A vulnerability in the auto discovery phase of Cisco Spark Hybrid Calendar Service could allow an unauthenticated, remote attacker to view sensitive information in the unencrypted headers of an HTTP method request. The attacker could use this information to conduct additional reconnaissance attacks leading to the disclosure of sensitive customer data. The vulnerability exists in the auto discovery phase because an unencrypted HTTP request is made due to requirements for implementing the Hybrid Calendar service. An attacker could exploit this vulnerability by monitoring the unencrypted traffic on the network. An exploit could allow the attacker to access sensitive customer data belonging to Office365 users, such as email and calendar events. Cisco Bug IDs: CSCvg35593.