CVE-2026-20820 is a heap-based buffer overflow vulnerability identified in the Windows Common Log File System Driver component of Microsoft Windows Server 2022, specifically version 10.0.20348.0. This vulnerability is classified under CWE-122, indicating improper handling of memory buffers leading to overflow conditions. The flaw allows an attacker with authorized local access to the system to execute a privilege escalation attack, thereby gaining elevated system privileges. The vulnerability does not require user interaction and has a low attack complexity, meaning it can be exploited reliably by an attacker who already has some level of access to the system. Exploiting this vulnerability could lead to full compromise of the affected server, impacting confidentiality, integrity, and availability of data and services. Although no known exploits are currently reported in the wild, the presence of this vulnerability in a critical system component like the Common Log File System Driver makes it a significant risk. The CVSS v3.1 base score of 7.8 reflects the high impact on system security and the ease of exploitation given local access. The vulnerability was reserved in December 2025 and published in January 2026, with no patches currently available, emphasizing the need for vigilance and interim mitigations.

For European organizations, the impact of CVE-2026-20820 can be severe, particularly for enterprises and public sector entities relying on Windows Server 2022 for critical infrastructure, data centers, and enterprise applications. Successful exploitation can lead to unauthorized privilege escalation, allowing attackers to execute arbitrary code with system-level privileges, potentially leading to data breaches, service disruptions, and lateral movement within networks. This could compromise sensitive personal data protected under GDPR, resulting in regulatory penalties and reputational damage. The availability of critical services hosted on affected servers could be disrupted, impacting business continuity. Given the local access requirement, insider threats or attackers who have already gained foothold via other means could leverage this vulnerability to deepen their control. The absence of known exploits currently provides a window for proactive defense, but the high severity score necessitates urgent attention to prevent future exploitation.

1. Apply official security patches from Microsoft immediately once they become available to remediate the vulnerability in the Common Log File System Driver. 2. Until patches are released, restrict local administrative access to Windows Server 2022 systems to trusted personnel only, minimizing the risk of exploitation by unauthorized users. 3. Implement strict access controls and monitoring on servers to detect unusual privilege escalation attempts or anomalous behavior related to the Common Log File System Driver. 4. Employ endpoint detection and response (EDR) solutions capable of identifying exploitation attempts targeting heap-based buffer overflows or privilege escalation techniques. 5. Conduct regular security audits and vulnerability assessments focusing on Windows Server environments to identify and remediate potential attack vectors. 6. Harden server configurations by disabling unnecessary services and features that could provide local access vectors. 7. Educate system administrators and security teams about this vulnerability and the importance of rapid patch management and incident response readiness.