VMware vSphere 6.5 Virtual Machine Security Technical Implementation Guide

Shrinking a virtual disk reclaims unused space in it. If there is empty space in the disk, this process reduces the amount of space the virtual disk occupies on the host drive. Normal users and processes-that is, users and processes without root or administrator privileges-within virtual machines have the capability to invoke this procedure. However, if this is done repeatedly, the virtual disk can become unavailable while this shrinking is being performed, effectively causing a denial-of-service. In most datacenter environments, disk shrinking is not done, so this feature must be disabled. Repeated disk shrinking can make a virtual disk unavailable. The capability to shrink is available to non-administrative users operating within the VMs guest OS.

Shrinking and wiping (erasing) a virtual disk reclaims unused space in it. If there is empty space in the disk, this process reduces the amount of space the virtual disk occupies on the host drive. Normal users and processes - that is, users and processes without root or administrator privileges - within virtual machines have the capability to invoke this procedure. However, if this is done repeatedly, the virtual disk can become unavailable while this shrinking is being performed, effectively causing a denial-of-service. In most datacenter environments, disk shrinking is not done, so this feature must be disabled. Repeated disk shrinking can make a virtual disk unavailable. The capability to wipe (erase) is available to non-administrative users operating within the VMs guest OS.

The security issue with nonpersistent disk mode is that successful attackers, with a simple shutdown or reboot, might undo or remove any traces that they were ever on the machine. To safeguard against this risk, production virtual machines should be set to use persistent disk mode; additionally, make sure that activity within the VM is logged remotely on a separate server, such as a syslog server or equivalent Windows-based event collector. Without a persistent record of activity on a VM, administrators might never know whether they have been attacked or hacked. There can be valid use cases for these types of disks such as with an application presentation solution where read only disks are desired and such cases should be identified and documented.

Setting isolation.tools.hgfsServerSet.disable to true disables registration of the guest's HGFS server with the host. APIs that use HGFS to transfer files to and from the guest operating system, such as some VIX commands, will not function. An attacker could potentially use this to transfer files inside the guest OS.

Ensure that no device is connected to a virtual machine if it is not required. For example, floppy, serial and parallel ports are rarely used for virtual machines in a datacenter environment, and CD/DVD drives are usually connected only temporarily during software installation.

Ensure that no device is connected to a virtual machine if it is not required. For example, floppy, serial and parallel ports are rarely used for virtual machines in a datacenter environment, and CD/DVD drives are usually connected only temporarily during software installation.

Ensure that no device is connected to a virtual machine if it is not required. For example, floppy, serial and parallel ports are rarely used for virtual machines in a datacenter environment, and CD/DVD drives are usually connected only temporarily during software installation.

Ensure that no device is connected to a virtual machine if it is not required. For example, floppy, serial and parallel ports are rarely used for virtual machines in a datacenter environment, and CD/DVD drives are usually connected only temporarily during software installation.

By default, remote console sessions can be connected to by more than one user at a time. When multiple sessions are activated, each terminal window gets a notification about the new session. If an administrator in the VM logs in using a VMware remote console during their session, a non-administrator in the VM might connect to the console and observe the administrator's actions. Also, this could result in an administrator losing console access to a virtual machine. For example, if a jump box is being used for an open console session and the admin loses connection to that box, then the console session remains open. Allowing two console sessions permits debugging via a shared session. For highest security, only one remote console session at a time should be allowed.

The VM console enables you to connect to the console of a virtual machine, in effect seeing what a monitor on a physical server would show. This console is also available via the VNC protocol and should be disabled.

In a virtual machine, users and processes without root or administrator privileges can connect or disconnect devices, such as network adaptors and CD-ROM drives, and can modify device settings. Use the virtual machine settings editor or configuration editor to remove unneeded or unused hardware devices. If you want to use the device again, you can prevent a user or running process in the virtual machine from connecting, disconnecting, or modifying a device from within the guest operating system. By default, a rogue user with nonadministrator privileges in a virtual machine can: 1. Connect a disconnected CD-ROM drive and access sensitive information on the media left in the drive 2. Disconnect a network adaptor to isolate the virtual machine from its network, which is a denial of service 3. Modify settings on a device

If enabled, a VM can obtain detailed information about the physical host. The default value for the parameter is FALSE. This setting should not be TRUE unless a particular VM requires this information for performance monitoring. An adversary potentially can use this information to inform further attacks on the host.

The VM console enables a connection to the console of a virtual machine, in effect seeing what a monitor on a physical server would show. The VM console also provides power management and removable device connectivity controls, which might potentially allow a malicious user to bring down a virtual machine. In addition, it also has a performance impact on the service console, especially if many VM console sessions are open simultaneously.

When accessing the VM console the guest OS must be locked when the last console user disconnects, limiting the possibility of session hijacking. This setting only applies to Windows-based VMs with VMware tools installed.

vMotion migrations in vSphere 6.0 and earlier transferred working memory and CPU state information in clear text over the vMotion network. As of vSphere 6.5 this transfer can be transparently encrypted using 256bit AES-GCM with negligible performance impact. vSphere 6.5 enables encrypted vMotion by default as 'Opportunistic', meaning that encrypted channels are used where supported but the operation will continue in plain text where encryption is not supported. For example when vMotioning between two 6.5 hosts encryption will always be utilized but since 6.0 and earlier releases do not support this feature vMotion from a 6.5 host to a 6.0 host would be allowed but would not be encrypted. If this finding is set to 'Required' then vMotions to unsupported hosts will fail. This setting must be set to 'Opportunistic' or 'Required'.