CVE-2025-24075 is a stack-based buffer overflow vulnerability classified under CWE-121, discovered in Microsoft Office Online Server version 1.0.0, specifically within the Excel processing component. This vulnerability arises when the application improperly handles input data, allowing an attacker to overwrite the stack memory. By crafting malicious Excel content or input that triggers this overflow, an attacker can execute arbitrary code locally on the affected system. The vulnerability requires local access and user interaction, meaning an attacker must convince a user to open or interact with a malicious file or content served by the Office Online Server. No prior privileges are required, increasing the risk from insider threats or compromised user accounts. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity but limited to local attack vector. Although no public exploits are currently known, the vulnerability's nature suggests potential for privilege escalation or full system compromise if exploited. The lack of available patches at the time of publication necessitates immediate risk mitigation. This vulnerability is particularly concerning for organizations that deploy Office Online Server to provide browser-based Office document editing, as it could be leveraged to compromise server infrastructure or user workstations. The vulnerability was reserved in January 2025 and published in March 2025, indicating recent discovery and disclosure.

For European organizations, the impact of CVE-2025-24075 can be significant. Office Online Server is often deployed in enterprise environments to enable collaborative document editing and sharing. A successful exploit could lead to local code execution on servers or user machines, potentially allowing attackers to escalate privileges, move laterally within networks, or exfiltrate sensitive data. Confidentiality is at high risk as attackers could access or manipulate sensitive Excel documents. Integrity and availability are also threatened since arbitrary code execution can disrupt services or corrupt data. Critical sectors such as finance, government, healthcare, and energy, which rely heavily on Microsoft Office infrastructure, could face operational disruptions or data breaches. The requirement for local access and user interaction somewhat limits remote exploitation but does not eliminate risk, especially in environments with weak endpoint security or insider threats. The absence of known exploits in the wild provides a window for proactive defense, but the lack of patches increases urgency for mitigation.

To mitigate CVE-2025-24075, European organizations should implement the following specific measures: 1) Restrict local access to systems running Office Online Server to trusted personnel only, enforcing strict access controls and monitoring. 2) Educate users about the risks of opening untrusted Excel files or interacting with suspicious content served via Office Online Server. 3) Temporarily disable or limit Office Online Server functionality where feasible until a patch is released. 4) Employ application whitelisting and endpoint protection solutions capable of detecting anomalous behavior indicative of exploitation attempts. 5) Monitor logs and system behavior for signs of buffer overflow exploitation or unusual code execution patterns. 6) Segment networks to isolate Office Online Server infrastructure from critical assets to reduce lateral movement risk. 7) Maintain up-to-date backups of critical data to enable recovery in case of compromise. 8) Stay informed on vendor advisories and apply patches promptly once available. These targeted actions go beyond generic advice by focusing on access control, user awareness, and proactive monitoring tailored to the vulnerability's characteristics.