CVE-2025-21400 is a vulnerability classified under CWE-285 (Improper Authorization) affecting Microsoft SharePoint Enterprise Server 2016, specifically version 16.0.0. This vulnerability allows an attacker with limited privileges (PR:L) and requiring user interaction (UI:R) to perform remote code execution (RCE) on the affected server. The CVSS 3.1 vector indicates the attack can be carried out remotely over the network (AV:N) with low attack complexity (AC:L), but requires some level of privileges and user interaction, such as tricking a user into performing an action. The vulnerability impacts confidentiality, integrity, and availability at a high level (C:H/I:H/A:H), meaning an attacker could gain unauthorized access to sensitive information, modify or delete data, and disrupt services. The vulnerability arises from improper authorization checks within SharePoint, allowing escalation of privileges and execution of arbitrary code remotely. Although no public exploits are known at this time, the high CVSS score and the critical nature of SharePoint in enterprise environments make this a significant threat. SharePoint Enterprise Server 2016 is widely used for collaboration and document management, making it a valuable target for attackers aiming to compromise organizational data and operations. The lack of available patches at the time of publication necessitates immediate risk mitigation through access control and monitoring until official fixes are released.

For European organizations, the impact of CVE-2025-21400 could be severe. SharePoint Enterprise Server 2016 is commonly deployed in enterprises, government agencies, and educational institutions across Europe for document management and collaboration. Exploitation could lead to unauthorized disclosure of sensitive data, including intellectual property, personal data protected under GDPR, and confidential communications. Integrity of stored documents and workflows could be compromised, potentially disrupting business processes and damaging trust. Availability impacts could result in denial of service or operational downtime, affecting productivity and service delivery. Given the high CVSS score and the critical role of SharePoint in many organizations, a successful attack could have cascading effects on compliance, reputation, and financial stability. The requirement for user interaction and some privileges reduces the attack surface but does not eliminate risk, especially in environments with many users and complex permission structures. European entities with stringent data protection regulations must prioritize addressing this vulnerability to avoid regulatory penalties and data breaches.

1. Monitor Microsoft security advisories closely and apply official patches or updates for SharePoint Enterprise Server 2016 as soon as they become available. 2. Review and tighten SharePoint permissions to enforce the principle of least privilege, minimizing the number of users with elevated rights. 3. Implement network segmentation and firewall rules to restrict access to SharePoint servers only to trusted users and systems. 4. Educate users about phishing and social engineering risks to reduce the likelihood of successful user interaction exploitation. 5. Enable and analyze detailed logging and monitoring on SharePoint servers to detect unusual activities indicative of exploitation attempts. 6. Consider deploying application whitelisting and endpoint protection solutions that can detect and block suspicious code execution. 7. Conduct regular security assessments and penetration testing focused on SharePoint environments to identify and remediate configuration weaknesses. 8. If possible, isolate critical SharePoint instances or migrate to supported versions with improved security postures. 9. Develop and test incident response plans specifically addressing SharePoint compromise scenarios to ensure rapid containment and recovery.