CVE-2024-21377 is a numeric truncation error vulnerability (CWE-197) affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). This vulnerability specifically impacts the DNS component of the operating system, leading to an information disclosure flaw. Numeric truncation errors occur when a numeric value is improperly converted or truncated, potentially causing unexpected behavior or leakage of sensitive data. In this case, the flaw allows an attacker with limited privileges (local access with low privileges) to exploit the DNS subsystem to disclose sensitive information. The vulnerability does not require user interaction and does not affect system integrity or availability but has a high impact on confidentiality. The CVSS 3.1 base score is 5.5 (medium severity), with the vector indicating local attack vector (AV:L), low attack complexity (AC:L), requiring privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), high confidentiality impact (C:H), no integrity or availability impact (I:N/A:N). There are no known exploits in the wild as of the publication date, and no official patch links have been provided yet. The vulnerability was reserved in December 2023 and published in February 2024. It is important to note that this affects an older Windows 10 version (1809), which may still be in use in some enterprise environments but is no longer the latest supported version.

For European organizations, the primary impact of CVE-2024-21377 lies in the potential unauthorized disclosure of sensitive DNS-related information on affected Windows 10 Version 1809 systems. This could include internal network details, DNS queries, or cached DNS data that may aid attackers in reconnaissance or lateral movement within corporate networks. Confidentiality breaches can lead to exposure of internal infrastructure, increasing the risk of targeted attacks or data leaks. Since the vulnerability requires local access with low privileges, the threat is more significant in environments where multiple users share systems or where attackers can gain limited local access, such as through compromised credentials or insider threats. The lack of impact on integrity and availability reduces the risk of system disruption but does not diminish the importance of protecting sensitive information. Given that many European organizations still operate legacy Windows 10 versions in critical infrastructure, manufacturing, or government sectors, this vulnerability could be leveraged to gather intelligence for further attacks. The absence of known exploits reduces immediate risk but should not lead to complacency.

1. Upgrade affected systems from Windows 10 Version 1809 to a more recent, supported Windows version where this vulnerability is addressed or mitigated. 2. Apply any forthcoming security updates or patches from Microsoft as soon as they become available. 3. Restrict local access to systems running Windows 10 Version 1809 by enforcing strict access controls and monitoring for unauthorized logins. 4. Implement network segmentation to limit the exposure of DNS servers and sensitive systems to only trusted users and devices. 5. Use endpoint detection and response (EDR) tools to monitor for suspicious activities that may indicate attempts to exploit local vulnerabilities. 6. Conduct regular audits of user privileges and remove unnecessary local access rights to minimize the attack surface. 7. Educate users and administrators about the risks of running unsupported or legacy OS versions and encourage timely upgrades. 8. Employ DNS security best practices, such as DNS filtering and logging, to detect anomalous DNS queries or data exfiltration attempts.