CVE-2025-27746 is a high-severity use-after-free vulnerability (CWE-416) found in Microsoft Office Online Server version 1.0.0. This vulnerability arises when the application improperly manages memory, specifically by referencing memory after it has been freed. An unauthorized attacker can exploit this flaw to execute arbitrary code locally on the affected system. The vulnerability requires local access (Attack Vector: Local), does not require privileges (Privileges Required: None), but does require user interaction (User Interaction: Required). The scope is unchanged, meaning the vulnerability affects only the vulnerable component without impacting other components. The impact on confidentiality, integrity, and availability is high, indicating that successful exploitation could lead to full system compromise, including data theft, modification, or denial of service. Although no known exploits are currently in the wild, the vulnerability's high CVSS score (7.8) and critical impact make it a significant risk. The lack of available patches at the time of publication increases the urgency for mitigation. The vulnerability was reserved in early March 2025 and published in April 2025, indicating recent discovery and disclosure. The technical root cause is a use-after-free condition, a common memory corruption issue that can be leveraged for code execution by manipulating the program's memory management. Given that Office Online Server is used to provide web-based access to Microsoft Office documents, exploitation could allow attackers to compromise servers that handle sensitive document processing and collaboration.

For European organizations, this vulnerability poses a substantial risk, especially for enterprises and public sector entities relying on Microsoft Office Online Server for document collaboration and processing. Successful exploitation could lead to unauthorized code execution on servers, potentially resulting in data breaches, disruption of document services, and lateral movement within internal networks. Confidential business information and personal data protected under GDPR could be exposed or manipulated, leading to regulatory penalties and reputational damage. The requirement for local access and user interaction somewhat limits remote exploitation but does not eliminate risk, as attackers with limited access (e.g., through phishing or compromised internal accounts) could leverage this flaw. The high impact on confidentiality, integrity, and availability means that critical business operations could be disrupted, affecting productivity and trust in digital collaboration tools. Additionally, the absence of known exploits currently provides a window for proactive mitigation before widespread attacks emerge.

European organizations should prioritize the following specific mitigation steps: 1) Immediately inventory and identify any deployments of Microsoft Office Online Server version 1.0.0 within their environment. 2) Restrict local access to Office Online Server hosts strictly to trusted administrators and users, employing network segmentation and access controls to minimize exposure. 3) Implement strict user interaction policies and educate users about the risks of interacting with untrusted content or prompts on Office Online Server interfaces. 4) Monitor logs and system behavior for unusual activity indicative of exploitation attempts, such as unexpected process launches or memory anomalies. 5) Apply any available security updates or patches from Microsoft as soon as they are released; if no patches are currently available, consider temporary mitigation such as disabling or isolating vulnerable Office Online Server instances. 6) Employ endpoint protection solutions capable of detecting exploitation techniques related to use-after-free vulnerabilities. 7) Conduct regular vulnerability assessments and penetration testing focused on Office Online Server to identify and remediate potential attack vectors. 8) Coordinate with Microsoft support channels for guidance and early access to patches or workarounds.