CVE-2025-59232 is an out-of-bounds read vulnerability classified under CWE-125 affecting Microsoft Office Online Server, specifically the Excel component. This vulnerability arises when the software improperly reads memory outside the intended buffer boundaries during Excel file processing. An attacker with local access and the ability to induce user interaction can exploit this flaw to disclose sensitive information residing in adjacent memory locations. The vulnerability does not require any privileges (PR:N) but does require user interaction (UI:R), and the attack vector is local (AV:L), meaning the attacker must have some form of local access to the system hosting Office Online Server. The impact affects confidentiality (C:H) and availability (A:H) but not integrity (I:N), indicating that sensitive data could be leaked and the service could be disrupted or crash, but data modification is not possible through this vulnerability. The CVSS 3.1 base score is 7.1, reflecting a high severity level. The affected version is 16.0.0.0 of Microsoft Office Online Server. No patches are currently linked, and no known exploits are reported in the wild as of the publication date (October 14, 2025). The vulnerability is significant because Office Online Server is widely used in enterprise environments to provide browser-based access to Office documents, including Excel spreadsheets, which often contain sensitive business data. Exploitation could lead to unauthorized disclosure of confidential information and potential denial of service conditions. The vulnerability was reserved on September 11, 2025, and published shortly after, indicating recent discovery and disclosure.

For European organizations, this vulnerability poses a risk of sensitive data leakage from Excel files processed via Office Online Server, potentially exposing confidential business information, financial data, or personally identifiable information. The local attack vector limits remote exploitation but insider threats or compromised local accounts could leverage this flaw. The availability impact could disrupt access to Excel Online services, affecting productivity and business continuity. Organizations relying heavily on Office Online Server for collaborative document editing and sharing are particularly vulnerable. The confidentiality breach could also lead to compliance issues under GDPR if personal data is exposed. Additionally, disruption of services could impact critical sectors such as finance, government, and healthcare that use Office Online Server extensively. Since no known exploits exist yet, proactive mitigation is crucial to prevent future attacks. The vulnerability's requirement for user interaction and local access somewhat limits the attack surface but does not eliminate the risk, especially in environments with many users and complex access scenarios.

European organizations should prioritize the following mitigations: 1) Monitor Microsoft’s official channels for patches addressing CVE-2025-59232 and apply them immediately upon release. 2) Restrict local access to servers running Office Online Server to trusted personnel only, enforcing strict access controls and multi-factor authentication. 3) Implement network segmentation to isolate Office Online Server from less secure network zones, reducing the risk of local exploitation. 4) Educate users about the risks of interacting with untrusted content or files in Excel Online to minimize user interaction exploitation vectors. 5) Employ endpoint detection and response (EDR) solutions to detect anomalous local activity indicative of exploitation attempts. 6) Regularly audit and review local accounts and permissions on servers hosting Office Online Server to limit potential insider threats. 7) Consider temporary disabling or limiting Excel Online features if immediate patching is not feasible, to reduce exposure. 8) Maintain robust backup and recovery processes to mitigate availability impacts from potential crashes or denial of service. These steps go beyond generic advice by focusing on local access controls, user awareness, and network architecture adjustments specific to the nature of this vulnerability.