| V-256453 | medium | Virtual disk shrinking must be disabled on the virtual machine (VM). | 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 (those 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 nonadministrative users operating within the VM's guest operating system. |
| V-256454 | medium | Virtual disk wiping must be disabled on the virtual machine (VM). | 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 (those 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 nonadministrative users operating within the VM's guest operating system. |
| V-256455 | medium | Independent, nonpersistent disks must not be used on the virtual machine (VM). | The security issue with nonpersistent disk mode is that successful attackers, with a simple shutdown or reboot, might undo or remove any traces they were ever on the machine. To safeguard against this risk, production virtual machines should be set to use persistent disk mode; additionally, ensure 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. |
| V-256456 | medium | Host Guest File System (HGFS) file transfers must be disabled on the virtual machine (VM). | Setting "isolation.tools.hgfsServerSet.disable" to "true" disables registration of the guest's HGFS server with the host. Application Programming Interfaces (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 use this to transfer files inside the guest operating system. |
| V-256457 | medium | Unauthorized floppy devices must be disconnected on the virtual machine (VM). | Ensure 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 data center environment, and CD/DVD drives are usually connected only temporarily during software installation. |
| V-256459 | medium | Unauthorized parallel devices must be disconnected on the virtual machine (VM). | Ensure 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 data center environment, and CD/DVD drives are usually connected only temporarily during software installation. |
| V-256460 | medium | Unauthorized serial devices must be disconnected on the virtual machine (VM). | Ensure 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. |
| V-256461 | medium | Unauthorized USB devices must be disconnected on the virtual machine (VM). | Ensure 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 data center environment, and CD/DVD drives are usually connected only temporarily during software installation. |
| V-256462 | medium | Console connection sharing must be limited on the virtual machine (VM). | By default, more than one user at a time can connect to remote console sessions. When multiple sessions are activated, each terminal window receives a notification about the new session. If an administrator in the VM logs in using a VMware remote console during their session, a nonadministrator 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 VM. For example, if a jump box is being used for an open console session and the administrator loses connection to that box, the console session remains open. Allowing two console sessions permits debugging via a shared session. For the highest security, allow only one remote console session at a time. |
| V-256464 | medium | Unauthorized removal, connection, and modification of devices must be prevented on the virtual machine (VM). | 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. To use the device again, 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. |
| V-256465 | medium | The virtual machine (VM) must not be able to obtain host information from the hypervisor. | 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 could use this information to inform further attacks on the host. |
| V-256469 | medium | Use of the virtual machine (VM) console must be minimized. | 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 could allow a malicious user to bring down a VM. In addition, it impacts performance on the service console, especially if many VM console sessions are open simultaneously. |
| V-256470 | medium | The virtual machine (VM) guest operating system must be locked when the last console connection is closed. | When accessing the VM console, the guest operating system 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. |
| V-256472 | medium | Encryption must be enabled for vMotion on the virtual machine (VM). | 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 256-bit AES-GCM with negligible performance impact.
vSphere 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 hosts, encryption will always be used. However, because 6.0 and earlier releases do not support this feature, vMotion from a 7.0 host to a 6.0 host would be allowed but would not be encrypted. If the encryption is set to "Required", vMotions to unsupported hosts will fail. This must be set to "Opportunistic" or "Required". |
| V-256473 | medium | Logging must be enabled on the virtual machine (VM). | The ESXi hypervisor maintains logs for each individual VM by default. These logs contain information including but not limited to power events, system failure information, tools status and activity, time sync, virtual hardware changes, vMotion migrations and machine clones. Due to the value these logs provide for the continued availability of each VM and potential security incidents, these logs must be enabled. |
| V-256474 | medium | Log size must be configured properly on the virtual machine (VM). | The ESXi hypervisor maintains logs for each individual VM by default. These logs contain information including but not limited to power events, system failure information, tools status and activity, time sync, virtual hardware changes, vMotion migrations, and machine clones.
By default, the size of these logs is unlimited, and they are only rotated on vMotion or power events. This can cause storage issues at scale for VMs that do not vMotion or power cycle often. |
| V-256475 | medium | Log retention must be configured properly on the virtual machine (VM). | The ESXi hypervisor maintains logs for each individual VM by default. These logs contain information including but not limited to power events, system failure information, tools status and activity, time sync, virtual hardware changes, vMotion migrations, and machine clones.
