DOCUMENT:Q305359 08-MAY-2002 [iis] TITLE :Incorrect Content Length May Cause Web Services to Fail PRODUCT :Internet Information Server PROD/VER::4.0 OPER/SYS: KEYWORDS:kbWinNT400PreSP7Fix ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Internet Information Server version 4.0 ------------------------------------------------------------------------------- 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 (http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS01-033.asp). 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 fix is now available from Microsoft, but it is only intended to correct the problem described in this article and should be applied only to systems that are determined to be at risk of attack. Please evaluate your computer's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to your computer. Please see the associated Microsoft Security Bulletin (http://www.microsoft.com/technet/security/bulletin/ms01-044.asp) to help make this determination. This fix may receive additional testing at a later time, to further ensure product quality. If your computer is sufficiently at risk, Microsoft recommends that you apply this fix now. To resolve this problem immediately, download the fix as instructed below or contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web: http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS NOTE: In special cases, charges that are normally incurred for support calls may be canceled, if a Microsoft Support Professional determines that a specific update will resolve your problem. Normal 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: DownloadDownload Q301625i.exe now (http://www.microsoft.com/Downloads/Release.asp?ReleaseID=32061) 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 article number below to view the article in the Microsoft Knowledge Base: Q119591 How to Obtain Microsoft Support Files from Online Services Microsoft used the most current virus detection software available on the date of posting to scan this file for viruses. After it is posted, the file is housed on secure servers that 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 could result in some 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: Q297860 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.asp 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 : kbWinNT400PreSP7Fix Technology : kbiisSearch kbiis400 Version : :4.0 Hardware : ALPHA x86 Issue type : kbbug Solution Type : kbfix ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. 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