Citrix XenServer 4.1, 6.0, 5.6 SP2, 5.6 Feature Pack 1, 5.6 Common Criteria, 5.6, 5.5, 5.0, and 5.0 Update 3 contains a Local Privilege Escalation Vulnerability which could allow local users with access to a guest operating system to gain elevated privileges.

Citrix XenServer 5.0 Update 2 and earlier, and 5.5 Update 1 and earlier, when using a pvops kernel, allows guest users to cause a denial of service in the host via unspecified vectors that trigger "incorrectly set flags."