CVE-2025-47165 is a high-severity use-after-free vulnerability (CWE-416) found in Microsoft Office Online Server, specifically affecting version 1.0.0. This vulnerability arises from improper memory management within the Microsoft Office Excel component of the Office Online Server, where an object is freed but subsequently accessed, leading to undefined behavior. An unauthorized attacker can exploit this flaw to execute arbitrary code locally on the affected system. The CVSS 3.1 base score of 7.8 reflects a high impact, with the vector indicating local attack vector (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’s nature allows attackers to potentially gain full control over the affected system if successfully exploited. The lack of available patches at the time of publication increases the urgency for mitigation. This vulnerability is particularly critical because Office Online Server is often deployed in enterprise environments to provide browser-based access to Office documents, making it a valuable target for attackers aiming to compromise internal networks or escalate privileges within an organization.

For European organizations, the impact of CVE-2025-47165 could be significant. Office Online Server is widely used in enterprises and public sector institutions across Europe to facilitate collaborative document editing and sharing. Exploitation of this vulnerability could lead to unauthorized code execution on servers hosting Office Online Server, potentially allowing attackers to access sensitive corporate or governmental data, disrupt services, or move laterally within networks. Given the high confidentiality, integrity, and availability impacts, successful exploitation could result in data breaches, operational downtime, and reputational damage. Furthermore, since the vulnerability requires only local access and user interaction, phishing or social engineering campaigns could be used to trick users into triggering the exploit, increasing the risk. The absence of known exploits in the wild currently provides a window for proactive defense, but organizations should not be complacent given the high severity and potential for rapid weaponization.

European organizations should implement a multi-layered mitigation strategy: 1) Immediate risk reduction can be achieved by restricting access to Office Online Server to trusted users and networks only, minimizing exposure to untrusted parties. 2) Employ application whitelisting and endpoint protection solutions capable of detecting anomalous behavior related to use-after-free exploitation attempts. 3) Educate users about the risks of interacting with untrusted Office documents or links, emphasizing caution to reduce the likelihood of user interaction-based exploitation. 4) Monitor logs and network traffic for unusual activities around Office Online Server instances, including unexpected process executions or memory anomalies. 5) Since no patches are currently available, organizations should engage with Microsoft support channels for any available workarounds or advisories and plan for rapid deployment of official patches once released. 6) Consider isolating Office Online Server environments using virtualization or containerization to limit the blast radius of any successful exploit. 7) Regularly update and harden the underlying operating system and related software to reduce the attack surface.