By default, 10 of these logs are retained. This is normally sufficient for most environments, but this configuration must be verified and maintained. |
| V-256476 | medium | DirectPath I/O must be disabled on the virtual machine (VM) when not required. | VMDirectPath I/O (PCI passthrough) enables direct assignment of hardware PCI functions to VMs. This gives the VM access to the PCI functions with minimal intervention from the ESXi host. This is a powerful feature for legitimate applications such as virtualized storage appliances, backup appliances, dedicated graphics, etc., but it also allows a potential attacker highly privileged access to underlying hardware and the PCI bus. |
| V-256477 | medium | Encryption must be enabled for Fault Tolerance on the virtual machine (VM). | Fault Tolerance log traffic can be encrypted. This could contain sensitive data from the protected machine's memory or CPU instructions.
vSphere Fault Tolerance performs frequent checks between a primary VM and secondary VM so the secondary VM can quickly resume from the last successful checkpoint. The checkpoint contains the VM state that has been modified since the previous checkpoint.
When Fault Tolerance is turned on, FT encryption is set to "Opportunistic" by default, which means it enables encryption only if both the primary and secondary host are capable of encryption. |
| V-256450 | low | Copy operations must be disabled on the virtual machine (VM). | Copy and paste operations are disabled by default; however, explicitly disabling this feature will enable audit controls to verify this setting is correct. Copy, paste, drag and drop, or GUI copy/paste operations between the guest operating system and the remote console could provide the means for an attacker to compromise the VM. |
| V-256451 | low | Drag and drop operations must be disabled on the virtual machine (VM). | Copy and paste operations are disabled by default; however, explicitly disabling this feature will enable audit controls to verify this setting is correct. Copy, paste, drag and drop, or GUI copy/paste operations between the guest operating system and the remote console could provide the means for an attacker to compromise the VM. |
| V-256452 | low | Paste operations must be disabled on the virtual machine (VM). | Copy and paste operations are disabled by default; however, explicitly disabling this feature will enable audit controls to verify this setting is correct. Copy, paste, drag and drop, or GUI copy/paste operations between the guest operating system and the remote console could provide the means for an attacker to compromise the VM. |
| V-256458 | low | Unauthorized CD/DVD devices must be disconnected on the virtual machine (VM). | Ensure 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 data center environment, and CD/DVD drives are usually connected only temporarily during software installation. |
| V-256463 | low | Informational messages from the virtual machine to the VMX file must be limited on the virtual machine (VM). | The configuration file containing these name-value pairs is limited to a size of 1MB. If not limited, VMware tools in the guest operating system are capable of sending a large and continuous data stream to the host. This 1MB capacity should be sufficient for most cases, but this value can change if necessary.
The value can be increased if large amounts of custom information are being stored in the configuration file. The default limit is 1MB. |
| V-256466 | low | Shared salt values must be disabled on the virtual machine (VM). | When salting is enabled (Mem.ShareForceSalting=1 or 2) to share a page between two virtual machines, both salt and the content of the page must be same. A salt value is a configurable advanced option for each virtual machine. The salt values can be specified manually in the virtual machine's advanced settings with the new option "sched.mem.pshare.salt".
If this option is not present in the virtual machine's advanced settings, the value of the "vc.uuid" option is taken as the default value. Because the "vc.uuid" is unique to each virtual machine, by default Transparent Page Sharing (TPS) happens only among the pages belonging to a particular virtual machine (Intra-VM). |
| V-256467 | low | Access to virtual machines (VMs) through the "dvfilter" network Application Programming Interface (API) must be controlled. | An attacker might compromise a VM by using the "dvFilter" API. Configure only VMs that need this access to use the API. |
| V-256468 | low | System administrators must use templates to deploy virtual machines (VMs) whenever possible. | Capture a hardened base operating system image (with no applications installed) in a template to ensure all VMs are created with a known baseline level of security. Use this template to create other, application-specific templates, or use the application template to deploy VMs. Manual installation of the operating system and applications into a VM introduces the risk of misconfiguration due to human or process error. |
| V-256471 | low | All 3D features on the virtual machine (VM) must be disabled when not required. | For performance reasons, it is recommended that 3D acceleration be disabled on virtual machines that do not require 3D functionality (e.g., most server workloads or desktops not using 3D applications). |