ZITADEL is an open source identity management platform. From 4.0.0 until 4.16.1, ZITADEL Login V2 creates a browser session after password verification and can reuse that session for a later authentication request without verifying a user's enrolled TOTP, OTP, or U2F second factor. When the MFA step is abandoned and login starts again, session-validity checks require MFA only when the organization enables Force MFA or Force MFA for local users only, so a voluntarily enrolled factor can be skipped while completing an OIDC or SAML callback for a customer application. Login V1, the ZITADEL Console, Management and Admin APIs, and user self-management are not affected. This issue is fixed in version 4.16.1.