CVE-2024-20691 is a medium-severity vulnerability identified in Microsoft Windows 10 Version 1809 (build 10.0.17763.0). It is classified as an out-of-bounds read vulnerability (CWE-125) related to Windows Themes, which can lead to information disclosure. Specifically, an out-of-bounds read occurs when the system reads data beyond the allocated memory buffer, potentially exposing sensitive information stored adjacent to the buffer. This vulnerability does not allow for code execution or system integrity compromise but can leak confidential data from memory. The CVSS v3.1 base score is 4.7, reflecting a medium severity level. The vector string indicates that the attack requires local access (AV:L), high attack complexity (AC:H), low privileges (PR:L), and no user interaction (UI:N). The scope is unchanged (S:U), and the impact affects confidentiality (C:H) but not integrity or availability (I:N, A:N). There are no known exploits in the wild at the time of publication, and no patches have been linked yet. The vulnerability was reserved on November 28, 2023, and published on January 9, 2024. It primarily affects legacy Windows 10 systems that are still running version 1809, which is an older release no longer supported by mainstream updates, increasing risk for unpatched environments. The vulnerability could be exploited by a local attacker with limited privileges to read sensitive information from memory related to Windows Themes, which might include user or system data that could aid further attacks or privacy breaches.

For European organizations, the impact of CVE-2024-20691 is primarily related to confidentiality breaches on legacy Windows 10 Version 1809 systems. Organizations that have not upgraded or patched these older systems may be vulnerable to local attackers gaining sensitive information, potentially including user credentials, configuration data, or other sensitive theme-related information. While the vulnerability does not allow for system compromise or denial of service, the information disclosure could facilitate subsequent attacks such as privilege escalation or lateral movement within networks. This is particularly concerning for sectors handling sensitive personal data under GDPR, where unauthorized disclosure could lead to regulatory penalties and reputational damage. The requirement for local access and high attack complexity limits remote exploitation, but insider threats or attackers with physical or remote desktop access could leverage this vulnerability. European organizations with legacy IT infrastructure, especially in critical sectors like government, healthcare, and finance, may face increased risk if these systems remain unpatched or unsupported.

To mitigate CVE-2024-20691, European organizations should prioritize upgrading affected systems from Windows 10 Version 1809 to a supported and fully patched Windows version, such as Windows 10 Version 22H2 or Windows 11. If immediate upgrade is not feasible, organizations should implement strict access controls to limit local user privileges and restrict physical and remote access to vulnerable systems. Employing endpoint detection and response (EDR) solutions to monitor for suspicious local activity can help detect exploitation attempts. Additionally, organizations should audit and harden theme-related configurations and remove unnecessary theme files or customizations that could be targeted. Regularly reviewing and enforcing least privilege principles for user accounts will reduce the attack surface. Finally, maintaining an inventory of legacy systems and applying any available security updates or workarounds from Microsoft as they are released is essential to reduce exposure.