Citrix MetaFrame up to XP 1.0 Feature 1, except when running on Windows Server 2003, installs a registry key with an insecure ACL, which allows remote authenticated users to gain privileges.
http://www.vupen.com/english/advisories/2006/2862
http://www.securityfocus.com/bid/19056
http://support.citrix.com/article/CTX110492