A vulnerability in web interface of the Cisco Webex Event Center, Cisco Webex Meeting Center, Cisco Webex Support Center, and Cisco Webex Training Center could allow an unauthenticated, remote attacker to guess account usernames. The vulnerability is due to missing CAPTCHA protection in certain URLs. An attacker could exploit this vulnerability by sending a crafted request to the web interface. A successful exploit could allow the attacker to know if a given username is valid and find the real name of the user.