CVE-2025-62564 is an out-of-bounds read vulnerability classified under CWE-125 found in Microsoft Office Online Server, specifically affecting the Excel component in version 16.0.0.0. This vulnerability occurs due to improper bounds checking when processing Excel files, allowing an attacker to read memory outside the intended buffer boundaries. Such memory corruption can lead to arbitrary code execution locally, enabling an attacker without prior privileges to execute malicious code on the affected system. The attack vector requires local access and user interaction, such as opening a crafted Excel file, but does not require authentication or elevated privileges initially. The vulnerability impacts confidentiality, integrity, and availability by potentially exposing sensitive data, allowing code execution that could modify or destroy data, and disrupting service availability. Although no exploits have been observed in the wild yet, the high CVSS score (7.8) reflects the significant risk posed. The vulnerability was reserved in mid-October 2025 and published in early December 2025, indicating recent discovery. Microsoft Office Online Server is widely used in enterprise environments to provide browser-based Office functionality, making this vulnerability relevant for organizations relying on cloud or hybrid deployments of Microsoft Office services. The lack of available patches at the time of disclosure necessitates immediate risk mitigation and monitoring.

For European organizations, the impact of CVE-2025-62564 can be substantial. Many enterprises and public sector entities across Europe rely heavily on Microsoft Office Online Server for collaborative document editing and workflow integration. Successful exploitation could lead to local code execution, allowing attackers to escalate privileges, steal sensitive data, or disrupt critical business processes. This is particularly concerning for sectors such as finance, healthcare, government, and critical infrastructure, where data confidentiality and system integrity are paramount. The requirement for local access and user interaction somewhat limits remote exploitation, but insider threats or phishing campaigns delivering malicious Excel files could facilitate attacks. Additionally, the vulnerability could be leveraged as a foothold for lateral movement within corporate networks. The absence of known exploits currently provides a window for proactive defense, but organizations must act swiftly to prevent potential exploitation. The high severity rating underscores the need for urgent attention to protect European digital assets and maintain regulatory compliance with data protection laws such as GDPR.

1. Monitor Microsoft’s official channels closely for the release of security patches addressing CVE-2025-62564 and apply them immediately upon availability. 2. Restrict local access to systems running Office Online Server to trusted personnel only, minimizing the risk of unauthorized local exploitation. 3. Implement strict file upload and content scanning policies to detect and block malicious Excel files before they reach end users. 4. Educate users about the risks of opening unsolicited or suspicious Excel documents, emphasizing the need for caution and verification. 5. Employ endpoint detection and response (EDR) solutions to identify anomalous behavior indicative of exploitation attempts, such as unusual memory access patterns or process execution. 6. Segment networks to limit lateral movement opportunities if an attacker gains local access. 7. Conduct regular audits of Office Online Server configurations and access controls to ensure adherence to security best practices. 8. Consider deploying application whitelisting and privilege restriction to reduce the impact of potential code execution. 9. Prepare incident response plans specifically addressing local code execution scenarios involving Office Online Server. 10. Collaborate with cybersecurity information sharing groups within Europe to stay informed about emerging threats and mitigation strategies related to this vulnerability.