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Microsoft Security Bulletin (MS99-013)
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Solution Available for File Viewers Vulnerability
Originally Posted: May 7, 1999
Summary
=======
Microsoft has identified a vulnerability that occurs in some file viewers
that ship as part of Microsoft (r) Internet Information Server and Site
Server. The vulnerability could allow a web site visitor to view, but not to
change, files on the server, provided that they knew or guessed the name of
each file and had access rights to it based on Windows NT ACLs.
Microsoft is releasing this security bulletin to inform customers of the
vulnerability and enable them to eliminate it immediately. Patches are being
developed for the affected file viewers, and will be available shortly. When
they are available, an update to this security bulletin will be released.
Issue
=====
Microsoft Site Server and Internet Information Server include tools that
allow web site visitors to view selected files on the server. These are
installed by default under Site Server, but must be explicitly installed
under IIS. These tools are provided to allow users to view the source code
of sample files as a learning exercise, and are not intended to be deployed
on production web servers. The underlying problem in this vulnerability is
that the tools do not restrict which files a web site visitor can view.
It is important to note several important points:
- These file viewers are not installed by default under IIS.
They are only installed under IIS if the user chooses to install
the sample web files.
- This vulnerability only allows a web site visitor to view files.
There is no capability through this vulnerability to change files
or add files to the server.
- This vulnerability does not in any way bypass the Windows NT file
permission ACLs. A web site visitor could only use these tools to
view files whose ACLs allows them read access. The administrator of
the web server determines the specific permissions for all files on
the server.
- The viewers can only be used to view files on the same disk partition
as the currently-displayed web page. Databases such as those used by
e-commerce servers are typically stored on a different physical drive,
and these would not be at risk
- The web site visitor would need to know or guess the name of each file
they wished to view.
Specific steps that customers can take to immediately eliminate the
vulnerability are discussed below in What Customers Should Do. In addition,
Microsoft is developing updated versions of the file viewers and will
release them shortly.
While there are no reports of customers being adversely affected by this
vulnerability, Microsoft is proactively releasing this bulletin to allow
customers to take appropriate action to protect themselves against it.
Affected Software Versions
==========================
- Microsoft Site Server 3.0, which is included with Microsoft Site
Server 3.0 Commerce Edition, Microsoft Commercial Internet
System 2.0, and Microsoft BackOffice Server 4.0 and 4.5
- Microsoft Internet Information Server 4.0
What Microsoft is Doing
=======================
Microsoft has provided this bulletin to inform customers of specific steps
that they can take to immediately eliminate this vulnerability on their
servers. Microsoft is developing updated file viewers that fix the problem
identified, and will release an updated version of this bulletin when they
are available.
Microsoft also has sent this security bulletin to customers subscribing
to the Microsoft Product Security Notification Service. See
http://www.microsoft.com/security/services/bulletin.asp for more
information about this free customer service.
Microsoft has published the following Knowledge Base (KB) article on this
issue:
- Microsoft Knowledge Base (KB) article Q231368,
Solution Available for File Viewers Vulnerability,
http://support.microsoft.com/support/kb/articles/q231/3/68.asp.
(Note: It might take 24 hours from the original posting of this
bulletin for the KB article to be visible in the Web-based
Knowledge Base.)
What Customers Should Do
========================
Customers should take the following steps to eliminate the vulnerability on
their web servers:
- Unless the affected file viewers are specifically required on the
web site, they should be removed. The following file viewers are
affected: ViewCode.asp, ShowCode.asp, CodeBrws.asp and Winmsdp.exe.
Depending on the specific installation, not all of these files may
be present on a server. Likewise, there may be multiple copies of
some files, so customers should do a full search of their servers
to locate all copies.
- In accordance with standard security guidelines, file permissions
should always be set to enable web visitors to access only the files
they need, and no others. Moreover, files that are needed by web
visitors should provide the least privilege needed; for example,
files that web visitors need to be able to read but not write should
be set to read-only.
- As a general rule, sample files and vroots should always be deleted
from a web server prior to putting it into production. If they are
needed, file access permissions should be used to regulate access to
them as appropriate
More Information
================
Please see the following references for more information related to this
issue.
- Microsoft Security Bulletin MS99-013,
Solution Available for File Viewers Vulnerability
(The Web-posted version of this bulletin),
http://www.microsoft.com/security/bulletins/ms99-013.asp.
- Microsoft Knowledge Base (KB) article Q231368,
Solution Available for File Viewers Vulnerability,
http://support.microsoft.com/support/kb/articles/q231/3/68.asp.
Obtaining Support on this Issue
===============================
If you require technical assistance with this issue, please contact
Microsoft Technical Support. For information on contacting Microsoft
Technical Support, please see
http://support.microsoft.com/support/contact/default.asp.
Acknowledgments
===============
Microsoft acknowledges WebTrends (www.webtrends.com) for discovering this
vulnerability and reporting it to us.
Revisions
=========
- May 07, 1999: Bulletin Created.
For additional security-related information about Microsoft products, please
visit http://www.microsoft.com/security
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