CVE-2025-54902 is an out-of-bounds read vulnerability classified under CWE-125 affecting Microsoft Office Online Server, specifically its Excel processing component in version 16.0.0.0. This vulnerability allows an unauthorized attacker to execute code locally by exploiting improper bounds checking during Excel file processing, leading to memory corruption. The CVSS v3.1 score of 7.8 indicates a high severity with attack vector local (AV:L), low attack complexity (AC:L), no privileges required (PR:N), but requiring user interaction (UI:R). The scope is unchanged (S:U), and the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). Although no known exploits are currently reported in the wild, the vulnerability poses a significant risk if an attacker can trick a user into opening a malicious Excel file via Office Online Server. The vulnerability is notable because it can lead to arbitrary code execution, potentially allowing attackers to take control of the affected system. The lack of available patches at the time of publication increases the urgency for mitigation. The vulnerability was reserved on 2025-07-31 and published on 2025-09-09, indicating a recent discovery. The vulnerability is particularly relevant for environments where Office Online Server is used to process Excel files, especially in enterprise or cloud-hosted settings.

For European organizations, this vulnerability could lead to significant data breaches, system compromise, and disruption of business operations due to the high impact on confidentiality, integrity, and availability. Organizations relying on Microsoft Office Online Server for collaborative document editing and Excel file processing are at risk of local code execution attacks that could be leveraged for lateral movement or privilege escalation within internal networks. Critical sectors such as finance, healthcare, government, and energy that use Office Online Server extensively could face operational disruptions and data loss. The requirement for user interaction limits remote exploitation but does not eliminate risk, especially in environments where users frequently open Excel files via Office Online Server. The absence of known exploits currently provides a window for proactive defense, but the high severity score necessitates rapid response to prevent potential exploitation. Additionally, the vulnerability could be exploited in targeted attacks or phishing campaigns leveraging malicious Excel files.

Organizations should immediately inventory their use of Microsoft Office Online Server, specifically version 16.0.0.0, and restrict access to trusted users and networks only. Until a patch is released, implement application whitelisting and endpoint protection solutions capable of detecting anomalous behavior related to Excel file processing. Educate users about the risks of opening untrusted Excel files, especially those received via email or external sources. Employ network segmentation to limit the potential spread of an exploit within the internal network. Monitor logs and alerts for unusual activity related to Office Online Server and Excel processing. Once Microsoft releases a patch, prioritize its deployment in all affected environments. Consider disabling or limiting Office Online Server Excel file processing capabilities if feasible as a temporary mitigation. Use advanced threat protection tools to scan and block malicious documents before they reach end users. Maintain up-to-date backups and incident response plans to quickly recover from potential compromises.