CVE-2024-21356 is a medium-severity vulnerability identified in Microsoft Windows 10 Version 1809, specifically affecting the Lightweight Directory Access Protocol (LDAP) implementation. The vulnerability is classified under CWE-476, which corresponds to a NULL Pointer Dereference. This type of flaw occurs when the software attempts to read or write to a memory location through a pointer that has a NULL value, leading to unexpected behavior or system crashes. In this case, exploitation of the vulnerability can cause a Denial of Service (DoS) condition by crashing the LDAP service or potentially the entire operating system instance. The CVSS 3.1 base score is 6.5, reflecting a medium severity level, with the vector indicating that the attack can be launched remotely over the network (AV:N), requires low attack complexity (AC:L), and requires privileges (PR:L) but no user interaction (UI:N). The scope is unchanged (S:U), and the impact is limited to availability (A:H) with no confidentiality or integrity impact. No known exploits are currently reported in the wild, and no patches or mitigations have been linked yet. The vulnerability was reserved in December 2023 and published in February 2024. Since it affects Windows 10 Version 1809 (build 10.0.17763.0), which is an older version of Windows 10, systems still running this version are at risk. LDAP is a critical protocol used for directory services, authentication, and authorization in enterprise environments, so disruption can impact identity services and access controls.

For European organizations, the impact of this vulnerability could be significant in environments where Windows 10 Version 1809 is still in use, particularly in legacy systems or specialized industrial or governmental deployments that have not yet upgraded. A successful exploitation would cause denial of service on LDAP services, potentially disrupting authentication and directory lookups, which could cascade into broader service outages or access issues. This could affect internal user productivity, access to critical applications, and potentially delay incident response or security monitoring that relies on LDAP-based authentication. While the vulnerability does not directly compromise confidentiality or integrity, the availability impact alone can be disruptive, especially in sectors such as finance, healthcare, government, and critical infrastructure where directory services are foundational. The requirement for low privileges to exploit means that insider threats or compromised accounts could leverage this vulnerability to cause service disruption. The lack of user interaction needed facilitates remote exploitation, increasing risk in exposed network environments.

Given the absence of an official patch at the time of this analysis, European organizations should prioritize upgrading affected systems to a supported and patched version of Windows 10 or later. If immediate upgrade is not feasible, organizations should restrict network access to LDAP services on Windows 10 Version 1809 systems, limiting exposure to trusted internal networks only. Implement network segmentation and firewall rules to block LDAP traffic from untrusted sources. Monitor LDAP service logs and system event logs for unusual crashes or restarts indicative of exploitation attempts. Employ endpoint detection and response (EDR) tools to detect anomalous behavior related to LDAP service failures. Additionally, review and enforce the principle of least privilege to reduce the number of accounts with the ability to trigger this vulnerability. Organizations should also prepare incident response plans to quickly recover LDAP services in case of denial of service. Finally, stay alert for official patches or advisories from Microsoft and apply them promptly once available.