Blue Coat WinProxy Telnet DoS Vulnerability

iDefense Security Advisory 01.05.06
http://www.idefense.com/intelligence/vulnerabilities/display.php?id=365
January 05, 2006

I. BACKGROUND

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:

  http://www.winproxy.com/

II. DESCRIPTION

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
crash.

III. ANALYSIS

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.

IV. DETECTION

iDefense has confirmed this vulnerability in WinProxy 6.0.

All previous versions are suspected to be vulnerable.

V. WORKAROUND

Disabling the WinProxy telnet protocol will prevent this attack.

VI. VENDOR RESPONSE

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

VII. CVE INFORMATION

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 (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

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

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright © 2006 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.
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