KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q267560: Changing the URL May Expose Contents of a File

Article: Q267560
Product(s): Internet Information Server
Version(s): 4.0,5.0
Operating System(s): 
Keyword(s): kbWinNT400PreSP7Fix kbWin2000PreSP2Fix kbWin2000SP2Fix kbgraphxlinkcritical
Last Modified: 20-MAY-2002

-------------------------------------------------------------------------------
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:

  <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, 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 1986-2002.