The following is a Security Bulletin from the Microsoft Product Security
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Microsoft Security Bulletin (MS00-019)
Patch Available for "Virtualized UNC Share" Vulnerability
Originally Posted: March 30, 2000
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Internet Information Server and
products based on it. Under certain fairly unusual conditions, the
vulnerability could cause a web server to send the source code of
.ASP and other files to a visiting user.
Frequently asked questions regarding this vulnerability and the patch
can be found at
If a virtual directory on an IIS server is mapped to a UNC share, and
a request for a file in the directory contains one of several
particular characters at the end, the expected ISAPI extension
processing may not occur. The result is that the source code of the
file would be sent to the browser.
There are significant restrictions that would increase the difficulty
of exploiting this vulnerability:
- By design, virtual directories hide the actual location of files.
Under most circumstances, there would be no way for an attacker to
determine which files on a server actually reside on a UNC share.
- Many browsers will "correct" requests that contain the trailing
characters at issue here, by either removing the characters or
- If recommended security practices are followed, .ASP and other
files that require server-side processing will not contain any
sensitive information to compromise.
Affected Software Versions
- Microsoft Internet Information Server 4.0 and 5.0
- Microsoft Proxy Server 2.0
- Microsoft Site Server and Site Server, Commerce Edition 3.0
- Microsoft Commercial Internet System 2.0 and 2.5
- Internet Information Server 4.0
- Internet Information Server 5.0
NOTE: Proxy Server, Site Server, Site Server Commerce Edition and
Microsoft Commercial Internet System run atop IIS. Customers using
these products should apply the patch appropriate for the version of
IIS they are running.
NOTE: Additional security patches are available at the Microsoft
Please see the following references for more information related to
- Frequently Asked Questions: Microsoft Security Bulletin MS00-019,
- Microsoft Knowledge Base (KB) article Q249599,
Virtual Directory Mapped to UNC Returns Server-Side Script Code
When URL Contains Additional Characters at the End of the Request,
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
- March 30, 2000: Bulletin Created.