CVE-2025-62203 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 a pointer after the memory it points to has been freed, leading to undefined behavior including potential arbitrary code execution. In this case, an attacker can exploit this flaw by convincing a user to open a specially crafted Excel file via Office Online Server version 16.0.0.0. The vulnerability does not require prior authentication but does require user interaction, such as opening or interacting with the malicious document. Upon exploitation, the attacker can execute arbitrary code locally with the privileges of the user running the Office Online Server process, potentially leading to full system compromise. The CVSS v3.1 score of 7.8 reflects high severity due to the combination of local attack vector, low attack complexity, no privileges required, but requiring user interaction. Confidentiality, integrity, and availability impacts are all rated high, indicating that sensitive data could be exposed or altered, and system stability could be compromised. Currently, no public exploits or patches are available, but the vulnerability is officially published and should be addressed promptly. The vulnerability is particularly concerning for environments where Office Online Server is exposed to multiple users or integrated into collaborative workflows, as it increases the attack surface. The lack of patches necessitates immediate mitigation through configuration and operational controls.

For European organizations, the impact of CVE-2025-62203 can be significant, especially for enterprises and public sector entities relying on Microsoft Office Online Server for document collaboration and processing. Successful exploitation could lead to unauthorized code execution, allowing attackers to steal sensitive information, manipulate data, disrupt services, or establish persistence within the network. This is particularly critical for sectors such as finance, healthcare, government, and critical infrastructure, where data confidentiality and service availability are paramount. The vulnerability's requirement for local access and user interaction somewhat limits remote exploitation but does not eliminate risk, especially in environments where users frequently handle external or untrusted Excel files. The absence of known exploits in the wild provides a window for proactive defense, but the high severity score underscores the urgency of mitigation. Additionally, the integration of Office Online Server with other Microsoft services may amplify the impact if attackers leverage this vulnerability as a foothold for lateral movement within networks.

1. Apply patches immediately once Microsoft releases them for Office Online Server version 16.0.0.0 to address CVE-2025-62203. 2. Until patches are available, restrict local access to Office Online Server systems to trusted personnel only and enforce strict access controls. 3. Implement application whitelisting and endpoint protection solutions to detect and block suspicious code execution attempts. 4. Educate users about the risks of opening Excel files from untrusted sources and enforce policies to scan all incoming documents with updated antivirus and sandboxing tools. 5. Disable or limit features in Office Online Server that process Excel files if not required, reducing the attack surface. 6. Monitor logs and network traffic for unusual activity related to Office Online Server, including unexpected process launches or file modifications. 7. Employ network segmentation to isolate Office Online Server from critical infrastructure and sensitive data repositories. 8. Regularly review and update incident response plans to include scenarios involving exploitation of Office Online Server vulnerabilities.