Zitadel Bypass Second Authentication Factor

Starting from 2.53.6, 2.54.3, and 2.55.0, Zitadel only required multi factor authentication in case the login policy has either enabled requireMFA or requireMFAForLocalUsers. If a user has set up MFA without this requirement, Zitadel would consider single factor auhtenticated sessions as valid as well and not require multiple factors. Bypassing second authentication factors weakens multifactor authentication and enables attackers to bypass the more secure factor. An attacker can target the TOTP code alone, only six digits, bypassing password verification entirely and potentially compromising accounts with 2FA enabled. This vulnerability is fixed in 4.6.0, 3.4.3, and 2.71.18.