Microsoft KB Archive/305359

= Incorrect Content Length May Cause Web Services to Fail =

Article ID: 305359

Article Last Modified on 10/10/2006

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APPLIES TO


 * Microsoft Internet Information Server 4.0

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This article was previously published under Q305359



SYMPTOMS
Internet Information Server (IIS) 4.0 may shut down and generate a Dr. Watson report when the Web service receives a request with an incorrect Content Length in the HTTP Request.

This vulnerability is being actively exploited by the Code Red worm virus. This vulnerability has been widely, although incorrectly, reported as being due to a flaw in the patch provided in Microsoft Security Bulletin MS01-033. In fact, this is a completely different and previously unknown vulnerability.



CAUSE
This problem most often occurs when the Web server is configured to perform Web site redirections or when the Web server is configured to respond with an HTTP 301 redirect or HTTP 302 redirect. It is important to note that this is not the default configuration of an IIS 4.0 installation.



RESOLUTION
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 the computer's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to the computer. See the associated Microsoft Security Bulletin to help determine the degree of risk. This hotfix may receive additional testing. If the computer is sufficiently at risk, we recommend 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 telephone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

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 following file is available for download from the Microsoft Download Center:

Download Q301625i.exe now

NOTE: Q301625is.exe contains the Symbols files.

NOTE: This patch can be installed on systems running Windows NT 4.0 Service Pack 5 or Windows NT 4.0 Service Pack 6a.

Release Date: August 15, 2001

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

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:

  Date         Version    Size     File name --  10-Aug-2001  4.2.769.1  229,536  W3svc.dll



STATUS
Microsoft has confirmed that this problem may cause a degree of security vulnerability in Internet Information Server 4.0.



MORE INFORMATION
This patch also contains fixes for the problems described in the following Microsoft Knowledge Base article:

297860 IIS 5.0 Security and Post-Windows NT 4.0 SP5 IIS 4.0 Patch Rollup

For more information on this vulnerability, see the following Microsoft Web site:

http://www.microsoft.com/technet/security/bulletin/ms01-044.mspx

Installing MS01-033 does not prevent the possibility of this vulnerability occurring. You must install the latest IIS 4.0 Security Rollup Package to eliminate this vulnerability. The vulnerability discussed in this Knowledge Base article is a problem that is simply exposed by the Code Red worm virus; it is not the intended results of the virus.

When a request sends data to an IIS 4.0 Web server and the Content Length is set to a value lower than the amount of data being sent, an access violation in IIS 4.0 occurs. When a Web site is set up for Web site redirection or the response to the client is a 301 or a 302, the IIS 4.0 system will more than likely fail with an access violation. The Code Red worm generates these types of requests when it tries to infect new computers. The patch provided in MS01-033 causes the requests to be treated as invalid, which prevents the infection. However, if URL redirection is enabled, the Web server may fail with an access violation followed by a Dr. Watson report.

IIS 5.0 systems are not affected by this newly discovered vulnerability. IIS 4.0 systems are only affected if they are configured to perform URL redirection, which is not the default configuration. Installing this patch resolves this vulnerability.

Additional query words: security_patch dos

Keywords: kbbug kbfix kbqfe KB305359

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