IIS: Malformed URL Can Cause Service Failure in IIS 5.0 and Exchange 2000 Server

Microsoft Internet Information Services (IIS) 5.0 contains a flaw that affects the way that a URL is handled if it has a specific construction and its length is within a very narrow range of values. If such a URL were repeatedly sent to an affected system, a confluence of events could cause a memory allocation error that would result in the failure of the IIS service.

IIS 5.0 is affected by the same vulnerability as the Microsoft Exchange 2000 Server vulnerability that is described in the following article in the Microsoft Knowledge Base: Mitigating factors:

• The vulnerability would not enable the attacker to gain any administrative control over the server or to alter any data on it.
• The affected services automatically restart in the event of a failure; therefore, an affected system would resume service almost immediately.
• A successful attack against an Exchange server would only disrupt Web-based mail clients' use of the server. The server would continue to be available for MAPI-based clients such as Microsoft Outlook.
• The ISAPI involved in this vulnerability authenticates the user before servicing the request; therefore, a properly configured Exchange server would be at less risk than an IIS server.

To resolve this problem, obtain the latest service pack for Windows 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base: IMPORTANT: Because the flaw occurs in two different code modules, one of which is installed as part of IIS 5.0 and both of which are installed as part of Exchange 2000, it is important for Exchange 2000 administrators to install both the IIS and Exchange patches below.

The following files are available for download from the Microsoft Download Center:
For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. The English version of this fix should have the following file attributes or later:

Microsoft has confirmed that this is a problem in Microsoft Internet Information Services 5.0. This problem was first corrected in Windows 2000 Service Pack 2.

For additional information about how to obtain a hotfix for Windows 2000 Datacenter Server, click the article number below to view the article in the Microsoft Knowledge Base: For additional information about how to install multiple hotfixes with only one reboot, click the article number below to view the article in the Microsoft Knowledge Base: For more information about this issue, see the following Microsoft Web site: For additional information about how to install Microsoft Windows 2000 and Microsoft Windows 2000 hotfixes at the same time, click the article number below to view the article in the Microsoft Knowledge Base: