Changing the URL in a specific manner may expose contents of a file

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Article ID: 267560
This article was previously published under Q267560
This article has been archived. It is offered "as is" and will no longer be updated.
We strongly recommend that all users upgrade to Microsoft Internet Information Services (IIS) version 7.0 running on Microsoft Windows Server 2008. IIS 7.0 significantly increases Web infrastructure security. For more information about IIS security-related topics, visit the following Microsoft Web site:
http://www.microsoft.com/technet/security/prodtech/IIS.mspx
For more information about IIS 7.0, visit the following Microsoft Web site:
http://www.iis.net/default.aspx?tabid=1
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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 Microsoft security bulletin and in the following Microsoft Knowledge Base article:
Microsoft Security Bulletin (MS00-031)
http://www.microsoft.com/technet/security/bulletin/ms00-031.mspx
260069 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.

Resolution

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 more information, click the following article number to view the article in the Microsoft Knowledge Base:
260910 How to obtain the latest Windows 2000 service pack
The following file is available for download from the Microsoft Download Center:
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Download
Download Q267559_w2k_sp2_x86_en.exe now
For more 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 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 hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next Windows NT 4.0 service pack that contains this hotfix.

To resolve this problem immediately, 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 files are available for download from the Microsoft Download Center:

x86:
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Download
Download Htrdos4i.exe now
x86 symbols:
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Download
Download Htrdos4is.exe now
Alpha:
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Download
Download Htrdos4a.exe now
Alpha symbols:
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Download
Download Htrdos4as.exe now
For more 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 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 that this is 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

What does the patch do?

This patch eliminates the vulnerability by causing the malformed URL to be rejected.

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:
<b>Some HTML text</b> 
<% 
/*Some <file://Some/> ASP/HTR code*/ 
var objConn = new ActiveXObject("Foo.bar"); 
%> 
<I>other html code</I> 
other code.
				
The information that is returned to the malicious user is:
<b>Some HTML text</b> 
<I>other html code</I> 
other code.
				

Related Security Bulletin

For more information, see the Microsoft Security Bulletin at http://www.microsoft.com/technet/security/bulletin/ms00-044.mspx.

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.

Properties

Article ID: 267560 - Last Review: October 26, 2013 - Revision: 8.0
Keywords: 
kbnosurvey kbarchive kbbug kbfix kbgraphxlinkcritical kbwin2000presp2fix KB267560

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