CVE-2025-54897 is a high-severity vulnerability identified in Microsoft SharePoint Enterprise Server 2016 (version 16.0.0). The issue stems from the deserialization of untrusted data, classified under CWE-502. Deserialization vulnerabilities occur when an application processes serialized data from untrusted sources without sufficient validation, allowing attackers to manipulate the data to execute arbitrary code. In this case, an authorized attacker—meaning someone with legitimate access but potentially limited privileges—can exploit this vulnerability remotely over a network to execute arbitrary code on the affected SharePoint server. The CVSS v3.1 base score of 8.8 reflects the critical nature of this vulnerability, with high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). The attack vector is network-based (AV:N), requires low attack complexity (AC:L), and only requires privileges (PR:L) but no user interaction (UI:N). The scope is unchanged (S:U), meaning the exploit affects the same security scope. No known exploits are currently reported in the wild, and no official patches have been linked yet. However, the vulnerability's nature suggests that once exploited, it could allow attackers to gain control over SharePoint servers, potentially leading to data breaches, service disruption, or lateral movement within enterprise networks. Given SharePoint's role in document management and collaboration, exploitation could expose sensitive corporate data or disrupt business operations.

For European organizations, the impact of CVE-2025-54897 could be significant. SharePoint is widely used across various sectors including government, finance, healthcare, and manufacturing, all of which handle sensitive data and require high availability. Exploitation could lead to unauthorized access to confidential documents, intellectual property theft, and disruption of critical collaboration services. This could result in regulatory non-compliance issues under GDPR due to data breaches, financial losses from operational downtime, and reputational damage. Additionally, attackers gaining code execution on SharePoint servers could pivot to other internal systems, amplifying the impact. The requirement for an authorized user limits the attack surface but does not eliminate risk, especially in environments with many users or where credentials may be compromised. The lack of user interaction needed means exploitation can be automated once access is obtained, increasing risk in large organizations.

European organizations should prioritize the following mitigations: 1) Implement strict access controls and least privilege principles to limit who can authenticate to SharePoint servers, reducing the pool of potential attackers. 2) Monitor and audit SharePoint access logs for unusual activity, especially from authorized users performing unexpected actions. 3) Apply network segmentation to isolate SharePoint servers from other critical infrastructure, limiting lateral movement if exploited. 4) Deploy application-layer firewalls or web application firewalls (WAFs) with rules designed to detect and block suspicious deserialization payloads or anomalous SharePoint traffic patterns. 5) Maintain up-to-date backups of SharePoint data and configurations to enable rapid recovery in case of compromise. 6) Engage with Microsoft support channels to obtain patches or workarounds as they become available, and test these in controlled environments before deployment. 7) Educate users on credential security to prevent unauthorized access via compromised accounts. 8) Consider deploying endpoint detection and response (EDR) solutions on SharePoint servers to detect post-exploitation behaviors.