Microsoft Security Bulletin (MS00-057)
Patch Available for "File Permission Canonicalization" Vulnerability
Originally posted: August 10, 2000
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Internet Information Server. Under very
restricted conditions, the vulnerability could allow a malicious user
to gain additional permissions to certain types of files hosted on a
Frequently asked questions regarding this vulnerability and the patch
can be found at
A canonicalization error can, under certain conditions, cause IIS 4.0
or 5.0 to apply incorrect permissions to certain types of files. If
an affected file residing in a folder with restrictive permissions
were requested via a particular type of malformed URL, the
permissions actually used would be those of a folder in the file's
parentage chain, but not those of the folder the file actually
resides in. If the ancestor folder's permissions were more permissive
than those of the correct folder, the malicious user would gain
additional privileges to the affected file.
The vulnerability is subject to several significant restrictions:
- It only affects CGI scripts and file types that are implemented
via ISAPI extensions. It does not affect static web page or
non-web file types such as .exe, .doc or .bat
- It only affects servers that expose a web folder structure that
mirrors the physical folder structure on the server.
- It does not allow arbitrary permissions to be selected, only
permissions present on an ancestor folder
- It provides no way to enumerate the server and locate files that
could be affected by the vulnerability.
Affected Software Versions
- Microsoft Internet Information Server 4.0
- Microsoft Internet Information Server 5.0
- Microsoft Internet Information Server 4.0:
- Microsoft Internet Information Server 5.0:
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 MS00-057,
- Microsoft Knowledge Base article Q269862 discusses this issue and
will be available soon.
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Product Support Services is available at
Microsoft thanks Burt Abreu & SЬren Skov of VBExplorer.com for
reporting this issue to us and working with us to protect customers.
August 10, 2000: Bulletin Created.
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.
Last Updated August 10, 2000