Full Disclosure: Re: Possible RDP vulnerability

["Thor (Hammer of God)" <Thor () hammerofgod com>]

I think you still misunderstand.

The option you refer to has nothing to do with "locking down" the server.  When you say things like "a locked down 
group policy that is tighter than a ducks bum" what exactly are you talking about?

Selecting "don't allow a startup program to be run" simply forces the desktop to be shown as opposed to an application 
one may specify.  If I initiate a session and tell it to run calc.exe, then calc.exe is what it presented upon 
connection.  It's a shortcut for the user.  If at the server I don't allow applications to be specified, then it won't 
run them and will default to the desktop.  But I can still go "start, run, calc" and it will run fine if I have 
permissions to run it.  AppLocker is a great way to lock down the host environment, whether RDP or not.

And you are quite incorrect about "no user based control" stopping you.  As mentioned, AppLocker could have prevented 
it had it been deployed "properly."  Well, it would help, anyway.   Depends on the manner in which the attack was 
carried out, of course, but that has nothing whatsoever to do with the setting in RDP.  Deploying RDP to untrusted 
users or malicious users is not good policy; as such, you need to take extra care in securing RDP hosts by using 
permissions and other restrictions.

I think you need to relax a little and think about what you post - saying things like "a GPO tighter to a ducks bum" 
and "open to total pwnage" and "nothing would stop me" sounds a bit hyperbolic (in addition to being incorrect).

To summarize, your concerns have nothing to do with RDP security settings as you have presented them.  MS10-015 is 
certainly an important issue for local-host based attacks, of which RDP is one.  One's mitigation efforts should indeed 
include RDP hosts.  The takeaway from that is to apply more due diligence to securing RDP deployments as one would with 
any asset you give users local access to.   RDP should not be viewed as a security mechanism, but rather, an access 
mechanism.  There are MANY ways to secure RDP, limit access, publish applications in singularity, create remote 
workspaces, etc, but you need to educate yourself on these solutions.

The behavior you describe is expected, by design behavior.

t

From: full-disclosure-bounces () lists grok org uk [mailto:full-disclosure-bounces () lists grok org uk] On Behalf Of 
wicked clown
Sent: Friday, March 26, 2010 8:31 AM
To: Full-Disclosure () lists grok org uk
Subject: Re: [Full-disclosure] Possible RDP vulnerability

Thank you for your comment.

What I was referring to it being scary is that if you create a locked down group policy that is tighter than a ducks 
bum and you forget that single tick (I admit I didn't knew of that option and I bet lots of other people didn't know 
about it) you leave your system to total pwnage!! It's simple mistakes like that which compromises systems.

If I found this before MS10-015 patch was released I could of download that exploit and gain system level permission, 
so no user based permission or access control would of stopped me.


On Fri, Mar 26, 2010 at 2:13 PM, Thor (Hammer of God) <Thor () hammerofgod com<mailto:Thor () hammerofgod com>> wrote:
There's nothing "scary" about it.   I believe you are incorrectly asserting that the inclusion of the "start the 
following program on connection" has something to do with "locking down the server" and/or "only allow(ing) users who 
connect to your server to run certain applications."   I would suggest that you study up on what RDP is and how it 
works before posting things like this.

Consider "locking down RDP" a process similar to "locking down a local host."  Use permissions and other host/OS based 
controls to secure what a user can and can't do on a host.

t



From: full-disclosure-bounces () lists grok org uk<mailto:full-disclosure-bounces () lists grok org uk> 
[mailto:full-disclosure-bounces () lists grok org uk<mailto:full-disclosure-bounces () lists grok org uk>] On Behalf Of 
wicked clown
Sent: Friday, March 26, 2010 3:33 AM

To: Full-Disclosure () lists grok org uk<mailto:Full-Disclosure () lists grok org uk>
Subject: Re: [Full-disclosure] Possible RDP vulnerability

Cheers for that,

I take it back that I haven't found an vulnerability :(, but by default this isn't enabled which is scary !!

On Fri, Mar 26, 2010 at 9:57 AM, Mr. Hinky Dink <dink () mrhinkydink com<mailto:dink () mrhinkydink com>> wrote:
There is a section in RCP-Tcp Properties on the server under "Environment" for "Do not allow an initial program to be 
launched.  Always show the desktop".

----- Original Message -----
From: wicked clown<mailto:wickedclownuk () googlemail com>
To: Full-Disclosure () lists grok org uk<mailto:Full-Disclosure () lists grok org uk>
Sent: Friday, March 26, 2010 5:04 AM
Subject: [Full-disclosure] Possible RDP vulnerability

Hi Guys,

I think I possible may have found a vulnerability with using RDP / Terminal services on windows 2003.

If you lock down a server and only allow users who connect to your RDP connection to run certain applications, users 
can bypass this and run ANY application they want. You can do this by modifying the RDP profile / shortcut and add your 
application to the alternate shell and the shell working directory.

When the user connects now to the RDP server the banned application will execute upon logging on even though the user 
isn't allowed to execute the application if the user logs on normally. This doesn't work with cmd.exe but I have been 
able to execute internet explorer, down a modified cmd version, modify the RDP profile to execute the new cmd and it 
works like a charm.

I have only been able to tested this on windows 2003 using a local policy and works like a treat. Even in the wild!

I have done a quick basic video which can been seen here;
http://www.tombstone-bbs.co.uk/v1d30z/rdp-hack2.swf

Instead of modifying the RDP profile, I just added my application to the program tab.. I know the video is crappy but 
it's just meant to give you an idea what I am talking about :)

So in short, if anybody can access your server via RDP they are NOT restricted by the policy. I would be interested in 
any feed back about this possible exploit / vulnerability even if you don't think it is.. or even better if someone 
knows how to defend againest it!! LOL! :)

Cheers

Wicked Clown.
________________________________
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_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/


_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/