BugTraq
DoS attack on Windows 2000 Terminal Server Jan 23 2003 11:29AM
Jonathan Hunter jonathan.hunter+dated+1043753340.86cf13 (at) ptel.co (dot) uk [email concealed] (jonathan hunter+dated+1043753340 86cf13 ptel co uk)
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!

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