A flaw was found in the Keycloak Organization identity-first login flow. The vulnerability is caused by a failure to clear the SSO re-authentication flag (SSO_AUTH note) when a flow transition occurs, such as moving to the reset-credentials or registration path, even though the authenticated user is removed from the authentication session. An attacker with valid credentials in two or more organizations can exploit this by initiating an organization-scoped authorization request, triggering a flow transition, and then submitting a victim's username. The Organization authenticator incorrectly trusts the stale re-authentication flag as valid proof of identity for the new username. Successful exploitation allows a remote attacker with Low privileges to perform a full account takeover, obtaining the victim's authorization code, access tokens, and a valid SSO session usable against downstream applications.