CVE-2025-59240 is a vulnerability classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) affecting Microsoft Office LTSC 2021, specifically the Excel component version 16.0.1. The vulnerability allows an attacker with local access to the affected system to disclose sensitive information without requiring any privileges (PR:N) but does require user interaction (UI:R), such as opening a crafted Excel file or triggering a specific action within Excel. The attack vector is local (AV:L), meaning remote exploitation is not possible without prior access. The vulnerability does not impact integrity or availability, focusing solely on confidentiality (C:H, I:N, A:N). The CVSS v3.1 base score is 5.5, indicating medium severity. No known exploits have been reported in the wild, and no patches have been published at the time of analysis. The vulnerability likely arises from improper handling of sensitive data within Excel, potentially exposing data stored in memory or temporary files to unauthorized local users. Given the nature of the vulnerability, it is primarily a risk in environments where multiple users share systems or where local attackers can gain access to user sessions. The vulnerability 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 or confidential information stored or processed within Microsoft Excel files on affected systems. This could include intellectual property, financial data, or personal data protected under GDPR, leading to compliance risks and reputational damage. Since exploitation requires local access and user interaction, the threat is more significant in environments with shared workstations, insufficient endpoint security, or insider threats. The lack of impact on integrity and availability reduces the risk of operational disruption but does not diminish the confidentiality concerns. Organizations in sectors such as finance, government, healthcare, and critical infrastructure, where sensitive data is handled extensively in Excel, are particularly at risk. The absence of known exploits and patches means organizations must proactively manage risk until updates are available. Failure to mitigate could result in data breaches and regulatory penalties under European data protection laws.

1. Restrict local access to systems running Microsoft Office LTSC 2021, especially version 16.0.1, to trusted users only. 2. Implement strict user session controls and endpoint security measures to prevent unauthorized local access or privilege escalation. 3. Educate users about the risks of opening untrusted Excel files and enforce policies to avoid executing unknown or suspicious documents. 4. Monitor systems for unusual file access or process behavior related to Excel to detect potential exploitation attempts. 5. Once Microsoft releases patches or updates addressing CVE-2025-59240, prioritize immediate deployment across all affected systems. 6. Employ data encryption and data loss prevention (DLP) solutions to minimize exposure of sensitive information even if local access is compromised. 7. Conduct regular audits of shared workstations and implement session timeout policies to reduce the window of opportunity for local attackers. 8. Consider application whitelisting or sandboxing Excel to limit the impact of malicious files or actions. These measures go beyond generic advice by focusing on local access control, user behavior, and proactive monitoring tailored to the vulnerability's characteristics.