GHSA-hf67-5vvq-fm3r Keycloak: Session fixation in OIDC login flow that can lead to account takeover

• Maven org.keycloak:keycloak-services: < 26.6.2 → fixed in 26.6.2

A session fixation vulnerability was found in Keycloak's login-actions endpoints. An unauthenticated attacker could exploit this flaw by pre-creating an authentication session and tricking a victim into visiting a maliciously crafted link. By leveraging the /login-actions/restart endpoint—which processes session handles without adequate CSRF protection or cookie ownership validation—an attacker can reset the authentication flow state. This causes Single Sign-On (SSO) to authenticate the victim transparently upon clicking the link, allowing the attacker to hijack the required-action form without needing the victim's credentials. A successful exploit could lead to complete account takeover, including highly privileged administrative accounts.