CVE-2025-54898 is an out-of-bounds read vulnerability classified under CWE-125, found in Microsoft Office Online Server's Excel component (version 16.0.0.0). This vulnerability allows an attacker to read memory outside the intended buffer boundaries, which can lead to the execution of arbitrary code locally on the affected system. The flaw arises from improper bounds checking when processing Excel files, enabling crafted malicious files to trigger the vulnerability. Exploitation requires the attacker to have local access and for a user to interact with a malicious Excel file through Office Online Server, which processes Excel documents for web-based collaboration. The CVSS v3.1 score of 7.8 reflects high impact on confidentiality, integrity, and availability, with low attack complexity and no privileges required, but user interaction is necessary. No public exploits are known yet, and no patches have been released at the time of publication. The vulnerability poses a significant risk in environments where Office Online Server is used to facilitate Excel document collaboration, potentially allowing attackers to execute code, steal sensitive data, or disrupt services.

For European organizations, this vulnerability could lead to unauthorized code execution on servers running Office Online Server, compromising sensitive business data and disrupting collaborative workflows. Confidentiality is at risk as attackers could access memory contents, potentially exposing sensitive information. Integrity and availability are also threatened since attackers could alter or disrupt Excel document processing, impacting business operations. Organizations in finance, government, healthcare, and critical infrastructure sectors that rely on Office Online Server for document collaboration are particularly vulnerable. The requirement for local access and user interaction limits remote exploitation but does not eliminate risk, especially in environments with weak access controls or where users may be tricked into opening malicious files. The absence of known exploits currently provides a window for mitigation, but the high severity score indicates that exploitation could have serious consequences.

1. Monitor Microsoft security advisories closely and apply patches immediately once released for Office Online Server. 2. Restrict local access to Office Online Server hosts to trusted personnel only, minimizing the attack surface. 3. Implement strict file upload and scanning policies to detect and block malicious Excel files before processing. 4. Employ network segmentation to isolate Office Online Server from critical systems and sensitive data repositories. 5. Educate users about the risks of interacting with untrusted Excel files, especially in web-based collaboration environments. 6. Use application whitelisting and endpoint protection solutions on servers hosting Office Online Server to detect anomalous behavior. 7. Regularly audit and review access logs and server activity for signs of exploitation attempts. 8. Consider disabling or limiting Excel file processing features in Office Online Server if not essential to reduce exposure.