CVE-2024-21390 is a high-severity vulnerability identified in Microsoft Authenticator version 1.0.0, categorized under CWE-287 (Improper Authentication). This vulnerability allows an elevation of privilege attack vector, where an attacker can bypass or subvert the authentication mechanisms of the Microsoft Authenticator application. The CVSS 3.1 base score is 7.1, indicating a high impact with the vector string AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N. This means the attack requires local access (AV:L), low attack complexity (AC:L), no privileges required (PR:N), but user interaction is necessary (UI:R). The scope remains unchanged (S:U), and the impact on confidentiality and integrity is high (C:H/I:H), while availability is not affected (A:N). The vulnerability essentially allows an attacker with local access and the ability to trick the user into interaction to gain elevated privileges within the Microsoft Authenticator app, potentially compromising sensitive authentication tokens or credentials. Since Microsoft Authenticator is widely used for multi-factor authentication (MFA) to secure access to Microsoft accounts and enterprise resources, exploitation could undermine the security of MFA-protected accounts, leading to unauthorized access and potential lateral movement within networks. No known exploits are currently reported in the wild, and no patches are linked yet, indicating that mitigation may rely on vendor updates and user awareness for now.

For European organizations, the impact of this vulnerability is significant due to the widespread adoption of Microsoft Authenticator as a primary MFA tool in corporate environments. Successful exploitation could lead to unauthorized access to critical systems, data breaches involving personal and business data, and potential compliance violations under GDPR due to compromised authentication mechanisms. The elevation of privilege could allow attackers to impersonate legitimate users, bypassing MFA protections and gaining access to sensitive applications, cloud services, and internal networks. This risk is heightened in sectors with stringent security requirements such as finance, healthcare, and government institutions. The local attack vector implies that attackers need some level of physical or local device access, which could be feasible in scenarios involving lost or stolen devices or insider threats. The requirement for user interaction suggests phishing or social engineering could be used to trigger the exploit, increasing the attack surface. Overall, the vulnerability threatens confidentiality and integrity of authentication processes, potentially leading to severe operational and reputational damage for European organizations relying on Microsoft Authenticator.

To mitigate this vulnerability, European organizations should: 1) Immediately verify the version of Microsoft Authenticator deployed and restrict usage of version 1.0.0 until a vendor patch is released. 2) Implement strict device management policies including encryption, remote wipe capabilities, and endpoint detection to reduce risk from lost or stolen devices. 3) Educate users about the risks of social engineering and phishing attacks that could trigger the required user interaction for exploitation. 4) Employ additional layers of security such as conditional access policies that limit authentication attempts from untrusted devices or locations. 5) Monitor authentication logs for unusual patterns that may indicate exploitation attempts. 6) Coordinate with Microsoft for timely updates and apply patches as soon as they become available. 7) Consider temporary alternative MFA solutions or hardware tokens for high-risk users until the vulnerability is remediated. 8) Conduct regular security audits and penetration testing focused on authentication mechanisms to detect potential weaknesses.