Due to a flaw in the handling of invalid ports, it is possible to cause the VMX process to fail. This vulnerability may allow a guest user to affect the VMX process resulting in a partial denial of service on the host.
Read VMware security advisory for ESXi 5.1 here – http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2062314