OpenSTAManager, an open source management software for technical assistance and invoicing, contains a critical privilege escalation and authentication bypass vulnerability in versions 2.9.8 and earlier. The vulnerability allows any attacker to arbitrarily change a user's group by directly calling modules/utenti/actions.php. Attackers can exploit this to promote existing accounts (such as agents) to the Amministratori (administrator) group or demote existing administrators. This represents a complete compromise of the application's access control system, allowing unauthorized elevation of privileges without authentication.