CVE-2025-62201 is a heap-based buffer overflow vulnerability classified under CWE-122, affecting Microsoft Office Online Server version 16.0.0.0, specifically the Excel component. The flaw arises from improper handling of memory buffers during Excel file processing, which can lead to memory corruption. This corruption allows an attacker to execute arbitrary code locally 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 interacting with a crafted document served via Office Online Server. The attack vector is local (AV:L), meaning the attacker must have local access or convince a user to perform an action. The vulnerability impacts confidentiality, integrity, and availability (C:H/I:H/A:H), potentially allowing full system compromise. The CVSS v3.1 score is 7.8, indicating high severity. No patches or known exploits are currently available, but the vulnerability is publicly disclosed and should be considered a significant risk. Given the nature of Office Online Server as a collaborative platform, exploitation could affect multiple users and systems if leveraged in a networked environment.

For European organizations, this vulnerability could lead to severe consequences including unauthorized code execution on servers hosting Office Online Server, potentially compromising sensitive corporate data and disrupting business operations. Since Office Online Server is often deployed in enterprise environments for collaborative document editing, exploitation could allow attackers to pivot within internal networks, escalate privileges, or deploy ransomware. The confidentiality of sensitive documents could be breached, integrity of data altered, and availability of collaboration services disrupted. Organizations in sectors such as finance, government, healthcare, and critical infrastructure are particularly at risk due to the reliance on Microsoft Office products and the sensitivity of their data. The requirement for user interaction limits remote exploitation but does not eliminate risk, especially in environments where users frequently open Excel files from external sources. The lack of patches increases exposure until mitigations or updates are released.

1. Implement strict access controls to limit local access to Office Online Server hosts, reducing the risk of local exploitation. 2. Educate users to avoid opening untrusted or unexpected Excel files, especially those received via email or external sources. 3. Employ application whitelisting and endpoint protection solutions capable of detecting anomalous behavior related to buffer overflow exploitation. 4. Monitor logs and network traffic for unusual activity around Office Online Server and Excel file processing. 5. Isolate Office Online Server environments from critical infrastructure where possible to limit lateral movement. 6. Prepare for rapid deployment of official patches once released by Microsoft by maintaining an up-to-date asset inventory and patch management process. 7. Consider deploying virtual desktop infrastructure (VDI) or sandboxing solutions to contain potential exploitation impacts. 8. Regularly review and update incident response plans to include scenarios involving Office Online Server compromise.