Re: [Full-disclosure] RDP, can it be done safely?

["Thor (Hammer of God)" <Thor@xxxxxxxxxxxxxxx>]

Hey Jeffery - sorry for the top post reply...   What I was saying (in response 
to Larry) is that the "require a VPN to connect first" doesn't necessarily buy 
you anything from a security perspective as opposed to directly publishing 
terminal services.    What I meant to say (though I didn't really say it well 
last night) was that if you connect to the VPN with the same credentials that 
you would then connect to the TS box once connected to the VPN, that you really 
haven't bought yourself anything - you may as well just directly connect to the 
RDP server.  While this could be done via 3389 directly (or any port for that 
matter) I personally would use TSG over 443.  But I don't necessarily require 
VPN first.  I personally haven't VPNd into my own network for many years now.  
I just RDP directly to my resources.  

My "full stack" comment meant to point out that if you set up a VPN for the 
purposes of getting to an RDP resource internally, that that could actually be 
less secure than a "direct" connection to rdp since you are only allowing the 
one port into your network from the client as opposed to that client having a 
full pipe to the rest of the network.  That point, however, gets lost in the 
reality of "well, you are on the remote desktop of a box on the network so 
what's the difference" but I still think it is a valid point.  

Hopefully that comes across better than my message last night - I was knee deep 
in a lot of stuff last night and my email was not all that clear. ;)

t

-----Original Message-----
From: Jeffrey Walton [mailto:noloader@xxxxxxxxx] 
Sent: Thursday, June 10, 2010 7:21 AM
To: Thor (Hammer of God)
Cc: Larry Seltzer; Daniel Sichel; full-disclosure@xxxxxxxxxxxxxxxxx
Subject: Re: [Full-disclosure] RDP, can it be done safely?

Hi Thor,

> I only bring this up because I think one should consider the 
> ramifications of the "VPN first" model before assuming it grants you 
> some inherent security.
My experience in the enterprise and the work-at-home crowd has been:
(1) VPN into corpnet
(2) Land at a TS (users) or JumpBox (Admins)

I've read your reply a few times, so please forgive my ignorance: What are you 
claiming? (1) There are technologies other than VPN? (2) Don't use VPN? (3) Use 
Windows Firewall and IP filtering? (4) Use RDP over HTTPS for single sign on? 
Again, my apologies.

> However, when it comes to a network-level "least privilege"
> standpoint, I think there are stark differences:  The VPN endpoint 
> typically will give the end user full-stack IP acces
>  to resources unless otherwise specified.
In this respect, how is VPN any different than a user walking in to the office, 
punching in, and signing on at the computer in their cube?

For the Admin, its allow VPN to TS or jumpbox. Then network security applies. 
Or am I missing something in your statements?

> RDP endpoints however only require the specified RDP port to access the host.
This is kind of Apples and Oranges.... The vpn GIVES acces to TCP/IP, while rdp 
REQUIRES that 3389 be open on the host. Perhaps I misread you.

Jeff

On Wed, Jun 9, 2010 at 11:58 PM, Thor (Hammer of God) <Thor@xxxxxxxxxxxxxxx> 
wrote:
>
> I request that you start thinking about RDS/TS/RDP as a "direct" technology.  
> Treating access via RDP as something that one must first VPN/RAS into a 
> corpnet first in order to secure properly obscures what one might consider 
> obvious:
>
> If you require me to logon to your network via VPN first before I can 
> subsequently connect to internal RDP resources, one might consider the VPN 
> endpoint as the primary authentication point.  As such, one might logically 
> conclude that since access was granted via the VPN, that internal access to 
> RDP resources would be considered "safe."  In this model, what is the 
> difference between me authenticating to the VPN endpoint as opposed to me 
> authenticating to an RDP endpoint?
>
> Insofar as the authentication layer is concerned, there really isn't a 
> difference.  However, when it comes to a network-level "least privilege" 
> standpoint, I think there are stark differences:  The VPN endpoint typically 
> will give the end user full-stack IP access to resources unless otherwise 
> specified.  RDP endpoints however only require the specified RDP port to 
> access the host.  What happens after a successful connection to the host is 
> up to the admin.   In the case of RDP via TSGateway, we find that one can 
> deploy a server at the "connection-level" using client certificates - not 
> only for encryption upon connection, but for validation TO connect in the 
> first place.
>
> To me, that is an important distinction.
>
> VPN endpoint authentication might lead to the propensity for one to consider 
> access to down-range resources as authorized.  I don't think you should do 
> that when you consider the capabilities an attacker has given an "open pipe" 
> once authenticated versus an single protocol access to a machine you can 
> tightly control.
>
> I only bring this up because I think one should consider the ramifications of 
> the "VPN first" model before assuming it grants you some inherent security.
>
> t
>
>  [SNIP]

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