7.1.5. RDP authentication
For each virtual machine that is remotely accessible via RDP, you can individually determine if and how client connections are authenticated. For this, use VBoxManage modifyvm command with the --vrdeauthtype option; see Section 8.8, “VBoxManage modifyvm” for a general introduction. Three methods of authentication are available:
The "null" method means that there is no authentication at all; any client can connect to the VRDP server and thus the virtual machine. This is, of course, very insecure and only to be recommended for private networks.
The "external" method provides external authentication through a special authentication library. VirtualBox ships with two such authentication libraries:
The default authentication library, VBoxAuth, authenticates against user credentials of the hosts. Depending on the host platform, this means:
On Linux hosts, VBoxAuth.so authenticates users against the host's PAM system.
On Windows hosts, VBoxAuth.dll authenticates users against the host's WinLogon system.
On Mac OS X hosts, VBoxAuth.dylib authenticates users against the host's directory service.[35]
In other words, the "external" method per default performs authentication with the user accounts that exist on the host system. Any user with valid authentication credentials is accepted, i.e. the username does not have to correspond to the user running the VM.
An additional library called VBoxAuthSimple performs authentication against credentials configured in the "extradata" section of a virtual machine's XML settings file. This is probably the simplest way to get authentication that does not depend on a running and supported guest (see below). The following steps are required:
Enable VBoxAuthSimple with the following command:
VBoxManage setproperty vrdeauthlibrary "VBoxAuthSimple"
To enable the library for a particular VM, you must then switch authentication to external:
VBoxManage modifyvm <vm> --vrdeauthtype external
Replace <vm> with the VM name or UUID.
You will then need to configure users and passwords by writing items into the machine's extradata. Since the XML machine settings file, into whose "extradata" section the password needs to be written, is a plain text file, VirtualBox uses hashes to encrypt passwords. The following command must be used:
VBoxManage setextradata <vm> "VBoxAuthSimple/users/<user>" <hash>
Replace <vm> with the VM name or UUID, <user> with the user name who should be allowed to log in and <hash> with the encrypted password. As an example, to obtain the hash value for the password "secret", you can use the following command:
VBoxManage internalcommands passwordhash "secret"
This will print
2bb80d537b1da3e38bd30361aa855686bde0eacd7162fef6a25fe97bf527a25b
You can then use VBoxManage setextradata to store this value in the machine's "extradata" section.
As example, combined together, to set the password for the user "john" and the machine "My VM" to "secret", use this command:
VBoxManage setextradata "My VM" "VBoxAuthSimple/users/john"
2bb80d537b1da3e38bd30361aa855686bde0eacd7162fef6a25fe97bf527a25b
Finally, the "guest" authentication method performs authentication with a special component that comes with the Guest Additions; as a result, authentication is not performed on the host, but with the guest user accounts.
This method is currently still in testing and not yet supported.
In addition to the methods described above, you can replace the default "external" authentication module with any other module. For this, VirtualBox provides a well-defined interface that allows you to write your own authentication module. This is described in detail in the VirtualBox Software Development Kit (SDK) reference; please see Chapter 11, VirtualBox programming interfaces for details.
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