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@stake Advisory: SiteMinder Access Control Bypass (A0911 00-1)
From: "@stake Advisories" <advisories () ATSTAKE COM>
Date: Mon, 11 Sep 2000 08:53:52 -0400

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                               @stake Inc.
                            www.atstake.com

                           Security Advisory

Advisory Name: SiteMinder Access Control Bypass (A091100-1)
 Release Date: 09/11/2000
  Application: Netegrity SiteMinder 3.6, 4.0
     Platform: Solaris 2.x, Windows NT
     Severity: Access control mechanism can be bypassed
      Authors: David Litchfield (dlitchfield () atstake com)
               Mark Litchfield (mlitchfield () atstake com)
 Contributors: Frank Swiderski (fes () atstake com)
Vendor Status: Vendor has released a patch
          Web: www.atstake.com/research/advisories/2000/a091100-1.txt


Overview:
                
Netegrity's SiteMinder
(http://www.netegrity.com/products/siteminder.html) is a web access
control product for Solaris and Windows NT that implements various
authentication mechanisms to protect content on websites.  It
features native integration with industry-standard LDAP, NDS, and
NT directory services as well as SQL databases.

SiteMinder supports more fine-grained access control than is
normally provided by web servers.  For example, user access can be
restricted to the level of buttons or form fields whereas web servers
generally restrict access at the page level.

Due to an error in SiteMinder's URL parsing, it is possible for
an attacker to bypass the authentication phase and view protected web
pages directly.


Detailed Description:

SiteMinder's authentication mechanism can be bypassed by using
a properly crafted URL.  For example, assume the following web page
is protected:
        
 http://www.mysite.com/cgi-bin/secrets.html

Normally, if someone were to try accessing this page, SiteMinder
would intercept the request and prompt for a username and password
before allowing the user to execute the script and view the results.
However, the user can make a small modification to the URL to avoid
the authentication phase:

 http://www.mysite.com/cgi-bin/secrets.html/$/foo.ccc

When using a URL crafted in this manner, SiteMinder appears to
ignore its access control policy and simply allows the requested page
to be served to the attacker with no further prompting.

This vulnerability can be used not only to view static web pages,
but also to execute CGI applications and to view server-side source
code.  Again, all of these actions can be performed without ever
being prompted for authorization.  Example URLs are as follows:

To execute a CGI application:

 http://www.mysite.com/cgi-bin/restricted.cgi$/foo.ccc?subject=blah
        
To view the source code for that CGI application:

 http://www.mysite.com/cgi-bin/restricted.cgi/$/foo.ccc

To execute a servlet:
        
 http://www.mysite.com/applets/restricted/$/foo.ccc?query=blah


In the example URL, the non-existent file "foo.ccc" is used
after the "$/" delimiter; however, any filename can be used here
provided it has an extension of .ccc, .class, or .jpg (and possibly
others that have not yet been discovered).


Vendor Response (received via email from Netegrity):

Netegrity identified and fixed this issue earlier this year. The
issue does not exist in the currently shipping SiteMinder 4.11
product, which has already been distributed to all customers on
maintenance. Customers using previous versions of SiteMinder have
been notified of the issue and alerted that they can download the
patch from the customer support section of the Netegrity web site.
Customers can also call customer service at 800-325-9870 with any
questions or concerns.


Recommendations:

First install the vendor patch.  The patch does *not* fix the
protection of URLs that do not have a file extensions which is
commonly the case for CGI programs and servlets. An example is the
following:

 http://www.mysite.com/applets/restricted

In this case add a file extension so that the patch will work.

 http://www.mysite.com/applets/restricted.applet



For more advisories: http://www.atstake.com/research/index.html
PGP Key: http://www.atstake.com/research/pgp_key.asc

Copyright 2000 @stake, Inc. All rights reserved.


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