CVE-2025-53759 is a vulnerability classified under CWE-908 (Use of Uninitialized Resource) affecting Microsoft Office Online Server, specifically version 16.0.0.0. The flaw arises from the improper initialization of a resource within Microsoft Office Excel components of the server, which can be manipulated by an unauthorized attacker to execute arbitrary code locally. This means that an attacker with local access and the ability to induce user interaction can trigger the vulnerability to gain elevated privileges or execute malicious payloads on the host system. The vulnerability has a CVSS 3.1 base score of 7.8, indicating 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). The exploitability is moderate given the local access and user interaction requirements. No known exploits have been reported in the wild, and no official patches have been released at the time of publication (August 12, 2025). The vulnerability could be leveraged in targeted attacks or insider threat scenarios to compromise sensitive data or disrupt services hosted on Office Online Server. Given the widespread use of Microsoft Office Online Server in enterprise environments, especially for collaborative document editing and sharing, this vulnerability poses a significant risk if exploited.

For European organizations, the impact of CVE-2025-53759 could be substantial. Exploitation could lead to unauthorized code execution on servers hosting Office Online Server, potentially compromising sensitive corporate or governmental documents and data. This could result in data breaches, loss of data integrity, and service disruptions affecting business continuity. Organizations relying on Office Online Server for document collaboration and workflow automation could experience operational downtime or data manipulation. The high impact on confidentiality, integrity, and availability makes this vulnerability particularly concerning for sectors handling sensitive information such as finance, healthcare, government, and critical infrastructure. Additionally, local exploitation with user interaction requirements means insider threats or compromised user accounts could be vectors for attack. The absence of a patch increases the urgency for interim mitigations to reduce exposure.

1. Restrict local access to servers running Microsoft Office Online Server to trusted personnel only and enforce strict access controls and monitoring. 2. Implement application whitelisting and endpoint protection solutions to detect and block suspicious activities related to Office Online Server processes. 3. Educate users about the risks of interacting with untrusted content or prompts on Office Online Server environments to reduce the likelihood of triggering the vulnerability. 4. Monitor system and application logs for unusual behavior or signs of exploitation attempts, focusing on Office Online Server and Excel-related processes. 5. Isolate Office Online Server instances in segmented network zones with limited access to reduce lateral movement risk. 6. Prepare for rapid deployment of official patches once released by Microsoft by maintaining an up-to-date inventory of affected systems. 7. Consider temporary disabling or limiting Excel functionalities within Office Online Server if feasible until patches are available. 8. Employ multi-factor authentication and strict privilege management to minimize the risk of unauthorized local access. These measures go beyond generic advice by focusing on access restrictions, user education, monitoring, and network segmentation tailored to the specific nature of this vulnerability.