CVE-2025-62556 is a vulnerability classified under CWE-822 (Untrusted Pointer Dereference) found in Microsoft Office Online Server, specifically affecting the Excel component. The vulnerability arises when the software dereferences pointers that are not properly validated, allowing an attacker to manipulate memory references. This can lead to arbitrary code execution on the local machine where the Office Online Server is running. The vulnerability requires the attacker to have local access to the system and involves some user interaction, such as opening a malicious Excel document or triggering a specific action within the Office Online Server environment. The CVSS v3.1 base 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 on confidentiality, integrity, and availability is high (C:H/I:H/A:H), meaning successful exploitation could lead to full system compromise. The vulnerability is currently published with no known exploits in the wild and no patches released yet, which increases the urgency for organizations to prepare mitigations. The affected version is 16.0.0.0 of Microsoft Office Online Server, a widely used platform for online document collaboration and editing in enterprise environments. The flaw could be exploited by attackers who gain local access, potentially through other means such as phishing or insider threats, to escalate privileges and execute arbitrary code, compromising sensitive data and disrupting services.

For European organizations, the impact of CVE-2025-62556 could be significant due to the widespread use of Microsoft Office Online Server in enterprise and government sectors for document collaboration and productivity. Successful exploitation could lead to unauthorized code execution on critical servers, resulting in data breaches, loss of data integrity, and service outages. This could disrupt business operations, lead to regulatory non-compliance (especially under GDPR), and cause reputational damage. The requirement for local access and user interaction somewhat limits remote exploitation but does not eliminate risk, particularly in environments with weak internal access controls or where attackers have already gained footholds. Organizations handling sensitive or regulated data, such as financial institutions, healthcare providers, and public sector entities, are at higher risk. The vulnerability could also be leveraged as part of a multi-stage attack chain to escalate privileges and move laterally within networks, amplifying its impact.

1. Restrict local access to servers running Microsoft Office Online Server to trusted personnel only and enforce strict access controls and monitoring. 2. Implement application whitelisting and endpoint protection to detect and block suspicious activities related to Office Online Server processes. 3. Educate users about the risks of opening untrusted Excel documents and enforce policies to limit user interaction with potentially malicious files. 4. Monitor logs and system behavior for unusual activity indicative of exploitation attempts, such as unexpected process launches or memory access violations. 5. Prepare for rapid deployment of official patches once Microsoft releases them by maintaining an up-to-date inventory of affected systems and testing patch compatibility in advance. 6. Consider network segmentation to isolate Office Online Server infrastructure from less trusted network zones to reduce the risk of lateral movement. 7. Use multi-factor authentication and strong credential management to reduce the risk of initial local access by attackers. 8. Regularly review and update incident response plans to include scenarios involving local code execution vulnerabilities in critical collaboration platforms.