core: REDAXO before 5.21.3 CSRF Token Bypass via users/users Privilege Escalation

REDAXO before 5.21.3 contains a cross-site request forgery vulnerability in the backend user administration page (users/users) because the CSRF token check only runs when the save parameter is set, while the update path triggered by FUNC_UPDATE does not require it. Attackers can lure a logged-in backend user with the users[] permission to a crafted GET link to grant administrator rights, deactivate accounts, or lock out the sole administrator.