DoS attack on Windows 2000 Terminal Server

2008.02.14
Risk: Low
Local: Yes
Remote: No
CWE: N/A


CVSS Base Score: 6.8/10
Impact Subscore: 6.9/10
Exploitability Subscore: 8/10
Exploit range: Remote
Attack complexity: Low
Authentication: Single time
Confidentiality impact: None
Integrity impact: None
Availability impact: Complete

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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