CVE-2025-30378 is a high-severity vulnerability classified under CWE-502, which involves the deserialization of untrusted data in Microsoft SharePoint Enterprise Server 2016 (version 16.0.0). Deserialization vulnerabilities occur when an application processes serialized data from untrusted sources without proper validation, allowing attackers to manipulate the data to execute arbitrary code. In this case, the vulnerability allows an unauthorized attacker to execute code locally on the affected SharePoint server. The CVSS 3.1 base score is 7.0, indicating a high severity level. The vector string (AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H) reveals that the attack requires local access (AV:L), high attack complexity (AC:H), no privileges (PR:N), and user interaction (UI:R). The scope remains unchanged (S:U), but the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). This suggests that if exploited, the attacker could fully compromise the SharePoint server, potentially leading to data breaches, service disruption, or further lateral movement within the network. No known exploits are currently reported in the wild, and no patches have been linked yet, indicating that organizations should prioritize monitoring and mitigation efforts. The vulnerability was reserved in March 2025 and published in May 2025, reflecting recent discovery and disclosure.

For European organizations, this vulnerability poses a significant risk, especially those relying on Microsoft SharePoint Enterprise Server 2016 for document management, collaboration, and internal communications. Successful exploitation could lead to unauthorized code execution on SharePoint servers, potentially resulting in data theft, unauthorized access to sensitive corporate information, disruption of business operations, and the spread of malware within enterprise networks. Given SharePoint's role in managing critical business content, the compromise could affect confidentiality, integrity, and availability of corporate data. Additionally, since the attack requires local access and user interaction, insider threats or social engineering attacks could be leveraged by adversaries. The high impact on availability could disrupt workflows and collaboration, leading to operational downtime. The lack of known exploits in the wild provides a window for proactive defense, but organizations must act swiftly to prevent exploitation, especially in sectors with stringent data protection requirements such as finance, healthcare, and government within Europe.

To mitigate this vulnerability effectively, European organizations should: 1) Immediately audit and restrict local access to SharePoint servers, ensuring only trusted administrators and users have physical or remote local access. 2) Implement strict user training and awareness programs to reduce the risk of social engineering that could trigger the required user interaction for exploitation. 3) Monitor SharePoint server logs and system behavior for unusual activities indicative of attempted deserialization attacks or unauthorized code execution. 4) Employ application whitelisting and endpoint protection solutions capable of detecting and blocking suspicious code execution on SharePoint servers. 5) Segregate SharePoint servers within secure network zones with limited access to reduce attack surface. 6) Stay alert for official patches or updates from Microsoft and apply them promptly once available. 7) Consider upgrading to a more recent and supported version of SharePoint that may have improved security controls against deserialization vulnerabilities. 8) Conduct penetration testing and vulnerability assessments focusing on deserialization attack vectors to identify and remediate weaknesses proactively.