VMware vCenter and ESXi updates address critical security issues
VMware vCenter Server contains a remotely accessible JMX RMI service that is not securely configured. An unauthenticated remote attacker that is able to connect to the service may be able use it to execute arbitrary code on the vCenter server.
VMware vCenter Server does not properly sanitize long heartbeat messages. Exploitation of this issue may allow an unauthenticated attacker to create a denial-of-service condition in the vpxd service.
To find out which versions are affected read VMware’s Security Advisory here - http://www.vmware.com/security/advisories/VMSA-2015-0007.html