CVE-2026-21514 is a vulnerability classified under CWE-807, indicating reliance on untrusted inputs in a security decision within Microsoft Office Word, part of Microsoft 365 Apps for Enterprise. This flaw allows an unauthorized local attacker to bypass security features by manipulating inputs that the application trusts incorrectly. The vulnerability affects version 16.0.1 of the software and does not require any privileges or elevated permissions to exploit, but it does require user interaction, such as opening a malicious document. The CVSS 3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity and no privileges required. The vulnerability could allow attackers to execute arbitrary code or escalate privileges locally, potentially leading to full system compromise. No public exploits are known yet, but the functional impact and ease of exploitation make it a critical issue for organizations relying on Microsoft 365 Apps. The vulnerability was reserved at the end of 2025 and published in early 2026, indicating recent discovery and disclosure. The lack of available patches at the time of reporting means organizations must rely on interim mitigations until updates are released. This vulnerability highlights the risks of trusting unvalidated inputs in security decisions within widely used productivity software.

For European organizations, the impact of CVE-2026-21514 is significant due to the widespread use of Microsoft 365 Apps for Enterprise across public and private sectors. Successful exploitation can lead to unauthorized local privilege escalation, enabling attackers to bypass security controls, execute arbitrary code, and potentially gain full control over affected systems. This compromises sensitive data confidentiality, system integrity, and availability of critical business applications. Sectors such as finance, healthcare, government, and critical infrastructure are particularly vulnerable due to their reliance on Microsoft Office tools and the sensitivity of their data. The local attack vector means insider threats or compromised endpoints pose a high risk. The requirement for user interaction (e.g., opening a malicious document) suggests phishing or social engineering could be used to trigger exploitation, increasing the attack surface. The absence of known exploits currently provides a window for proactive defense, but the high severity score underscores the urgency for mitigation. Disruption or data breaches resulting from exploitation could lead to regulatory penalties under GDPR and damage organizational reputation.

1. Monitor Microsoft security advisories closely and apply official patches immediately upon release to remediate the vulnerability. 2. Until patches are available, restrict local access to systems running Microsoft 365 Apps for Enterprise to trusted users only, minimizing the risk of local exploitation. 3. Implement application whitelisting and endpoint detection and response (EDR) solutions to detect and block suspicious activities related to document handling and code execution. 4. Educate users on the risks of opening unsolicited or suspicious documents, emphasizing phishing awareness to reduce the likelihood of triggering the vulnerability. 5. Employ network segmentation to limit lateral movement if an endpoint is compromised. 6. Use Microsoft Defender for Office 365 and other email filtering solutions to block malicious documents before reaching end users. 7. Regularly audit and harden local security policies to reduce the attack surface, including disabling unnecessary macros and scripting features in Office applications. 8. Maintain up-to-date backups and incident response plans to quickly recover from potential exploitation.