CVE-2025-59240 is a vulnerability identified in Microsoft 365 Apps for Enterprise, specifically targeting Microsoft Excel version 16.0.1. The issue is classified under CWE-200, indicating an exposure of sensitive information to unauthorized actors. The vulnerability allows an attacker with local access to the affected system to disclose sensitive data stored or processed by Excel without requiring any privileges or authentication. However, exploitation requires user interaction, such as opening a malicious file or triggering a specific action within Excel. The CVSS v3.1 score is 5.5 (medium severity), with the vector indicating local attack vector (AV:L), low attack complexity (AC:L), no privileges required (PR:N), and user interaction required (UI:R). The impact is limited to confidentiality (C:H), with no impact on integrity or availability. No known exploits have been reported in the wild, and no official patches have been released at the time of publication. The vulnerability arises from improper handling of sensitive data within Excel, potentially allowing unauthorized disclosure of confidential information to local attackers. This could include data leakage of business-critical or personal information if an attacker gains physical or remote desktop access to a compromised machine. The vulnerability's scope is limited to local systems running the affected Excel version, and it does not extend to network-based exploitation or remote code execution. The issue was reserved in September 2025 and published in November 2025, indicating recent discovery and disclosure.

For European organizations, the primary impact of CVE-2025-59240 is the potential unauthorized disclosure of sensitive information processed or stored in Microsoft Excel. This could lead to breaches of confidentiality, especially in sectors such as finance, healthcare, legal, and government where sensitive data is prevalent. Data leakage could result in regulatory non-compliance under GDPR, leading to financial penalties and reputational damage. Since exploitation requires local access and user interaction, the risk is higher in environments where endpoint security is weak or where insider threats exist. The vulnerability does not affect system integrity or availability, so it does not directly enable data manipulation or denial of service. However, the exposure of sensitive data could facilitate further attacks or social engineering campaigns. Organizations with extensive use of Microsoft 365 Apps for Enterprise, particularly Excel, are at greater risk. The absence of known exploits in the wild provides a window for proactive mitigation. Nevertheless, the medium severity score reflects a moderate risk that should not be ignored, especially in high-value or regulated environments.

1. Restrict local access to systems running Microsoft Excel 16.0.1 by enforcing strict physical and logical access controls, including the use of strong authentication and session locking. 2. Implement application whitelisting and endpoint protection solutions to monitor and block suspicious activities related to Excel files and processes. 3. Educate users about the risks of opening untrusted Excel files and enforce policies to avoid executing unknown or unsolicited documents. 4. Monitor logs and endpoint telemetry for unusual file access patterns or attempts to extract sensitive data from Excel. 5. Until an official patch is released, consider deploying temporary workarounds such as disabling macros or limiting Excel functionality through group policies where feasible. 6. Maintain an up-to-date asset inventory to identify and prioritize systems running the affected Excel version for rapid patch deployment once available. 7. Coordinate with Microsoft support channels to receive timely updates and patches. 8. Conduct regular security awareness training emphasizing local threat vectors and insider risks. 9. Employ data loss prevention (DLP) solutions to detect and prevent unauthorized data exfiltration from endpoints. 10. Review and tighten file sharing and storage permissions to minimize exposure of sensitive Excel files.