The UltimateAI plugin for WordPress is vulnerable to authentication bypass in all versions up to, and including, 2.8.3. This is due to the improper empty value check and a missing default activated value check in the 'ultimate_ai_change_pass' function. This makes it possible for unauthenticated attackers to reset the password of the first user, whose account is not yet activated or the first user who activated their account, who are subscribers.