CVE-2025-62203 is a use-after-free vulnerability classified under CWE-416, found in Microsoft Office Online Server's Excel component, version 16.0.0.0. Use-after-free occurs when a program continues to use memory after it has been freed, leading to undefined behavior and potential exploitation. In this case, the vulnerability allows an unauthorized attacker to execute arbitrary code locally, meaning the attacker must have local access to the system and induce some user interaction to trigger the flaw. The CVSS 3.1 base score is 7.8, indicating high severity, with the vector AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H, which means the attack requires local access, low complexity, no privileges, user interaction, unchanged scope, and impacts confidentiality, integrity, and availability to a high degree. Although no public exploits are known yet, the vulnerability poses a significant risk because successful exploitation can lead to full compromise of the affected system. The vulnerability was reserved in early October 2025 and published in November 2025, but no official patches have been released at the time of this report. Microsoft Office Online Server is widely used in enterprise environments for collaborative document editing and management, making this vulnerability particularly critical in business contexts. The lack of patches necessitates immediate mitigation strategies to reduce exposure until a fix is available.

For European organizations, the impact of CVE-2025-62203 can be substantial. Since Office Online Server is commonly deployed in enterprise and government environments for document collaboration, exploitation could lead to unauthorized code execution on critical servers, potentially compromising sensitive data and disrupting business operations. The high impact on confidentiality, integrity, and availability means attackers could steal confidential information, alter documents, or cause denial of service. Local access requirement limits remote exploitation but insider threats or attackers who gain initial footholds could leverage this vulnerability to escalate privileges or move laterally within networks. The need for user interaction suggests phishing or social engineering could be vectors to trigger the exploit. Organizations handling sensitive or regulated data, such as financial institutions, healthcare providers, and public sector entities across Europe, face heightened risks. The absence of patches increases the window of vulnerability, emphasizing the need for proactive defense measures.

1. Restrict local access to servers running Microsoft Office Online Server, ensuring only trusted administrators have physical or remote desktop access. 2. Implement strict user privilege management and monitor for unusual local user activity that could indicate exploitation attempts. 3. Employ application whitelisting and endpoint detection and response (EDR) solutions to detect and block suspicious code execution patterns. 4. Educate users about the risks of social engineering and phishing that could trigger user interaction required for exploitation. 5. Isolate Office Online Server environments from less secure network segments to limit lateral movement opportunities. 6. Regularly audit and harden server configurations, disabling unnecessary services and features that could be leveraged in attacks. 7. Prepare for rapid deployment of official patches once Microsoft releases them by maintaining an up-to-date asset inventory and patch management process. 8. Consider deploying virtual desktop infrastructure (VDI) or sandboxing techniques for users accessing Office Online Server to contain potential exploitation.