CVE-2025-54391 is a security vulnerability identified in the Zimbra Collaboration Suite (ZCS), specifically targeting the EnableTwoFactorAuthRequest SOAP endpoint. This vulnerability allows an attacker who already possesses valid user credentials to bypass the Two-Factor Authentication (2FA) mechanism that is intended to protect user accounts. The flaw lies in the ability of the attacker to configure an additional 2FA method—either by adding a third-party authenticator app or an email-based 2FA method—without needing to present a valid authentication token or demonstrate access to any previously configured 2FA method. Essentially, the attacker can manipulate the 2FA setup process to add a new 2FA factor under their control, thereby circumventing the existing 2FA protections. This results in unauthorized access to accounts that would otherwise be secured by 2FA, significantly undermining the security posture of affected Zimbra users. The vulnerability exploits the SOAP API endpoint responsible for managing 2FA configurations, indicating a design or implementation flaw in how authentication and authorization checks are enforced during 2FA setup. No specific affected versions have been disclosed, and no patches or exploits in the wild have been reported as of the publication date. The absence of a CVSS score suggests that the vulnerability is newly disclosed and pending further assessment.

For European organizations using Zimbra Collaboration Suite, this vulnerability poses a serious risk to account security and data confidentiality. Since Zimbra is widely used in enterprise and governmental email and collaboration environments, unauthorized access to user accounts could lead to data breaches, exposure of sensitive communications, and potential lateral movement within networks. The bypass of 2FA—a critical security control—means that attackers with stolen or otherwise obtained credentials can fully compromise accounts without additional hurdles, increasing the likelihood of successful account takeover attacks. This can result in loss of intellectual property, disruption of business operations, and damage to organizational reputation. Furthermore, compromised accounts could be leveraged to launch phishing campaigns, distribute malware, or exfiltrate data, amplifying the threat impact. The vulnerability's exploitation does not require advanced privileges beyond valid credentials, lowering the bar for attackers and increasing the threat surface. Given the importance of secure email and collaboration tools in European regulatory environments (e.g., GDPR), such breaches could also lead to regulatory penalties and compliance issues.

To mitigate this vulnerability, European organizations should prioritize the following actions: 1) Immediately monitor and audit all 2FA configuration changes within Zimbra environments to detect unauthorized modifications. 2) Restrict access to the EnableTwoFactorAuthRequest SOAP endpoint by implementing strict access controls, such as IP whitelisting, network segmentation, and limiting API access to trusted systems only. 3) Enforce strong credential hygiene policies, including regular password changes and detection of credential compromise, to reduce the risk of attackers obtaining valid credentials. 4) Deploy additional monitoring and anomaly detection tools to identify suspicious login patterns or unusual 2FA configuration activities. 5) Engage with Zimbra support or vendors to obtain patches or updates addressing this vulnerability as soon as they become available. 6) Consider implementing compensating controls such as conditional access policies or step-up authentication for sensitive operations. 7) Educate users about the importance of reporting unexpected 2FA prompts or changes. These measures go beyond generic advice by focusing on controlling and monitoring the specific vulnerable endpoint and the 2FA configuration process.