Public Vulnerability Reports

Qbik WinGate Compressed Name Pointer Denial of Service Vulnerability



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 vulnerability:

x00x00 - Transaction ID
x00x00 - Flags
x00x01 - Questions
x00x00 - Answer RRs
x00x00 - Authority RRs
x00x00 - Additional RRs
xc0x0c - Query Name - Looping pointer
x00x00 - Query Type
x00x01 - 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 RFC1035.


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


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

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Copyright © 2006 Verisign, Inc.

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