Public Vulnerability Reports

Blue Coat WinProxy Telnet DoS Vulnerability



BlueCoat WinProxy is an Internet sharing proxy server designed for small
to medium businesses. In addition to Internet sharing Winproxy also
hosts a series of security, anti-spam and anti-spyware capabilities.

More information can be located from the vendors site at:


Remote exploitation of a design error in Blue Coat Systems Inc.'s
WinProxy allows attackers to cause a denial of service (DoS) condition.
The vulnerability can be triggered by sending a large string of 0xFF
characters to the telnet proxy port of the server. Sending such a string
will cause a heap corruption in the Winproxy process causing it to


Successful exploitation requires an attacker to send a stream of TCP
packets containing the 0xFF character to the WinProxy telnet server on
TCP port 23. This will lead to a crash of the server and it will be
unusable until it is restarted.

In lab tests, the heap corruption caused by this exploit led to cashes
in random locations in the process. The possibility for remote code
execution is possible, however will likely be very hard to control and
maintain reliable code execution.


iDefense has confirmed this vulnerability in WinProxy 6.0.

All previous versions are suspected to be vulnerable.


Disabling the WinProxy telnet protocol will prevent this attack.


Blue Coat has released WinProxy 6.1a to address this vulnerability.


The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-3654 to this issue. This is a candidate for inclusion in
the CVE list (, which standardizes names for
security problems.


11/15/2005   Initial vendor notification
11/15/2005   Initial vendor response
01/05/2006   Coordinated public disclosure


The discoverer of this vulnerability wishes to remain anonymous.

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Copyright © 2006 Verisign, Inc.

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