CVE-2025-62563 is a use-after-free vulnerability classified under CWE-416 found in Microsoft Office Online Server, specifically impacting the Excel component. Use-after-free vulnerabilities occur when a program continues to use memory after it has been freed, leading to undefined behavior such as arbitrary code execution. In this case, an attacker can exploit this flaw by convincing a user to open a specially crafted Excel file via the Office Online Server interface. The vulnerability does not require any privileges or authentication but does require user interaction, such as opening or previewing the malicious file. Exploitation results in local code execution, potentially allowing the attacker to execute arbitrary code with the privileges of the user running the Office Online Server process. The CVSS v3.1 score of 7.8 reflects high impact on confidentiality, integrity, and availability, with low attack complexity and no privileges required. The vulnerability affects version 16.0.0.0 of Office Online Server, and as of the published date, no patches have been released, nor are there known exploits in the wild. This vulnerability poses a significant risk to organizations relying on Office Online Server for document collaboration and processing, as it could lead to compromise of server environments and lateral movement within networks.

For European organizations, the impact of CVE-2025-62563 is substantial. Office Online Server is widely used in enterprise environments for collaborative document editing and sharing, making it a critical component in many IT infrastructures. Successful exploitation could lead to unauthorized code execution on servers, resulting in data breaches, disruption of services, and potential spread of malware within corporate networks. Confidentiality is at risk as attackers could access sensitive documents processed by the server. Integrity and availability could also be compromised, affecting business continuity. Sectors such as finance, government, healthcare, and critical infrastructure in Europe that rely heavily on Microsoft Office Online Server are particularly vulnerable. The lack of authentication requirements and the ease of exploitation increase the likelihood of targeted attacks. Additionally, the vulnerability could be leveraged in supply chain attacks or to gain footholds in networks for further exploitation.

Immediate mitigation involves monitoring Microsoft’s security advisories for patches addressing CVE-2025-62563 and applying them as soon as they become available. Until patches are released, organizations should restrict access to Office Online Server to trusted users and networks, implement strict file upload and preview policies, and disable preview features for untrusted documents. Employ network segmentation to isolate Office Online Server from critical systems. Use endpoint detection and response (EDR) tools to monitor for suspicious activity related to Office Online Server processes. Educate users about the risks of opening untrusted Excel files, especially via online services. Consider deploying application whitelisting and enhanced memory protection techniques such as Control Flow Guard (CFG) and Data Execution Prevention (DEP) on servers hosting Office Online Server. Regularly audit and update server configurations to minimize attack surface. Finally, implement robust logging and incident response plans to quickly detect and respond to potential exploitation attempts.