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CVE-2026-105211 – Authentication Bypass / Account Takeover – ZITADEL 4.0.0–4.17.0

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Summary

CVE-2026-105211 is an authentication bypass vulnerability in ZITADEL’s Login V2 UI that allows an unauthenticated attacker who knows only a victim’s login name to obtain a fully MFA-authenticated session. The flaw stems from the returnCode OTP delivery type returning one-time passcodes directly in the HTTP response instead of sending them out-of-band, letting the attacker complete both OTP factors without any credentials. Exploitation can lead to full account takeover, including compromise of administrator accounts and the underlying ZITADEL instance.

Technical details

  • Root cause: the Login V2 server-side flow exposes the returnCode OTP delivery type, which returns the generated OTP code directly in the server response rather than delivering it only to the victim’s email or phone.
  • Trigger conditions: the targeted account must have both OTP-Email and OTP-SMS registered as second factors; the attacker needs only the victim’s login name/username.
  • Attack vector: network-accessible, no prior authentication or user interaction required; the attacker submits an identify-only session, requests OTP challenges via returnCode for both email and SMS factors, reads both codes from the responses, and submits them.
  • Impact: the backend’s MFA evaluation logic accepts two second factors as sufficient authentication, producing a session ZITADEL treats as MFA-authenticated without any primary factor (password, passkey, or IdP) ever being verified — resulting in account takeover and, for privileged accounts, full instance compromise.

Affected software

  • ZITADEL 4.x versions 4.0.0 through 4.17.0 (including release candidates in that range)

Severity

  • CVSS v4.0 Base Score: 9.2 (Critical) — CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
  • CVSS v3.1 Base Score (as also published): 8.1 (High) — CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade ZITADEL to version 4.17.1 or later, which prevents the browser from requesting OTP codes via returnCode in the Login V2 flow.
  • If upgrading is not immediately possible: avoid enrolling both OTP-Email and OTP-SMS on the same account, particularly for privileged/administrative users, and prefer TOTP, U2F/security keys, or passkeys as second factors instead.

References

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