CVE-2025-62201 is a heap-based buffer overflow vulnerability identified in Microsoft Office Online Server, specifically within the Excel processing component. This vulnerability arises when the application improperly handles memory allocation on the heap, leading to potential overwriting of adjacent memory regions. An attacker with local access can exploit this flaw by triggering a specially crafted input that causes the overflow, enabling arbitrary code execution on the affected system. The vulnerability does not require any privileges (PR:N) but does require user interaction (UI:R), such as opening a malicious Excel file or triggering a specific action within the Office Online Server environment. The CVSS v3.1 base score is 7.8, reflecting high severity due to its impact on confidentiality, integrity, and availability (all rated high). The scope remains unchanged (S:U), meaning the exploit affects only the vulnerable component without extending to other system components. Although no known exploits are currently active in the wild, the vulnerability's nature and impact make it a significant risk. The affected version is 16.0.0.0 of Microsoft Office Online Server, a widely used enterprise product for hosting and managing Office documents online. The lack of an available patch increases the urgency for organizations to implement interim mitigations. This vulnerability is classified under CWE-122, indicating a classic heap-based buffer overflow issue, which is a common and well-understood software weakness that can lead to arbitrary code execution if exploited successfully.

For European organizations, this vulnerability poses a substantial risk due to the widespread use of Microsoft Office Online Server in enterprise environments for document collaboration and processing. Successful exploitation could lead to local code execution, allowing attackers to escalate privileges, steal sensitive data, disrupt business operations, or deploy ransomware. The impact on confidentiality, integrity, and availability is high, potentially affecting critical business functions reliant on Excel processing. Organizations in sectors such as finance, government, healthcare, and manufacturing, which heavily utilize Office Online Server for document workflows, are particularly vulnerable. The requirement for local access and user interaction somewhat limits remote exploitation, but insider threats or compromised endpoints could still leverage this vulnerability. The absence of known exploits in the wild provides a window for proactive defense, but the lack of a patch means organizations must rely on compensating controls to mitigate risk. Given the interconnected nature of European enterprises and regulatory requirements like GDPR, a breach exploiting this vulnerability could also lead to significant compliance and reputational consequences.

1. Restrict local access to systems running Microsoft Office Online Server to trusted personnel only, employing strict access controls and monitoring. 2. Implement application whitelisting and endpoint protection solutions to detect and block suspicious activities related to Excel processing. 3. Educate users about the risks of interacting with untrusted Excel files or links, emphasizing cautious behavior to reduce the likelihood of triggering the vulnerability. 4. Use network segmentation to isolate Office Online Server environments from less secure network zones, limiting lateral movement opportunities. 5. Monitor system logs and security alerts for unusual behavior indicative of exploitation attempts, such as unexpected process executions or memory anomalies. 6. Prepare for rapid deployment of patches once Microsoft releases an official fix, including testing and validation in controlled environments. 7. Consider deploying virtual desktop infrastructure (VDI) or sandboxing techniques to contain potential exploitation impacts. 8. Regularly update and audit security policies related to Office Online Server usage and endpoint security configurations. These measures go beyond generic advice by focusing on access control, user behavior, and environment segmentation tailored to the specific exploitation vector of this vulnerability.