DOCUMENT:Q267560 20-MAY-2002 [iis] TITLE :Changing the URL May Expose Contents of a File PRODUCT :Internet Information Server PROD/VER::4.0,5.0 OPER/SYS: KEYWORDS:kbWinNT400PreSP7Fix kbWin2000PreSP2Fix kbWin2000SP2Fix kbgraphxlinkcritical ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Internet Information Services version 5.0 - Microsoft Internet Information Server version 4.0 ------------------------------------------------------------------------------- SYMPTOMS ======== Fragments of a .asp, Global.asa, or other files may be retrieved from a Web server when the URL is changed in a specific manner. CAUSE ===== This issue is a variant of the vulnerability that was originally discussed in the following security bulletin and Microsoft Knowledge Base article: Microsoft Security Bulletin (MS00-031) (http://www.microsoft.com/technet/security/bulletin/ms00-031.asp) Q260069 Malformed HTR Request Returns Source Code for ASP Scripting Files This new issue is simply an additional way to exploit the same vulnerability. Because of this vulnerability, a malicious user may be able to request files from the server, which are then processed as though they were .htr files. This can result in parts of the .asp or other file's source code being sent to the malicious user. NOTE: In theory, this vulnerability can expose sensitive data contained in the .asp files. However, in practice, it's unlikely that this would occur. The HTR processing tends to remove the very content that would be of interest to the malicious user. Disable HTR Functionality: If you do not have business-critical .htr scripts, perform the following steps to disable the .htr functionality: 1. Open the Internet Services Manager. 2. Right-click the Web server, click Properties, click Master Properties, and then click WWW Service. 3. Click Edit, click Home Directory, and then click Configuration. 4. Remove the .htr entry. Apply the Patch: For customers with business-critical HTR scripts who need to retain .htr functionality and therefore can't disable .htr functionality, the following patch is available that corrects these issues. For Windows 2000 ---------------- To resolve this problem, obtain the latest service pack for Windows 2000. For additional information, please see the following article in the Microsoft Knowledge Base: Q260910 How to Obtain the Latest Windows 2000 Service Pack The following file is available for download from the Microsoft Download Center: DownloadDownload Q267559_w2k_sp2_x86_en.exe now (http://www.microsoft.com/Downloads/Release.asp?ReleaseID=22708) 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 Time Version Size File name ----------------------------------------------------- 07/07/2000 03:17p 5.00.2195.2100 46,352 Ism.dll For Windows NT 4.0 ------------------ 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 experiencing this specific problem. This fix may receive additional testing at a later time, to further ensure product quality. Therefore, if you are not severely affected by this problem, Microsoft recommends that you wait for the next Windows NT 4.0 service pack that contains this fix. 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 files are available for download from the Microsoft Download Center: x86: DownloadDownload Htrdos4i.exe now (http://www.microsoft.com/Downloads/Release.asp?ReleaseID=22709) x86 symbols: DownloadDownload Htrdos4is.exe now (http://www.microsoft.com/Downloads/Release.asp?ReleaseID=22709) Alpha: DownloadDownload Htrdos4a.exe now (http://www.microsoft.com/Downloads/Release.asp?ReleaseID=22709) Alpha symbols: DownloadDownload Htrdos4as.exe now (http://www.microsoft.com/Downloads/Release.asp?ReleaseID=22709) 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 Time Version Size File name Platform ---------------------------------------------------------- 06/28/2000 09:34p 4.2.748.1 54,544 Ism.dll x86 06/28/2000 09:30p 4.02.0748 84,752 Ism.dll Alpha STATUS ====== Microsoft has confirmed this to be a problem in Internet Information Services 5.0 and Internet Information Server 4.0. This problem was first corrected in Windows 2000 Service Pack 2. MORE INFORMATION ================ For additional information about how to install Windows 2000 and Windows 2000 hotfixes at the same time, click the article number below to view the article in the Microsoft Knowledge Base: Q249149 Installing Microsoft Windows 2000 and Windows 2000 Hotfixes What does the patch do?: This patch eliminates the vulnerability by causing the malformed URL to be rejected. For additional information about what this patch fixes, click the article numbers below to view the articles in the Microsoft Knowledge Base: Q267599 GET on HTR File Can Cause a "Denial of Service" or Enable Directory Browsing Q260838 IIS Stops Servicing HTR Requests Q260069 Malformed HTR Request Returns Source Code for ASP Scripting Files What does this vulnerability allow a malicious user to do? : Microsoft Security Bulletin MS00-031 provides the best description of the vulnerability and the risk it poses. However, in a nutshell, the vulnerability can allow a malicious user to request files from the server, which would then be processed as though they were .htr files. The result of this can be that parts of the ASP source code are sent to the malicious user. Which parts of the .asp source code are likely to be sent?: The ISAPI filter attempts to interpret the requested file as a .htr file, which has the effect of removing virtually everything but the text from a selected file. That is, it strips out the very information that is most likely to contain sensitive information in .asp and other server-side files. For example, if this vulnerability is used to try to read a file with the following contents: Some HTML text <% /*Some ASP/HTR code*/ var objConn = new ActiveXObject("Foo.bar"); %> other html code other code. The information that is returned to the malicious user is: Some HTML text other html code other code. Related Security Bulletin: For more information, please see the Microsoft Security Bulletin at http://www.microsoft.com/technet/security/bulletin/ms00-044.asp What is HTR?: HTR is a first-generation advanced scripting technology that is included in IIS 3.0, and still supported by later versions of IIS for backwards compatibility. However, HTR was never widely adopted, and was superceded by Active Server Pages (ASP) technology introduced in IIS 4.0. Additional query words: nt winnt Windows 2000 win2k DoS attack vulnerability security hack hacker folder argument risk akz ====================================================================== Keywords : kbWinNT400PreSP7Fix kbWin2000PreSP2Fix kbWin2000SP2Fix kbgraphxlinkcritical Technology : kbiisSearch kbiis500 kbiis400 Version : :4.0,5.0 Hardware : 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. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2002.