CVE-2025-59221 is a use-after-free vulnerability classified under CWE-416 affecting Microsoft SharePoint Enterprise Server 2016 (version 16.0.0). The flaw exists in the way Microsoft Office Word components handle memory, leading to a condition where previously freed memory is accessed. This can cause unpredictable behavior including the potential execution of arbitrary code by an attacker. The vulnerability requires local access to the system, a high level of attack complexity, no prior privileges, and user interaction, such as opening a malicious document or triggering a specific action within SharePoint that invokes Word processing. Exploitation could allow an attacker to execute code with the privileges of the user running the application, potentially leading to full system compromise. The CVSS 3.1 vector indicates local attack vector (AV:L), high attack complexity (AC:H), no privileges required (PR:N), user interaction required (UI:R), unchanged scope (S:U), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). No public exploits or patches are currently available, but the vulnerability has been officially published and reserved by Microsoft. This vulnerability is significant because SharePoint is widely used in enterprise environments for collaboration and document management, and the involvement of Office Word components increases the attack surface. The use-after-free condition is a common memory corruption issue that can be leveraged for code execution, often leading to privilege escalation or persistent compromise if exploited successfully.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Microsoft SharePoint Enterprise Server 2016 in corporate, governmental, and critical infrastructure sectors. Exploitation could lead to unauthorized code execution on affected systems, potentially resulting in data breaches, disruption of collaboration services, and compromise of sensitive information. The high impact on confidentiality, integrity, and availability means attackers could steal data, alter documents, or disrupt business operations. Given the local access requirement, insider threats or attackers who have gained initial footholds could leverage this vulnerability to escalate privileges or move laterally within networks. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as attackers often develop exploits after public disclosure. European organizations with remote or hybrid work environments may face increased risk if endpoint devices running SharePoint components are not adequately secured. The vulnerability also threatens compliance with data protection regulations such as GDPR if exploited to leak personal or sensitive data.

1. Monitor Microsoft security advisories closely and apply official patches or updates for SharePoint Enterprise Server 2016 as soon as they become available. 2. Restrict local access to SharePoint servers and workstations running Office Word components to trusted personnel only, using strict access controls and network segmentation. 3. Implement application whitelisting and endpoint protection solutions capable of detecting anomalous behavior related to memory corruption or code execution attempts. 4. Educate users about the risks of opening untrusted documents or links that could trigger user interaction required for exploitation. 5. Conduct regular security audits and vulnerability assessments focusing on SharePoint environments and Office integrations. 6. Employ intrusion detection systems (IDS) and endpoint detection and response (EDR) tools to identify suspicious activities indicative of exploitation attempts. 7. Limit the privileges of users running SharePoint and Office Word components to the minimum necessary to reduce potential impact. 8. Consider isolating or sandboxing document processing workflows to contain potential exploitation. 9. Maintain comprehensive backups and incident response plans tailored to SharePoint environments to enable rapid recovery if exploitation occurs.