An authentication flaw in Zimbra Collaboration permits users with valid credentials to bypass Two-Factor Authentication, significantly increasing the risk of account takeover.

This vulnerability resides in the EnableTwoFactorAuthRequest SOAP endpoint. While it requires valid user credentials, it allows an authenticated attacker to circumvent the 2FA layer, effectively neutralizing the multi-factor security control.

By bypassing 2FA, an attacker who has obtained valid credentials can maintain persistent access to an account, even if the organization has mandated MFA. This increases the risk of data theft, lateral movement, and unauthorized access to sensitive communications, justifying the critical 9.1 CVSS score.

Immediate Action: Apply the vendor-supplied patch or update to the latest version of Zimbra Collaboration as specified in the official vendor security advisory.

Proactive Monitoring: Audit recent authentication logs for suspicious patterns, particularly where 2FA might have been bypassed or disabled unexpectedly.

Compensating Controls: Implement stricter API rate limiting and monitor SOAP endpoint traffic for anomalous requests originating from suspicious internal or external IP addresses.

Public Exploit Available: Unknown

MFA is a primary defense against credential-based attacks; the ability to bypass this control renders standard security policies ineffective. It is imperative that administrators verify their current ZCS version against the vendor's patch release notes and apply the necessary updates immediately to restore the integrity of the 2FA system.