Keycloak: stale login flag lets attacker take over victim accounts

A flaw was found in the Organization identity-first login flow of the Keycloak authentication server. Keycloak is an open-source identity and access management solution used to secure modern applications and services. The issue occurs when an attacker who belongs to multiple organizations initiates a login and then switches to a registration or password reset path. During this process, a flag indicating a successful login is not properly cleared when the user is removed from the session. An attacker can then provide a victim's username, and the system incorrectly treats the stale flag as proof of the victim's identity. This allows the attacker to bypass authentication and gain full access to the victim's account and connected applications.