DoS attack on Windows 2000 Terminal Server

[Jonathan Hunter]

This one's short and simple..

Description
-----------

Any user with sufficient permission to log on to a Windows 2000 Terminal
Server (via RDP or ICA) and access its filesystem can reboot the server
at will.


Exploit
-------

- Open %SYSTEMROOT%\SYSTEM32\MSGINA.DLL for exclusive access (read lock).
I used Radsoft's HEXVIEW.EXE from Rix2K to do this.

- Open a new connection to the server via RDP/ICA

- Click the nice, helpful "Restart" button in the warning dialog that
appears ("msgina.dll failed to load")

Tested on Windows 2000 Server (IE55, SP2) and Windows 2000 Server (IE55,
SP3). I do not have easy access to other platforms at the moment.


Workaround
----------

- Remove all permissions from MSGINA.DLL for "Power Users", "Users" and
"Everyone"

Note: The above workaround has been tested on Windows 2000 Server (IE55,
SP2) and users were still able to log in as normal. I am not aware of a
need for MSGINA.DLL to be accessible by normal users, but if there are
any such circumstances Microsoft will need to produce an alternative fix.


Vendor status
-------------

Contacted on 16/01/2003. Replied to my email the next day requesting
additional time to investigate. No further replies since 17/01/2003.


Thanks
------

Thanks to PPH for the use of a Windows 2000 Server IE55,SP2 machine!

[Diogo Fernandes]

Hi, all

> Tested on Windows 2000 Server (IE55, SP2) and Windows 2000 Server
(IE55, SP3). I do not have easy access to other
> platforms at the moment.

Tested on Windows Xp Professional, w/o SP. The problem exists.


> Workaround
> - Remove all permissions from MSGINA.DLL for "Power Users", "Users"
and
> "Everyone"

We have a problem here. If you try to change permissions from
MSGINA.DLL, you get a warning, talking about to change the parent
permissions, too. As my experience is in Unices systems, what kind of
problems can I have if I change the permissions of my WINNT folder ?



Diogo Carlos Fernandes
Technical Support Manager

Real Media Latin America
www.realmedia.com

Phone .: 55+11+3842-2166
Mobile .: 55+11+9266-5325
e-mail .: dfernandes@realmedia.com