CVE-2025-53770 is a critical security vulnerability classified under CWE-502 (Deserialization of Untrusted Data) affecting Microsoft SharePoint Enterprise Server 2016 (version 16.0.0). This vulnerability allows an unauthenticated attacker to send specially crafted serialized data to the SharePoint server, which improperly deserializes this data, leading to remote code execution (RCE) over the network. The exploit requires no user interaction or privileges, making it highly dangerous and easy to exploit. The vulnerability impacts the confidentiality, integrity, and availability of affected systems, as attackers can execute arbitrary code, potentially gaining full control over the SharePoint server and the underlying infrastructure. Microsoft has acknowledged the existence of exploits in the wild and is actively developing a comprehensive patch. Until the patch is released, Microsoft recommends applying specific mitigations detailed in the CVE documentation to reduce exposure. The vulnerability's CVSS 3.1 score of 9.8 reflects its critical nature, with attack vector network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), and no user interaction (UI:N). The scope is unchanged (S:U), but the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). This vulnerability poses a significant threat to organizations relying on on-premises SharePoint 2016 deployments, especially those with internet-facing or poorly segmented SharePoint servers.

For European organizations, the impact of CVE-2025-53770 is severe. SharePoint Enterprise Server 2016 is widely used in enterprise environments for collaboration, document management, and intranet portals. Exploitation could lead to full system compromise, allowing attackers to steal sensitive data, disrupt business operations, deploy ransomware, or use the compromised server as a foothold for lateral movement within corporate networks. Given the critical nature of SharePoint in many European government, financial, healthcare, and industrial sectors, successful exploitation could result in significant data breaches, regulatory penalties under GDPR, and operational downtime. The vulnerability's ease of exploitation and lack of required authentication increase the risk of widespread attacks, particularly targeting organizations with internet-exposed SharePoint servers or insufficient network segmentation. The potential for espionage, sabotage, or financial fraud is heightened in the current geopolitical climate, where cyberattacks against European critical infrastructure have increased.

European organizations should immediately implement the following mitigations: 1) Restrict network access to SharePoint Enterprise Server 2016 instances by limiting exposure to trusted internal networks and using firewalls or VPNs to block unauthorized external access. 2) Apply any interim configuration changes or workarounds recommended by Microsoft in the CVE advisory to disable or restrict deserialization functionality where possible. 3) Monitor network and system logs for unusual activity indicative of exploitation attempts, such as unexpected serialized data traffic or anomalous process execution. 4) Conduct thorough vulnerability assessments and penetration tests focused on SharePoint environments to identify exposure. 5) Prepare for rapid deployment of the forthcoming Microsoft patch by establishing testing and deployment procedures to minimize downtime. 6) Educate IT and security teams about the vulnerability and ensure incident response plans include scenarios involving SharePoint compromise. 7) Consider network segmentation to isolate SharePoint servers from critical systems to limit lateral movement in case of compromise. 8) Employ endpoint detection and response (EDR) solutions capable of detecting suspicious code execution patterns related to deserialization exploits.