CVE-2025-66266 is a critical vulnerability classified under CWE-269 (Improper Privilege Management) affecting MegaTec Taiwan's UPSilon2000V6.0, specifically version 6.0.5. The vulnerability arises from insecure permissions on the RupsMon.exe service executable, which is part of the UPSilon2000 software suite used for uninterruptible power supply (UPS) management. The executable's permissions are set to allow the 'Everyone' group Full Control, meaning any local user can modify or replace the executable. An attacker with local access can exploit this by substituting the legitimate RupsMon.exe with a malicious binary or by changing the service's configuration path to point to a malicious command. Upon starting or stopping the service, the malicious code executes with SYSTEM-level privileges, resulting in immediate privilege escalation without requiring authentication or user interaction. The vulnerability has a CVSS 4.0 base score of 9.3, indicating critical severity, with attack vector local, low attack complexity, no privileges required, and no user interaction needed. The impact covers confidentiality, integrity, and availability, as SYSTEM-level code execution can lead to full system compromise. No patches or exploit code are currently publicly available, and no known exploits in the wild have been reported. However, the vulnerability's nature and ease of exploitation make it a significant threat to affected systems. The vulnerability was published on November 26, 2025, and assigned by Gridware. The lack of patch links suggests that remediation may require vendor coordination or manual permission adjustments. This vulnerability is particularly concerning for environments where UPSilon2000 is deployed to manage critical power infrastructure, as compromise could disrupt power management and cause cascading failures.

For European organizations, the impact of CVE-2025-66266 is substantial. UPSilon2000 is used to manage UPS devices that ensure continuous power supply to critical infrastructure such as data centers, hospitals, manufacturing plants, and telecommunications. Exploitation of this vulnerability allows a local attacker to gain SYSTEM privileges, potentially leading to full system compromise, unauthorized access to sensitive data, disruption of UPS management, and denial of power continuity. This can result in operational downtime, data loss, and safety risks, especially in sectors reliant on uninterrupted power. The vulnerability's local attack vector means that attackers need some level of access, which could be gained through insider threats, compromised endpoints, or lateral movement after initial breach. Given the criticality of power management systems, successful exploitation could have cascading effects on business continuity and safety compliance. European organizations with stringent regulatory requirements for critical infrastructure protection (e.g., NIS Directive, GDPR) may face compliance violations and reputational damage if exploited. The absence of known exploits provides a window for proactive mitigation, but the critical severity demands immediate action to prevent potential attacks.

To mitigate CVE-2025-66266, European organizations should take the following specific steps: 1) Immediately audit and restrict NTFS permissions on the RupsMon.exe executable and related service configuration files to remove 'Everyone' Full Control, limiting access to only trusted administrators and service accounts. 2) Implement application whitelisting to prevent unauthorized binaries from executing in the UPSilon2000 environment. 3) Monitor file integrity of the RupsMon.exe and service configuration paths using host-based intrusion detection systems (HIDS) to detect unauthorized changes. 4) Enforce strict local user account management and limit local administrative privileges to reduce the risk of local exploitation. 5) Segment networks to restrict access to UPSilon2000 management consoles and servers, minimizing exposure to potentially compromised endpoints. 6) Engage with MegaTec Taiwan for official patches or updates addressing this vulnerability and apply them promptly once available. 7) Conduct regular security awareness training to mitigate insider threats and ensure that local access is controlled and monitored. 8) Review and enhance logging and alerting on service start/stop events related to UPSilon2000 to detect suspicious activity. These targeted actions go beyond generic advice by focusing on permission hardening, monitoring, and access control specific to the vulnerable component.