Memory leak in ISA Server H.323 Gatekeeper service and Winsock Proxy service when decoding malformed packets

It is possible for a memory leak in the Internet Security and Acceleration (ISA) Server Gatekeeper service and Winsock Proxy service to be exploited to deplete resources on the server. If this were to occur, the server could become slow and services could become unresponsive.

The Gatekeeper service in ISA Server allows for sophisticated call handling and routing of H.323 Voice over IP (VoIP) calls; the Winsock Proxy service allows internal users to gain access to Internet resources. Malformed packets that are directed at the services can cause the H323asn1.dll dynamic-link library (DLL) to consume system resources and not release them.

There is no memory leak if the Gatekeeper service is not started. The Gatekeeper service loads the H323asn1.dll DLL when it starts. Resources are handled typically if you have not configured your H.323 gateway, and such an attack would have no effect.

Service pack information

This problem was first corrected in Microsoft Internet Security and Acceleration Server 2000 Service Pack 1.
For additional information about how to obtain the latest ISA Server service pack, click the following article number to view the article in the Microsoft Knowledge Base:

Hotfix information

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that this article describes. Apply it only to systems that you determine are at risk of attack. Evaluate your computer's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to your computer. See the associated Microsoft Security Bulletin to help determine the degree of risk. This hotfix may receive additional testing. If your computer is sufficiently at risk, Microsoft recommends that you apply this hotfix now.

To resolve this problem immediately, download the hotfix by following the instructions later in this article or contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site: Note In special cases, charges that are ordinarily incurred for support calls may be canceled, if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.
The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Microsoft Internet Security and Acceleration (ISA) Server 2000.

For more information on this vulnerability, see the following Microsoft Web site: The fix that is described in this article also applies to the following Microsoft Knowledge Base article: