CVE-2025-24075 is a high-severity stack-based buffer overflow vulnerability identified in Microsoft Office Online Server, specifically affecting the Excel component. This vulnerability arises from improper handling of buffer boundaries within the software, allowing an attacker to overwrite the stack memory. Exploitation of this flaw enables an unauthorized attacker to execute arbitrary code locally on the affected system. The vulnerability does not require privileges (PR:N) but does require user interaction (UI:R), such as opening a malicious Excel file or interacting with crafted content served via Office Online Server. The attack vector is local (AV:L), meaning the attacker must have local access to the system or be able to induce the user to open malicious content. The CVSS 3.1 base score of 7.8 reflects the high impact on confidentiality, integrity, and availability, with potential for complete system compromise. The vulnerability is categorized under CWE-121, indicating a classic stack-based buffer overflow, which is a well-known and dangerous class of memory corruption bugs. As of the published date, no known exploits are reported in the wild, and no patches have been linked yet, indicating that organizations should prioritize monitoring and mitigation efforts. The vulnerability affects version 1.0.0 of Microsoft Office Online Server, a product used to provide browser-based access to Office applications, including Excel, which is widely deployed in enterprise environments for collaboration and document management.

For European organizations, the impact of CVE-2025-24075 can be significant due to the widespread use of Microsoft Office Online Server in corporate, governmental, and educational institutions. Successful exploitation can lead to local code execution, potentially allowing attackers to escalate privileges, install malware, exfiltrate sensitive data, or disrupt services. Given the integration of Office Online Server with other Microsoft services and enterprise workflows, a compromise could cascade into broader network infiltration. Confidentiality is at high risk as attackers could access sensitive documents processed through Excel Online. Integrity and availability are also threatened, as attackers could manipulate or destroy data or disrupt service availability. The requirement for user interaction limits remote exploitation but does not eliminate risk, especially in environments where users frequently open Excel files from external sources or untrusted collaborators. The lack of known exploits in the wild provides a window for proactive defense, but the high severity score necessitates urgent attention to prevent potential targeted attacks, especially in sectors handling critical or sensitive information.

Organizations should implement the following specific mitigations: 1) Immediately inventory and identify deployments of Microsoft Office Online Server version 1.0.0 to assess exposure. 2) Apply any available security updates or patches from Microsoft as soon as they are released; monitor official Microsoft security advisories closely. 3) Restrict user ability to open or interact with untrusted Excel files within Office Online Server environments by enforcing strict content filtering and attachment scanning policies. 4) Employ application whitelisting and endpoint protection solutions capable of detecting anomalous behavior indicative of exploitation attempts. 5) Harden the Office Online Server environment by limiting local user permissions and isolating the server from direct internet access where feasible. 6) Educate users on the risks of opening unexpected or suspicious Excel files, especially those received via email or external links. 7) Monitor logs and network traffic for unusual activity related to Office Online Server, including unexpected process launches or memory anomalies. 8) Consider deploying advanced threat detection tools that can identify exploitation attempts of buffer overflow vulnerabilities. These steps go beyond generic advice by focusing on environment-specific controls, user behavior, and proactive monitoring tailored to the nature of this vulnerability.