The web portal interface in Citrix Access Gateway (aka Citrix Advanced Access Control) before Advanced Edition 4.5 HF1 places a session ID in the URL, which allows context-dependent attackers to hijack sessions by reading "residual information", including the a referer log, browser history, or browser cache.
https://exchange.xforce.ibmcloud.com/vulnerabilities/35510
http://www.vupen.com/english/advisories/2007/2583
http://www.securityfocus.com/bid/24975
http://www.securityfocus.com/archive/1/482626/100/100/threaded
http://support.citrix.com/article/CTX113814
http://support.citrix.com/article/CTX112803
http://securitytracker.com/id?1018435