Hummingbird Collaboration (aka Hummingbird Enterprise Collaboration) 5.21 and earlier allows remote attackers to obtain sensitive information (intranet IP addresses and enumerations of valid parameter values) via a direct request to hc, which reveals the information in an error message or a cookie.
https://exchange.xforce.ibmcloud.com/vulnerabilities/24069
http://www.vupen.com/english/advisories/2006/0145
http://www.securityfocus.com/archive/1/421392/100/0/threaded