CVE-2025-21366 is a high-severity use-after-free vulnerability (CWE-416) affecting Microsoft Office 2019, specifically within Microsoft Access. This vulnerability allows remote code execution (RCE) when a user opens a specially crafted Access file. The flaw arises because the software improperly handles memory, freeing an object and then continuing to use it, which can lead to arbitrary code execution by an attacker. The CVSS 3.1 base score of 7.8 reflects a high impact, with the vector indicating local attack vector (AV:L), low attack complexity (AC:L), no privileges required (PR:N), but requiring user interaction (UI:R). The scope is unchanged (S:U), and the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). Although no known exploits are currently in the wild and no patches have been linked yet, the vulnerability poses a significant risk because it can be triggered by opening a malicious file, a common attack vector in enterprise environments. The vulnerability is present in version 19.0.0 of Microsoft Office 2019, which remains widely used in many organizations. The lack of a patch at the time of publication increases the urgency for mitigation and monitoring.

For European organizations, this vulnerability presents a substantial risk due to the widespread use of Microsoft Office 2019 across various sectors including government, finance, healthcare, and critical infrastructure. Successful exploitation could lead to full system compromise, data breaches, and disruption of business operations. Given the high confidentiality, integrity, and availability impacts, attackers could exfiltrate sensitive data, alter or destroy critical information, or deploy ransomware or other malware. The requirement for user interaction means phishing or social engineering campaigns could be leveraged to deliver malicious Access files. The local attack vector suggests that initial access is needed on the victim machine, but since no privileges are required, any user opening the malicious file is at risk. This vulnerability could be particularly damaging in environments where Access databases are used for sensitive data processing or where endpoint security is insufficient. The absence of known exploits in the wild currently provides a window for proactive defense, but the potential for rapid weaponization remains.

European organizations should immediately implement the following specific mitigations: 1) Restrict or disable Microsoft Access usage where not necessary, especially in high-risk user groups. 2) Employ application whitelisting and endpoint protection solutions that can detect and block suspicious Access database files or abnormal Access process behavior. 3) Educate users about the risks of opening unsolicited or unexpected Access files, emphasizing phishing awareness and safe handling of email attachments. 4) Monitor network and endpoint logs for unusual activity related to Access or Office applications. 5) Apply principle of least privilege to limit user permissions, reducing the impact of potential exploitation. 6) Prepare for rapid deployment of patches once Microsoft releases an official fix, including testing and validation in controlled environments. 7) Consider network segmentation to isolate systems that handle sensitive Access databases from general user workstations. 8) Use advanced threat detection tools capable of identifying use-after-free exploitation techniques. These measures go beyond generic advice by focusing on Access-specific controls and user behavior adjustments.