CVE-2024-21426 is a high-severity vulnerability classified as a Use After Free (CWE-416) in Microsoft SharePoint Enterprise Server 2016, specifically version 16.0.0. This vulnerability allows remote code execution (RCE) through a flaw in the way SharePoint handles memory, where an object is accessed after it has been freed. An attacker can exploit this vulnerability remotely with low attack complexity and no privileges required, but user interaction is necessary. Successful exploitation could lead to full compromise of the affected SharePoint server, allowing an attacker to execute arbitrary code with the privileges of the SharePoint service, potentially leading to complete system takeover. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability. The vulnerability was published on March 12, 2024, and no known exploits are currently reported in the wild. The vulnerability is notable because SharePoint is widely used in enterprise environments for collaboration and document management, making it a valuable target for attackers aiming to disrupt business operations or steal sensitive information.

For European organizations, the impact of this vulnerability could be significant due to the widespread use of Microsoft SharePoint Enterprise Server 2016 in government, financial, healthcare, and large corporate sectors. Exploitation could lead to unauthorized access to sensitive documents, disruption of collaboration services, and potential lateral movement within networks. Given the high confidentiality, integrity, and availability impacts, organizations could face data breaches, operational downtime, and reputational damage. The requirement for user interaction might limit mass exploitation but targeted phishing or social engineering campaigns could facilitate attacks. Additionally, regulatory frameworks such as GDPR impose strict data protection requirements, so exploitation leading to data leakage could result in severe legal and financial penalties for European entities.

To mitigate this vulnerability, European organizations should prioritize patching SharePoint Enterprise Server 2016 to the latest security updates provided by Microsoft as soon as they become available. In the absence of an official patch at the time of this report, organizations should implement strict network segmentation to limit access to SharePoint servers, enforce least privilege principles on service accounts, and monitor for unusual activity indicative of exploitation attempts. Employing web application firewalls (WAFs) with rules targeting SharePoint-specific attack patterns can provide additional protection. User awareness training to reduce the risk of social engineering and phishing attacks that could trigger exploitation is also critical. Regularly auditing SharePoint configurations and applying security hardening best practices will reduce the attack surface. Finally, organizations should maintain comprehensive logging and incident response capabilities to detect and respond to potential exploitation attempts promptly.