I have a CentOS 7 installation running Virtualbox 5.1.8, and the Oracle VM Virtualbox Extension Pack 5.1.8 is also installed. I have a few guests (CentOS as well) running and I would like to access one of them via RDP with external authentication.

So I enabled the VRDP server, and I can't seem to connect, not from the host machine (localhost) nor from a different Windows machine. It simply seems to time out.

However, if I set the authentication method to null, it works perfectly fine. But I don't want to use null authentication.

Is there something I'm missing?

EDIT: I just noticed that if I select null authentication, I can only login via localhost, not from an external machine, which is even more strange...

1 Answer 1


I've had pretty same problem after upgrading from 4.3.36 to 5.1.26 on debian 9.

I'm using external authentication with "VBoxAuthSimple" performing authentication against credentials configured in the "extradata" section of VM.

In 4.3.36 everything worked fine but through VNC protocol.

In 5.1.26 RDP protocol is now used and the problem was that gui clients, like default RDP in windows and default rdesktop in debian doesn't allow to enter password during connection (window with password prompt appears after establishing connection) and you've got an error in vbox log "external authentication module returned 'access denied'".

Null authentication works fine though.

Solution: use cli to pass user and password simultaneously

rdesktop-vrdp -u <user> -p <password> server:port

For windows save password hash in .rdp file you using for connection or you can use client that allows password in configuration, for example http://www.parallels.com/ru/products/ras/download/client/

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