CVE-2025-59224 is a use-after-free vulnerability (CWE-416) identified in Microsoft Office Online Server, specifically within the Microsoft Office Excel component. This vulnerability arises when the software improperly manages memory, freeing an object while it is still in use, which can lead to memory corruption. An attacker exploiting this flaw can execute arbitrary code locally on the affected system. The vulnerability does not require prior authentication (PR:N) but does require user interaction (UI:R), such as opening a malicious Excel document or triggering a specific action within Office Online Server. The attack vector is local (AV:L), meaning the attacker must have local access to the system. The vulnerability impacts confidentiality, integrity, and availability (all rated high), indicating that successful exploitation could lead to full system compromise, data leakage, or denial of service. The affected version is 16.0.0.0 of Office Online Server, a product widely used in enterprise environments for hosting Office applications online. No public exploits are known at this time, but the vulnerability has been officially published and assigned a CVSS v3.1 score of 7.8, categorizing it as high severity. The vulnerability was reserved in early September 2025 and published in mid-October 2025. No patches are currently linked, indicating that organizations should prioritize monitoring and mitigation until updates are released.

For European organizations, the impact of CVE-2025-59224 can be significant, especially for enterprises and public sector entities relying on Microsoft Office Online Server for collaborative document editing and management. Successful exploitation could allow attackers to execute arbitrary code locally, potentially leading to full system compromise, unauthorized data access, or disruption of critical business processes. This could affect confidentiality by exposing sensitive documents, integrity by altering data or configurations, and availability by causing system crashes or denial of service. Given the local attack vector, insider threats or attackers who have gained limited access could leverage this vulnerability to escalate privileges or move laterally within networks. The lack of known exploits in the wild provides a window for proactive defense, but the high CVSS score and critical impact on core business applications necessitate urgent attention. Organizations in sectors such as finance, government, healthcare, and critical infrastructure are particularly at risk due to the sensitive nature of their data and regulatory requirements in Europe.

1. Monitor Microsoft’s official channels closely for the release of security patches addressing CVE-2025-59224 and apply them immediately upon availability. 2. Restrict local access to Office Online Server systems to trusted personnel only, employing strict access controls and network segmentation to limit exposure. 3. Implement application whitelisting and endpoint protection solutions capable of detecting anomalous behavior indicative of exploitation attempts. 4. Educate users about the risks of opening untrusted Excel documents or interacting with suspicious content within Office Online Server environments. 5. Conduct regular security audits and vulnerability assessments focusing on Office Online Server deployments to identify and remediate potential weaknesses. 6. Employ advanced monitoring and logging to detect unusual local activity or process execution that could signal exploitation attempts. 7. Consider deploying virtual desktop infrastructure (VDI) or sandboxing techniques to isolate Office Online Server sessions and reduce risk of local code execution. 8. Review and tighten user interaction policies, minimizing unnecessary user privileges and enforcing least privilege principles.