout and potentially execute arbitrary code. The vulnerabilities are classified under CWE-129, which specifically addresses insufficient validation of length of inputs, and are particularly concerning because they exist in the core server functionality that handles network communications from remote clients. The attack vector requires only network connectivity, making these vulnerabilities highly exploitable in environments where VNC servers are exposed to untrusted networks.
The operational impact of CVE-2019-8272 extends beyond simple privilege escalation or denial of service scenarios. Attackers who successfully exploit these vulnerabilities can gain full control over affected systems, potentially leading to data breaches, system compromise, and lateral movement within network environments. The nature of VNC servers as remote desktop solutions means that successful exploitation can provide attackers with complete access to target systems, including the ability to monitor user sessions, execute commands, and exfiltrate sensitive information. This vulnerability aligns with ATT&CK technique T1071.005 for application layer protocol usage and T1059 for command and scripting interpreter usage.
Organizations using UltraVNC revision 1211 should immediately implement mitigations including patching to revision 1212, network segmentation to limit exposure, and monitoring for suspicious network traffic patterns. The vulnerability demonstrates the critical importance of proper input validation in network services, particularly those handling remote user connections. Security teams should also consider implementing additional network controls such as firewall rules restricting VNC server access to trusted IP ranges and monitoring for unusual connection patterns that might indicate exploitation attempts. The fix in revision 1212 addresses the underlying memory handling issues through improved bounds checking and input validation mechanisms that prevent the off-by-one conditions from being exploited.