The Session Reliability Service (XTE) in Citrix MetaFrame Presentation Server 3.0, Presentation Server 4.0, and Access Essentials 1.0 and 1.5, allows remote attackers to bypass network security policies and connect to arbitrary TCP ports via a modified address:port string.
https://exchange.xforce.ibmcloud.com/vulnerabilities/34448
http://www.vupen.com/english/advisories/2007/1918
http://www.securitytracker.com/id?1018098
http://support.citrix.com/article/CTX112964
http://secunia.com/advisories/25371
http://fortconsult.net/files/fortconsult.dk/citrix_advisory.pdf