ZITADEL 3.x before 3.4.14 and 4.x before 4.16.2 contains an authentication bypass in the hosted Login V1 and Login V2 UIs that accepts passkey or other authenticator enrollment on identify-only login sessions, before any primary factor is verified. Unauthenticated attackers knowing only a victims login name can register an attacker-controlled authenticator and log in as that user, bypassing existing passwords and MFA.
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.