CVE-2025-59225 is a use-after-free vulnerability classified under CWE-416, found in Microsoft Office Online Server, specifically impacting the Excel component. The vulnerability arises when the application improperly manages memory, freeing an object while it is still in use, which can lead to arbitrary code execution. An attacker can exploit this flaw by convincing a user to open a specially crafted Excel file, triggering the use-after-free condition. This results in the attacker gaining the ability to execute code locally on the victim's machine with the same privileges as the user. The vulnerability does not require prior authentication or elevated privileges but does require user interaction, such as opening a malicious file. 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 affected version is Microsoft Office Online Server 16.0.0.0. Currently, there are no known exploits in the wild, but the vulnerability is publicly disclosed and should be addressed promptly. The lack of available patches at the time of publication necessitates interim mitigations to reduce risk.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Microsoft Office Online Server in enterprise environments. Successful exploitation could lead to local code execution, enabling attackers to escalate privileges, steal sensitive data, disrupt operations, or deploy malware. Confidentiality is at high risk as attackers could access sensitive documents processed by Office Online Server. Integrity and availability are also threatened, as attackers could modify or delete files or disrupt service availability. Sectors such as finance, government, healthcare, and critical infrastructure that rely heavily on Microsoft Office Online Server for document collaboration and processing are particularly vulnerable. The requirement for user interaction means phishing or social engineering campaigns could be used to deliver malicious files. The absence of known exploits currently reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits following public disclosure.

Organizations should prioritize deploying official patches from Microsoft as soon as they become available. Until patches are released, implement strict access controls to limit local access to systems running Office Online Server. Employ application whitelisting and endpoint protection solutions to detect and block suspicious activities related to file handling and code execution. Educate users about the risks of opening unsolicited or unexpected Excel files, emphasizing caution with email attachments and links. Monitor logs and network traffic for unusual behavior indicative of exploitation attempts. Consider isolating Office Online Server environments and restricting file upload capabilities to trusted users. Regularly update and audit security configurations to minimize attack surfaces. Additionally, implement multi-factor authentication and network segmentation to limit potential lateral movement if exploitation occurs.