VMware ESXi contains an authentication bypass vulnerability. A malicious actor with sufficient Active Directory (AD) permissions can gain full access to an ESXi host that was previously  configured to use AD for user management https://blogs.vmware.com/vsphere/2012/09/joining-vsphere-hosts-to-active-directory.html  by re-creating the configured AD group ('ESXi Admins' by default) after it was deleted from AD.