CVE-2025-54902 is a high-severity vulnerability identified in Microsoft Office Online Server, specifically affecting the Excel component. The vulnerability is classified as an out-of-bounds read (CWE-125), which occurs when the software reads data outside the bounds of allocated memory. This flaw can lead to unauthorized local code execution by an attacker. The vulnerability exists in version 16.0.0.0 of Office Online Server. Exploitation requires local access (Attack Vector: Local), no privileges are required (PR:N), but user interaction is necessary (UI:R). The vulnerability impacts confidentiality, integrity, and availability, all rated high. The CVSS v3.1 base score is 7.8, indicating a high severity level. The vulnerability allows an attacker to read memory beyond intended limits, potentially leading to memory corruption and execution of arbitrary code on the host machine. Although no known exploits are currently in the wild, the vulnerability's nature and impact make it a significant risk. The lack of available patches at the time of publication increases the urgency for mitigation. The vulnerability is particularly concerning because Office Online Server is often deployed in enterprise environments to provide web-based access to Office documents, including Excel spreadsheets, making it a critical component in many organizations' collaboration infrastructure.

For European organizations, this vulnerability poses a substantial risk due to the widespread use of Microsoft Office Online Server in enterprise and public sector environments. Successful exploitation could allow attackers to execute arbitrary code locally, potentially leading to data breaches, disruption of services, or lateral movement within networks. The high impact on confidentiality, integrity, and availability means sensitive corporate and personal data could be exposed or altered, and critical business operations could be interrupted. Given the reliance on Office Online Server for document collaboration, exploitation could affect productivity and trust in IT systems. Additionally, regulatory frameworks such as GDPR impose strict requirements on data protection; a breach exploiting this vulnerability could result in significant legal and financial consequences for European organizations. The requirement for local access and user interaction somewhat limits remote exploitation, but insider threats or phishing attacks could facilitate exploitation. The absence of known exploits in the wild currently provides a window for proactive defense, but the vulnerability's characteristics suggest it could be targeted in the future.

European organizations should prioritize the following mitigation steps: 1) Monitor Microsoft security advisories closely for patches addressing CVE-2025-54902 and apply updates immediately upon release. 2) Restrict local access to systems running Office Online Server to trusted personnel only, employing strict access controls and multi-factor authentication to reduce the risk of unauthorized local exploitation. 3) Implement endpoint protection solutions capable of detecting anomalous behavior indicative of exploitation attempts, including memory corruption and code execution activities. 4) Educate users about the risks of social engineering and phishing attacks that could lead to the required user interaction for exploitation, emphasizing cautious handling of Office documents and links. 5) Conduct regular security audits and penetration testing focusing on Office Online Server deployments to identify and remediate potential weaknesses. 6) Employ network segmentation to isolate Office Online Server infrastructure from critical systems, limiting potential lateral movement if exploitation occurs. 7) Utilize application whitelisting and privilege restriction to minimize the impact of any successful code execution. These measures, combined with vigilant monitoring and rapid patching, will reduce the risk posed by this vulnerability.