CVE-2025-49711 is a high-severity use-after-free vulnerability (CWE-416) identified 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 platform. A use-after-free flaw occurs when a program continues to use a pointer after the memory it points to has been freed, potentially allowing an attacker to execute arbitrary code. In this case, an unauthorized attacker can exploit this vulnerability to execute code locally on the affected system. The CVSS 3.1 base score of 7.8 reflects the high impact on confidentiality, integrity, and availability, 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). The exploitability is currently unknown (E:U), and no known exploits are reported in the wild. The vulnerability was published on July 8, 2025, with the reservation date on June 9, 2025. No patches or mitigations have been linked yet, indicating that organizations using this product version remain exposed. The vulnerability allows an attacker who can trick a user into interacting with a maliciously crafted Excel file or content served via Office Online Server to execute arbitrary code locally, potentially leading to full system compromise or lateral movement within a network.

For European organizations, the impact of CVE-2025-49711 could be significant, especially for enterprises and public sector entities relying on Microsoft Office Online Server for collaborative document editing and sharing. Successful exploitation could lead to unauthorized code execution, resulting in data breaches, disruption of business operations, and potential compromise of sensitive information. Given the high impact on confidentiality, integrity, and availability, attackers could deploy ransomware, steal intellectual property, or disrupt critical services. The requirement for local access and user interaction somewhat limits remote exploitation but does not eliminate risk, as phishing or social engineering could facilitate user interaction. Organizations in sectors such as finance, government, healthcare, and critical infrastructure in Europe, which often use Microsoft Office Online Server, may face increased risk. Additionally, the lack of available patches increases exposure time, emphasizing the need for proactive mitigation.

1. Immediate mitigation should include restricting access to Microsoft Office Online Server instances to trusted internal networks and VPNs to reduce exposure. 2. Implement strict user awareness training to prevent social engineering attacks that could trick users into interacting with malicious Excel content. 3. Employ application whitelisting and endpoint protection solutions capable of detecting anomalous behavior indicative of exploitation attempts. 4. Monitor logs and network traffic for unusual activity related to Office Online Server and Excel processes. 5. Disable or limit features that allow uploading or rendering of Excel files from untrusted sources until a patch is available. 6. Engage with Microsoft support channels to obtain early access to patches or workarounds once released. 7. Consider deploying sandboxing or isolated environments for handling Office Online Server content to contain potential exploitation. 8. Regularly update and patch all related software components as updates become available to reduce attack surface.