CVE-2025-54898 is an out-of-bounds read vulnerability classified under CWE-125, discovered in Microsoft Office Online Server's Excel component, version 16.0.0.0. This vulnerability arises from improper bounds checking when processing Excel files, allowing an attacker to read memory outside the intended buffer. Such memory corruption can lead to arbitrary code execution 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 through the Office Online Server interface. The attack vector is local (AV:L), meaning the attacker must have local access to the system hosting the Office Online Server. The vulnerability impacts confidentiality, integrity, and availability (all rated high), indicating that successful exploitation could lead to full system compromise, data leakage, or service disruption. Although no public exploits are known at this time, the vulnerability's nature and high CVSS score (7.8) suggest that it is a significant risk once weaponized. The lack of available patches at the time of publication increases exposure. Microsoft Office Online Server is widely used in enterprise environments to provide browser-based access to Office documents, making this vulnerability particularly relevant for organizations relying on this service for document collaboration and processing.

For European organizations, the impact of CVE-2025-54898 can be substantial. Exploitation could lead to unauthorized code execution on servers hosting Office Online Server, potentially compromising sensitive corporate data and disrupting document collaboration workflows. Given the high confidentiality and integrity impact, attackers could exfiltrate sensitive information or alter documents, leading to data breaches or misinformation. Availability impact means that critical services could be disrupted, affecting business continuity. Organizations in sectors such as finance, government, healthcare, and critical infrastructure, which heavily rely on Microsoft Office Online Server for document management, are particularly vulnerable. The requirement for local access limits remote exploitation but does not eliminate risk, as insider threats or compromised internal systems could be leveraged. Additionally, the lack of patches at the time of disclosure means organizations must implement interim controls to mitigate risk until updates are available.

1. Monitor Microsoft security advisories closely and apply official patches immediately once released to remediate the vulnerability. 2. Restrict local access to servers running Office Online Server by enforcing strict network segmentation and access control policies, limiting who can interact with these systems. 3. Implement application whitelisting and endpoint protection on Office Online Server hosts to detect and prevent unauthorized code execution. 4. Educate users about the risks of opening untrusted Excel files, especially via Office Online Server interfaces, to reduce the likelihood of user interaction exploitation. 5. Employ robust logging and monitoring to detect anomalous activities related to Office Online Server, including unusual file access or process execution. 6. Consider deploying additional security layers such as sandboxing or containerization for Office Online Server environments to contain potential exploitation. 7. Conduct regular security assessments and penetration testing focused on Office Online Server deployments to identify and remediate configuration weaknesses.