CVE-2024-21402 is a high-severity elevation of privilege vulnerability identified in Microsoft 365 Apps for Enterprise, specifically affecting Microsoft Outlook version 16.0.1. The vulnerability is categorized under CWE-285, which denotes improper authorization. This means that the application fails to correctly enforce access control policies, allowing an attacker with limited privileges to escalate their permissions within the affected environment. The CVSS 3.1 base score of 7.1 reflects a high severity level, with the vector indicating that the attack requires local access (AV:L), low attack complexity (AC:L), and privileges already present but limited (PR:L). No user interaction is required (UI:N), and the scope remains unchanged (S:U). The impact on confidentiality and integrity is high (C:H/I:H), while availability is not affected (A:N). The vulnerability does not currently have known exploits in the wild, but its presence in a widely used enterprise productivity suite makes it a significant concern. Improper authorization in Outlook could allow an attacker to gain elevated privileges, potentially enabling unauthorized access to sensitive emails, calendar data, or other corporate information, and possibly facilitating further lateral movement within an enterprise network. The lack of a published patch link suggests that remediation may still be pending or that updates are distributed through standard Microsoft update channels.

For European organizations, the impact of CVE-2024-21402 could be substantial due to the widespread adoption of Microsoft 365 Apps for Enterprise across various sectors including finance, government, healthcare, and critical infrastructure. An elevation of privilege vulnerability in Outlook could allow attackers to bypass security controls, access confidential communications, and manipulate or exfiltrate sensitive data. This could lead to data breaches, regulatory non-compliance (e.g., GDPR violations), reputational damage, and financial losses. Given that Outlook is often integrated with other Microsoft services and enterprise systems, exploitation could facilitate broader compromise within corporate networks. The high confidentiality and integrity impact means that sensitive personal and business information could be exposed or altered, undermining trust and operational security. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits once the vulnerability details become widely known.

European organizations should prioritize the following mitigation steps: 1) Verify and inventory all Microsoft 365 Apps for Enterprise installations, focusing on Outlook version 16.0.1 to identify vulnerable endpoints. 2) Apply the latest Microsoft security updates as soon as they become available, monitoring official Microsoft channels for patches addressing CVE-2024-21402. 3) Implement strict local access controls and limit user privileges to the minimum necessary, reducing the risk of local exploitation. 4) Enhance endpoint detection and response (EDR) capabilities to monitor for unusual privilege escalation activities, particularly on devices running the affected Outlook version. 5) Conduct targeted user awareness training emphasizing the risks of local privilege escalation and the importance of reporting suspicious behavior. 6) Employ application control policies to restrict execution of unauthorized code and scripts that could be used to exploit this vulnerability. 7) Review and tighten network segmentation to limit lateral movement opportunities if an endpoint is compromised. 8) Regularly audit and review access permissions within Microsoft 365 environments to detect and remediate any improper authorization configurations.