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Category:   Application (Generic)  >   WinGate Vendors:   Qbik IP Management Limited
WinGate DNS Request Processing Bug Lets Remote Users Deny Service
SecurityTracker Alert ID:  1017284
SecurityTracker URL:
CVE Reference:   CVE-2006-4518   (Links to External Site)
Date:  Nov 27 2006
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  
Version(s): 6.1.4 and prior versions
Description:   A vulnerability was reported in WinGate. A remote user can cause denial of service conditions.

A remote user can send specially crafted DNS request containing a self-referencing compressed name pointer to cause the target service to consume all available CPU resources.

The vendor was notified on August 17, 2006.

Michael Sutton of iDefense Labs discovered this vulnerability.

Impact:   A remote user can cause denial of service conditions.
Solution:   The vendor has issued a fixed version (6.2).
Vendor URL: (Links to External Site)
Cause:   State error
Underlying OS:  Windows (Any)

Message History:   None.

 Source Message Contents

Subject:  [Full-disclosure] iDefense Security Advisory 11.26.06: Qbik WinGate

Qbik WinGate Compressed Name Pointer Denial of Service Vulnerability

iDefense Security Advisory 11.26.06
Nov 26, 2006


Qbik WinGate is an Internet gateway and communications server. It includes
functionality related to efficiently sharing an Internet connection
including DNS caching.

More information is available at the following link:


Remote exploitation of a denial of service vulnerability in Qbik IP
Management Limited's WinGate allows attackers to cause the application to
consume 100% of available CPU cycles.

Sending a DNS request which contains a compressed name pointer which
references itself, will cause the vulnerable code to enter an infinite
loop which will consume all CPU cycles. The following packet illustrates
the DNS data that would be included in a packet triggering this

\x00\x00 - Transaction ID
\x00\x00 - Flags
\x00\x01 - Questions
\x00\x00 - Answer RRs
\x00\x00 - Authority RRs
\x00\x00 - Additional RRs
\xc0\x0c - Query Name - Looping pointer
\x00\x00 - Query Type
\x00\x01 - Query Class

The DNS protocol allows for the compression of domain names in order to
reduce message sizes. This is accomplished by replacing an entire domain
name or a list of labels at the end of a domain name with a pointer to a
prior occurrence of the same name. The use of a pointer is indicated
within the Query Name field when the first two bits equal 1 (e.g. 0x0c).
The next byte is then interpreted as a pointer. In the packet detailed
above, the pointer itself is at the 12th byte within the DNS data portion
of the packet, thereby creating a looping pointer. The DNS compression
scheme is discussed in detail in RFC 1035.


Successful exploitation of this vulnerability could prevent the WinGate
proxy from functioning and thereby deny legitimate users access to network
based resources. This vulnerability can be triggered by any user that is
able to send packets to the WinGate proxy. A single UDP packet is all that
is required and authentication credentials are not needed.


iDefense has confirmed that Qbik Wingate 6.1 is vulnerable. Earlier
versions are suspected vulnerable.


iDefense is unaware of an effective workaround for this issue.


"Qbik acknowledges this to be a bug in WinGate version 6.1.4 and prior."

Qbik addressed this vulnerability within version 6.2.


The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2006-4518 to this issue. This is a candidate for inclusion in
the CVE list (, which standardizes names for
security problems.


08/17/2006  Initial vendor notification
10/17/2006  Initial vendor response
10/17/2006  Second vendor notification
11/26/2006  Coordinated public disclosure


Michael Sutton (iDefense Labs) is credited with the discovery of this

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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 e-mail 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

Full-Disclosure - We believe in it.
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