CVE-2025-62556 is a vulnerability classified under CWE-822 (Untrusted Pointer Dereference) affecting Microsoft Office Online Server, specifically the Excel component. The flaw arises when the software dereferences pointers that can be influenced by untrusted input, leading to potential memory corruption. This can enable an attacker to execute arbitrary code locally on the system without requiring prior privileges, although user interaction is necessary to trigger the exploit. The vulnerability affects version 16.0.0.0 of Office Online Server. The CVSS v3.1 score is 7.8, indicating a high severity level, with attack vector Local (AV:L), low attack complexity (AC:L), no privileges required (PR:N), and user interaction required (UI:R). The impact metrics indicate high confidentiality, integrity, and availability impacts (C:H/I:H/A:H). No known exploits have been observed in the wild, and no patches have been published yet. The vulnerability poses a significant risk to environments where Office Online Server is deployed, especially in scenarios where users have local access and can be tricked into interacting with malicious Excel files. The flaw could lead to full system compromise, data leakage, or service disruption.

For European organizations, this vulnerability could lead to severe consequences including unauthorized code execution on servers running Office Online Server, potentially compromising sensitive business data and disrupting critical services. Given the high confidentiality, integrity, and availability impact, attackers could exfiltrate confidential information, alter or destroy data, or cause denial of service. Organizations relying heavily on Office Online Server for collaborative Excel document processing are particularly at risk. The requirement for local access and user interaction somewhat limits remote exploitation but insider threats or compromised endpoints could be leveraged to exploit this vulnerability. The lack of an available patch increases the window of exposure, necessitating immediate risk mitigation. Critical sectors such as finance, government, healthcare, and energy in Europe could face operational and reputational damage if exploited.

1. Restrict local access to systems running Office Online Server to trusted personnel only and enforce strict access controls. 2. Implement application whitelisting and endpoint protection to detect and block suspicious activities related to Excel processes. 3. Educate users about the risks of interacting with untrusted Excel files, emphasizing caution with files from unknown sources. 4. Monitor system logs and network traffic for unusual behavior indicative of exploitation attempts. 5. Prepare for rapid deployment of official patches from Microsoft once released by maintaining an up-to-date asset inventory and patch management process. 6. Consider isolating Office Online Server environments from general user networks to reduce exposure. 7. Employ multi-factor authentication and robust privilege management to limit potential lateral movement if exploitation occurs. 8. Regularly back up critical data and verify restoration procedures to mitigate impact from potential data integrity or availability attacks.