CVE-2025-53770 is a critical security vulnerability classified under CWE-502, which pertains to the deserialization of untrusted data. This vulnerability affects Microsoft SharePoint Enterprise Server 2016, an on-premises collaboration and document management platform widely used by enterprises. The flaw allows an unauthorized attacker to execute arbitrary code remotely over a network without requiring any authentication or user interaction. The root cause lies in the way SharePoint processes serialized data inputs, which can be manipulated by attackers to inject malicious payloads during deserialization. Successful exploitation could lead to full system compromise, including complete control over the SharePoint server, access to sensitive documents, and potential lateral movement within the affected network. The vulnerability has a CVSS v3.1 base score of 9.8, indicating critical severity, with attack vector network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), and no user interaction (UI:N). Microsoft is aware of active exploits in the wild and is preparing a comprehensive patch, but currently recommends applying interim mitigations as outlined in their advisory. Given the central role of SharePoint in enterprise environments, this vulnerability poses a significant risk to confidentiality, integrity, and availability of organizational data and services.

For European organizations, the impact of CVE-2025-53770 could be severe. SharePoint is extensively used across various sectors including government, finance, healthcare, and manufacturing in Europe for document management and collaboration. Exploitation could lead to unauthorized access to sensitive personal data protected under GDPR, intellectual property theft, disruption of business operations, and reputational damage. The ability to execute code remotely without authentication increases the risk of widespread compromise, ransomware deployment, or espionage activities. Given the criticality of the vulnerability and the presence of exploits in the wild, European entities face heightened exposure, especially those with large-scale SharePoint deployments or those lacking robust network segmentation and monitoring. The potential for data breaches could also trigger regulatory penalties and legal consequences under European data protection laws.

Beyond applying the forthcoming official patch from Microsoft as soon as it is released, European organizations should implement several specific mitigations immediately: 1) Restrict network access to SharePoint servers by enforcing strict firewall rules and limiting exposure to only trusted IP addresses or VPN connections. 2) Enable and enforce strict input validation and monitoring on SharePoint endpoints to detect anomalous deserialization attempts. 3) Employ application-layer firewalls or Web Application Firewalls (WAFs) with custom rules to block suspicious serialized payloads. 4) Conduct thorough audits of SharePoint permissions and remove unnecessary administrative privileges to limit potential damage. 5) Implement network segmentation to isolate SharePoint servers from critical infrastructure and sensitive data stores. 6) Increase logging and real-time monitoring for unusual activity patterns indicative of exploitation attempts. 7) Educate IT and security teams on the indicators of compromise related to deserialization attacks. These targeted actions, combined with rapid patch deployment, will significantly reduce the risk posed by this vulnerability.