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Permissions Problems with FrontPage Extensions
Permissions Problems with FrontPage Extensions Privacy and Legal Notice


K-048: Permissions Problems with FrontPage Extensions

June 2, 2000 14:00 GMT
PROBLEM:       Permission settings on FrontPage Extensions may allow
               defacements of web pages.
PLATFORM:      UNIX: The FrontPage Server Extensions on the following web
               servers: Apache 1.1.3 or 1.2, CERN 3.0, NCSA 1.5.2, Netscape
               Commerce Server 1.12, Netscape Communications Server 1.12,
               Netscape Enterprise 2.0 and 3.0, Netscape FastTrack 2.0.
               Windows NT: The FrontPage Server Extensions on the following
               web servers: Internet Information Server (IIS) 2.0 or higher,
               (including IIS 4.0), Netscape Commerce Server 1.12, Netscape
               Communications Server 1.12, Netscape Enterprise Server 2.0 and
               3.0, Netscape FastTrack 2.0, O'Reilly WebSite, FrontPage
               Personal Web Server.
               Windows 95/98: The FrontPage Extensions also run on Windows
               95/98, but this will be covered in a future bulletin.
DAMAGE:        A remote user may deface web pages of any given site when the
               permissions are not set properly.
SOLUTION:      Change the permissions on directories and files as indicated

VULNERABILITY The risk is HIGH. Multiple web pages have been defaced by ASSESSMENT: exploiting the permissions of FrontPage Extensions.
Over the last few weeks, the Federal community, including DOE, has seen a rash of web page defacements. Based on CIACís investigations into some of these incidents, intruders achieved access because the permissions on the Microsoft FrontPage Extensions had been inadvertently changed to allow an outsider to have "execute access" to the remote web authoring extension. TECHNICAL DETAILS: Windows NT: The Microsoft FrontPage server extensions may be installed automatically along with the Internet Information Server on a Windows NT Server. They are also used by other web management packages such as Visual InterDev. When they are installed automatically, the permissions are set to prevent outside access. However, if you are not careful you can inadvertently change the access permissions and allow any outsider to change a website. The site becomes vulnerable to attack when the users are given read execute (rx) access to the contents of the _vti_aut directory. This usually occurs when the site administrator sets the permissions on the webroot or _vti_bin directory and checks the check box "Replace permissions on subdirectories". This gives normal users execute access to the admin.dll and author.dll files. There are three extensions in each root web of a website. \webroot\_vti_bin\shtml.dll \webroot\_vti_bin\_vti_adm\admin.dll \webroot\_vti_bin\_vti_aut\author.dll The extension shtml.dll handles user interactions with web forms and must be accessible to the users of your website. The extension admin.dll controls administration of a website and must be restricted to site administrators. The extension author.dll allows remote authoring of web pages on the site and access must be restricted to administrators and only those authors who are allowed to change the web pages. The directory and file permissions on these files and directories should be as follows: _vti_bin users (rx)(rx), authors (rx)(rx), administrators (rx)(rx) _vti_adm administrators (rx)(rx) no user or author access _vti_aut authors (rx)(rx), administrators (rx)(rx) Here, users are the normal users of your web site including the web guest user IUSR_ if anonymous access is allowed. Authors are those people allowed to remotely change web pages and administrators are those users allowed to administer the web site. UNIX: Permissions on FrontPage Extensions on these systems are set in a similar manner as though mention for Windows NT. RECOMMENDATION: Web site managers who are using FrontPage to administer their sites should check these permissions to insure that only those who are allowed to author or administer the site have access to the admin.dll and author.dll extensions. Web site managers who are using IIS servers but not FrontPage should check for the existence of the FrontPage extensions (check for the _vti_* directories and for _vti_inf.html in the web root directory) and remove them if FrontPage is not required. OTHER IMPORTANT ISSUES: 1) Use care in tightening security through FrontPage Administrator. Itís easy to block access to everyone. 2) Test your permissions by attempting to edit your web page as a regular non-admin user. Put some character (like a dot) on the page and save it. If that character appears on the web page, you have a permission problem. Apply this method remotely to see if an outsider can modify the web page. If this works, then you still have a permission problem. 3) Make sure you set permissions correctly on all copies of _vti_bin and its subdirectories. There is one in each rootweb at a website. 4) Using scanners to identify this problem may not give you reliable results. For more information see:

CIAC services are available to DOE, DOE Contractors, and the NIH. CIAC can be contacted at:
    Voice:          +1 925-422-8193 (7 x 24)
    FAX:            +1 925-423-8002
    STU-III:        +1 925-423-2604
    World Wide Web:
                     (same machine -- either one will work)
    Anonymous FTP:
                     (same machine -- either one will work)

This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.
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