CVE-2025-21395 is a high-severity heap-based buffer overflow vulnerability (CWE-122) found in Microsoft Office 2019, specifically affecting Microsoft Access. The vulnerability allows remote code execution (RCE) when a user opens a specially crafted Access file. The flaw arises due to improper handling of memory buffers on the heap, which can be exploited by an attacker to overwrite memory, potentially leading to arbitrary code execution with the privileges of the current user. The CVSS 3.1 base score of 7.8 reflects a high impact, with an attack vector of local (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 reported in the wild, the vulnerability is critical enough to warrant immediate attention. The lack of available patches at the time of publication increases the risk window. This vulnerability could be leveraged by attackers to execute arbitrary code, install malware, or gain persistent access to affected systems through malicious Access database files delivered via phishing or other social engineering methods.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Microsoft Office 2019, including Microsoft Access, in enterprise environments. Successful exploitation could lead to unauthorized access, data breaches, and disruption of business operations. Confidentiality could be compromised through data exfiltration, integrity through unauthorized modification of data, and availability through potential system crashes or ransomware deployment. Sectors such as finance, healthcare, government, and critical infrastructure, which rely heavily on Microsoft Office products, could face severe operational and reputational damage. The requirement for user interaction means that phishing campaigns targeting European users could be an effective attack vector, increasing the risk of exploitation. The absence of known exploits currently provides a window for proactive mitigation, but also means organizations must be vigilant for emerging threats.

European organizations should implement a multi-layered mitigation strategy. First, apply any available security updates or patches from Microsoft immediately once released. Until patches are available, restrict or monitor the use of Microsoft Access files from untrusted sources. Employ advanced email filtering and anti-phishing solutions to reduce the likelihood of malicious Access files reaching end users. Implement application whitelisting to prevent unauthorized execution of malicious code. Educate users about the risks of opening unexpected or suspicious Office documents, emphasizing caution with Access files. Utilize endpoint detection and response (EDR) tools to detect anomalous behavior indicative of exploitation attempts. Network segmentation can limit lateral movement if a system is compromised. Finally, maintain regular backups and test restoration procedures to mitigate the impact of potential ransomware or data corruption resulting from exploitation.