CVE-2025-26677 is a high-severity vulnerability classified under CWE-400 (Uncontrolled Resource Consumption) affecting Microsoft Windows Server 2019, specifically version 10.0.17763.0. The vulnerability resides in the Remote Desktop Gateway Service, which is responsible for securely tunneling Remote Desktop Protocol (RDP) sessions over HTTPS. An unauthorized attacker can exploit this flaw remotely without any authentication or user interaction by sending specially crafted requests to the Remote Desktop Gateway Service. This triggers excessive resource consumption on the affected server, leading to denial of service (DoS) conditions. The vulnerability does not impact confidentiality or integrity but severely affects availability by exhausting critical system resources such as memory, CPU, or network sockets. The CVSS 3.1 base score of 7.5 reflects the network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), and no user interaction (UI:N), with a scope unchanged (S:U) and impact limited to availability (A:H). No known exploits are currently reported in the wild, and no patches have been released yet. However, the presence of this vulnerability in a core Windows Server component that is often exposed to external networks makes it a significant risk for organizations relying on Remote Desktop Gateway for secure remote access.

For European organizations, the impact of CVE-2025-26677 can be substantial, especially for enterprises and public sector entities that depend on Windows Server 2019 Remote Desktop Gateway for remote workforce enablement, cloud services, and internal administrative access. Exploitation could lead to service outages, disrupting business continuity and critical operations. This is particularly concerning for sectors such as finance, healthcare, government, and telecommunications, where availability is crucial. The denial of service could also indirectly affect compliance with regulations like GDPR if service interruptions impact data processing or availability commitments. Additionally, the vulnerability could be leveraged as part of a multi-stage attack to distract or delay incident response teams while other malicious activities occur. Given the lack of authentication and user interaction requirements, attackers could scan and target exposed Remote Desktop Gateway endpoints en masse, increasing the risk of widespread disruption across European networks.

Immediate mitigation steps include restricting external access to Remote Desktop Gateway services through network-level controls such as firewalls and VPNs, limiting exposure to trusted IP ranges only. Organizations should implement strict network segmentation to isolate Remote Desktop Gateway servers from critical infrastructure. Monitoring network traffic for unusual spikes or patterns indicative of resource exhaustion attacks is essential. Administrators should also review and harden Remote Desktop Gateway configurations, disabling unnecessary features and enforcing rate limiting if supported. Since no patches are currently available, applying vendor advisories promptly once released is critical. Additionally, deploying Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with signatures or heuristics targeting anomalous Remote Desktop Gateway traffic can help block exploit attempts. Regularly updating Windows Server 2019 to the latest cumulative updates and security patches will reduce exposure to related vulnerabilities. Finally, organizations should prepare incident response plans specifically addressing denial of service scenarios targeting Remote Desktop services.