Blue Coat WinProxy Telnet DoS Vulnerability

Credit: iDEFENSE Labs
Risk: Medium
Local: No
Remote: Yes

Blue Coat WinProxy Telnet DoS Vulnerability iDefense Security Advisory 01.05.06 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: 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 (, 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. Get paid for vulnerability research Free tools, research and upcoming events X. LEGAL NOTICES Copyright © 2006 iDefense, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDefense. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice (at) idefense (dot) com [email concealed] for permission. 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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