CVE-2022-24750 is a vulnerability identified in UltraVNC, an open-source remote PC access software widely used for remote desktop control and support. The flaw exists in versions prior to 1.3.8.0 and specifically affects the DSM (Data Stream Modification) plugin module. This module is responsible for handling encryption and authentication plugins within UltraVNC. The vulnerability is classified under CWE-269, indicating improper privilege management. An authenticated local user can exploit this flaw to escalate their privileges on the affected system, gaining higher-level access than intended. The root cause lies in the plugin loading mechanism, which previously allowed plugins to be loaded from arbitrary locations rather than restricting them to the installed directory. This improper restriction enables a local attacker to load a malicious plugin, thereby executing code with elevated privileges. The issue has been addressed in UltraVNC version 1.3.8.1 by enforcing plugin loading only from the installed directory, mitigating the risk of unauthorized privilege escalation. For users unable to upgrade, it is recommended not to run the UltraVNC server as a Windows service, as this mode is vulnerable. Instead, launching WinVNC.exe via a scheduled task under a low-privilege account is advised. No effective workaround exists if the server must run as a service. There are no known exploits in the wild at this time, but the vulnerability poses a significant risk in environments where local user accounts are not tightly controlled or where UltraVNC is deployed on critical systems.

The primary impact of this vulnerability is local privilege escalation, which can compromise the confidentiality, integrity, and availability of affected systems. An attacker with local authenticated access—such as a standard user or a compromised account—can leverage this flaw to gain administrative or SYSTEM-level privileges. This elevation enables the attacker to install malware, modify system configurations, disable security controls, or move laterally within the network. For European organizations, particularly those in sectors relying heavily on remote desktop tools for IT support, this vulnerability could facilitate insider threats or post-compromise escalation. The risk is heightened in environments where UltraVNC is deployed on servers or workstations with sensitive data or critical infrastructure. Additionally, organizations that run UltraVNC as a service without proper restrictions are at greater risk. The lack of known exploits in the wild reduces immediate threat but does not eliminate the potential for targeted attacks, especially given the availability of the vulnerability details. The impact on availability could also be significant if an attacker disrupts remote access capabilities or uses elevated privileges to disable security monitoring.

To mitigate this vulnerability, European organizations should prioritize upgrading UltraVNC to version 1.3.8.1 or later, where the plugin loading path is properly restricted. For environments where immediate upgrade is not feasible, it is critical to avoid running the UltraVNC server as a Windows service, as this mode is vulnerable to privilege escalation. Instead, configure UltraVNC to launch via a scheduled task under a low-privilege user account to reduce the attack surface. Organizations should audit existing UltraVNC deployments to identify versions in use and verify service configurations. Implement strict local user account management and limit the number of users with local authenticated access to systems running UltraVNC. Employ application whitelisting and endpoint detection to monitor for unauthorized plugin loading or suspicious process behavior. Additionally, network segmentation and restricting remote access to UltraVNC servers can reduce exposure. Regularly review logs for unusual privilege escalation attempts and maintain up-to-date backups to recover from potential compromises. Finally, consider alternative remote access solutions with stronger security postures if UltraVNC cannot be securely configured.