Cisco WebEx Training Center allows remote attackers to discover registration IDs via a crafted URL, aka Bug ID CSCul57121.
https://exchange.xforce.ibmcloud.com/vulnerabilities/89651
http://www.securitytracker.com/id/1029492
http://www.securityfocus.com/bid/64286
http://tools.cisco.com/security/center/viewAlert.x?alertId=32144
http://tools.cisco.com/security/center/content/CiscoSecurityNotice/CVE-2013-6973