VMware vCenter Server 5.5, 6.0, 6.5 allows vSphere users with certain, limited vSphere privileges to use the VIX API to access Guest Operating Systems without the need to authenticate.
The JMX RMI service in VMware vCenter Server 5.0 before u3e, 5.1 before u3b, 5.5 before u3, and 6.0 before u1 does not restrict registration of MBeans, which allows remote attackers to execute arbitrary code via the RMI protocol.