To protect the host against unauthorized intrusion and misuse, VMware imposes constraints on several parameters, settings, and activities. You can loosen the constraints to meet your configuration needs. If you do, make sure that you are working in a trusted environment and that you have taken enough other security measures to protect the network as a whole and the devices connected to the host.
Consider the following recommendations when evaluating host security and administration.
Limit user access.
To improve security, restrict user access to the Direct Console User Interface (DCUI) and the ESXi Shell and enforce access security policies, for example, by setting up password restrictions.
The ESXi Shell has privileged access to certain parts of the host. Provide only trusted users with ESXi Shell login access.
Use the vSphere Client to administer standalone ESXi hosts.
Whenever possible, use the vSphere Client or a third-party network management tool to administer your ESXi hosts instead of working though the command-line interface as the root user. Using the vSphere Client lets you limit the accounts with access to the ESXi Shell, safely delegate responsibilities, and set up roles that prevent administrators and users from using capabilities they do not need.
Use the vSphere Web Client to administer ESXi hosts that are managed by a vCenter Server. Do not access managed hosts directly with the vSphere Client, and do not make changes to managed hosts from the host's DCUI.
Use only VMware sources to upgrade ESXi components.
The host runs a variety of third-party packages to support management interfaces or tasks that you must perform. VMware does not support upgrading these packages from anything other than a VMware source. If you use a download or patch from another source, you might compromise management interface security or functions. Regularly check third-party vendor sites and the VMware knowledge base for security alerts.
In addition to implementing the firewall, risks to the hosts are mitigated using other methods.
ESXi runs only services essential to managing its functions, and the distribution is limited to the features required to run ESXi.
By default, all ports not specifically required for management access to the host are closed. You must specifically open ports if you need additional services.
By default, weak ciphers are disabled and all communications from clients are secured by SSL. The exact algorithms used for securing the channel depend on the SSL handshake. Default certificates created on ESXi use PKCS#1 SHA-256 With RSA encryption as the signature algorithm.
The Tomcat Web service, used internally by ESXi to support access by Web clients, has been modified to run only those functions required for administration and monitoring by a Web client. As a result, ESXi is not vulnerable to the Tomcat security issues reported in broader use.
VMware monitors all security alerts that could affect ESXi security and issues a security patch if needed.
Insecure services such as FTP and Telnet are not installed, and the ports for these services are closed by default. Because more secure services such as SSH and SFTP are easily available, always avoid using these insecure services in favor of their safer alternatives. For example, use Telnet with SSL instead of Telnet to access virtual serial ports. If you must use insecure services and have implemented sufficient protection for the host, you must explicitly open ports to support them.
Follow the VMware security advisories at http://www.vmware.com/security/.