CVE-2025-26629 is a high-severity use-after-free vulnerability (CWE-416) found in Microsoft 365 Apps for Enterprise, specifically version 16.0.1. This vulnerability arises when the application improperly manages memory, allowing an attacker to exploit a freed memory region. An unauthorized attacker can leverage this flaw to execute arbitrary code locally on the affected system. The vulnerability requires local access and user interaction to trigger, as indicated by the CVSS vector (AV:L/UI:R). The flaw impacts confidentiality, integrity, and availability, as successful exploitation can lead to full system compromise, including the execution of malicious code with the privileges of the logged-in user. Although no known exploits are currently reported in the wild, the vulnerability's characteristics and the widespread use of Microsoft 365 Apps for Enterprise make it a significant risk. The vulnerability was publicly disclosed on March 11, 2025, and no official patches have been linked yet, emphasizing the need for immediate attention and mitigation by affected organizations.

For European organizations, this vulnerability poses a substantial risk due to the extensive adoption of Microsoft 365 Apps for Enterprise across various sectors including government, finance, healthcare, and critical infrastructure. Exploitation could lead to unauthorized code execution, data breaches, disruption of business operations, and potential lateral movement within corporate networks. Given the high confidentiality, integrity, and availability impact, organizations could face regulatory repercussions under GDPR if sensitive personal data is compromised. The requirement for local access and user interaction means phishing or social engineering campaigns could be used to facilitate exploitation, increasing the threat surface. Additionally, the lack of a patch at the time of disclosure heightens the urgency for organizations to implement interim mitigations to protect their environments.

1. Implement strict endpoint security controls including application whitelisting and behavior-based detection to identify and block suspicious activities related to Microsoft 365 Apps. 2. Educate users on phishing and social engineering tactics to reduce the likelihood of triggering the vulnerability via malicious documents or links. 3. Employ network segmentation to limit the spread of potential compromise from affected endpoints. 4. Monitor logs and endpoint telemetry for unusual behaviors indicative of exploitation attempts, such as unexpected process creations or memory access violations. 5. Apply principle of least privilege to user accounts to minimize the impact of code execution under compromised credentials. 6. Regularly check for and apply official patches or updates from Microsoft as soon as they become available. 7. Use advanced threat protection solutions that can sandbox and analyze suspicious documents before they reach end users. 8. Temporarily restrict or disable features in Microsoft 365 Apps that are not essential and could be vectors for exploitation until a patch is released.