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computer-security/Windows NT Security FAQ


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Archive-name: computer-security/ntsecurity
Posting-frequency: monthly
Last-modified: 1999/9/11
Version: 3.00

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Windows NT Security FAQ

Version: 3.00
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This Security FAQ is a resource provided by:

     Internet Security Systems, Inc.
     Suite 660, 41 Perimeter Center East          Tel: (770) 395-0150
     Atlanta, Georgia 30346                       Fax: (770) 395-1972

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To get the newest updates of Security files check the following services:

     http://www.iss.net/
     ftp ftp.iss.net /pub/

To subscibe to the update mailing list, Alert, send an e-mail to
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line), write:

     subscribe alert

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The NT environment allows the security to be very flexible. For an
administrator, they should be aware of the issues for having a secure NT
machine. Here are some of the major security issues.

   * NT Security Mailing List
   * Access control lists (ACLs)
   * Network Access
   * Registry
   * PPTP (Point to Point Tunneling Protocal)
   * File Shares
   * MS IIS Web Server
   * FTP Server
   * NFS Server
   * Rsh Server
   * Additional NT Security Info

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NT Security Mailing List

To join, send e-mail to request-ntsecurity@iss.net and, in the text of your
message (not the subject line), write:

        subscribe ntsecurity

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Access control lists

To really lock NT down hard, set the root directory to full access for
administrators and system, list access to users (not Everyone). Let that
work all the way down the tree. Loosen things up as need be, but what has
been done is ensure that any new directory that gets created will have those
permissions.

Make sure the print spool directory has full access to creator\owner (see
the NT Resource Kit, 3.51 Update 1 (also known as vol 5)).

Go through (using cacls, or use the search facility of either file manager
or explorer) and set the permissions on all of the executables and DLLs to
full access to admins (or if people normally work on that machine under
admin status, remove write permission for admins), and list only
(read-execute) permissions to users.

Note that it is now difficult for users to install any software. This could
be good or bad, depending on what you want to do. Make a list of common DLLs
that are updated often and give users delete permission.

Now apply the "smoke test" - log in as a user, and see what is broken. Some
programs insist on being able to write to an .ini file in the system tree -
if users can't write to (or create) these files, these programs will fail.
Change the permissions as need be.

Be careful, it is possible where non-admins either can't successfully log
in, or get a desktop that is completely blank.

If users are allowed to store files locally, make sure that they have full
rights to their own directories. Note that under NT 4.0, a user's desktop
profile, and numerous other things are stored under the system tree - look
in %systemroot%\profiles, and make sure each user has full rights to their
subdirectory - it should be admin, system, and user have full access.

It is a good idea to loosen up the temp directory - a good thing is to give
users list access, but creator\owner full access. There may be other
directories that need work, depending on what apps are installed, and
whether they have any notion of multiple users - one example would be the
cache directory for a web browser.

Since people have a lot of different needs, there is no single answer - it
depends on the environment.

As to user rights, go through and make sure Guest is not only disabled, but
that it has no rights to anything.

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Network Access

Give careful attention to who is allowed to log on from the network and
locally.

One thing to consider is that the administrator account is on every machine,
and can't be locked out from too many bad passwords. A good way around this
is to remove the administrator's group from the permissions to log on from
the network, and add back in the individual users who are the admins.

Now go set it up to audit failed login attempts, lock out users for a few
minutes if there are too many login failures, and require a password of
decent length - 6 characters is acceptable. This makes brute force attacks
very difficult. If you want to prevent other users from accessing the
machine remotely, you can also remove the users from the right to log on
from the network - that confines the users to having to use the shares on
the server. This also prevents anyone not given that right from accessing
the event log, the registry, and the shares on the machine. Pay attention to
who can and cannot shut the machine down, and make it require you to log in
to shut it down.

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PPTP

Point to Point Tunneling Protocal

This is a feature in NT 4.0 that allows encryption between an NT 4.0 server
and possible dialins. There is source code available on
http://www.microsoft.com. There are several companies that provide dialin
access such as US Robotics that is adding in support for PPTP.

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Registry

In the registry, Remove write permission to Everyone from HKEY_CLASSES_ROOT,
and give full access to creator\owner, which is what Microsoft did with NT
4.0 - much more secure.

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File Shares

Go through all the shares that are available and make sure that the
permissions are set correctly - don't accept the default of full access to
everyone.

The file sharing service if available and accessible by anyone can crash the
NT 3.51 machine by using the dot..dot bug and require it to be rebooted.
This technique on a Windows 95 machine potentially allows anyone to gain
access to the whole hard drive. This vulnerability is documented in
Microsoft Knowledge Base article number Q140818 last revision dated March
15, 1996. Resolution is to install the latest service pack for Windows NT
version 3.51. The latest service pack to have the patch is in service pack
4.

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MicroSoft IIS Web Server

Versions prior to 1.0c were vulnerable to allowing users to execute commands
remotely and allow access to all the files on the same hard drive partition
as the IIS Server. Make sure that the web server is version 1.0c or higher.
NT 4.0 comes with IIS Version 2.0 that fixes these known problems.

Additonal Information on the IIS Web Server bugs is available at
http://www.omna.com/msiis .

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FTP Server

Many times FTP is configured to allow anyone to log in and have access to
the whole hard drive. Attempt to log in and check to see what files are
accessible. By doing a "cd ..", it may allow people to go higher in the file
system that what is intended.

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NFS Server

Network File System can easily be configured to allow anyone to have access
to files being exported. Check to see if they are correctly configured for
the proper exports.

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Rsh Server

There is an rsh server that comes with NT. Rsh is a service that allows
people to configure their login to not require a password if coming from
certain machines. Intruders have figured out ways to by-pass this security
and it is recommended to not allow this server to run.

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Additional NT Security Info

Here are two other great resources of NT Security Information:

   * http://www.ntshop.net/security/ntexploits.htm
   * http://www.it.kth.se/~rom/ntsec.html

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Copyright

This paper is Copyright (c) 1994, 1995, 1996
   by Christopher Klaus of Internet Security Systems, Inc.

Permission is hereby granted to give away free copies electronically. You
may distribute, transfer, or spread this paper electronically. You may not
pretend that you wrote it. This copyright notice must be maintained in any
copy made. If you wish to reprint the whole or any part of this paper in any
other medium excluding electronic medium, please ask the author for
permission.

Disclaimer

The information within this paper may change without notice. Use of this
information constitutes acceptance for use in an AS IS condition. There are
NO warranties with regard to this information. In no event shall the author
be liable for any damages whatsoever arising out of or in connection with
the use or spread of this information. Any use of this information is at the
user's own risk.

Address of Author

Please send suggestions, updates, and comments to:
Christopher Klaus <cklaus@iss.net> of Internet Security Systems, Inc.
<iss@iss.net>

Internet Security Systems, Inc.

ISS is the leader in network security tools and technology through
innovative audit, correction, and monitoring software. The Atlanta-based
company's flagship product, Internet Scanner, is the leading commercial
attack simulation and security audit tool. The Internet Scanner SAFEsuite is
based upon ISS' award-winning Internet Scanner and was specifically designed
with expanded capabilities to assess a variety of network security issues
confronting web sites, firewalls, servers and workstations. The Internet
Scanner SAFEsuite is the most comprehensive security assessment tool
available. For more information about ISS or its products, contact the
company at (770) 395-0150 or e-mail at iss@iss.net. ISS maintains a Home
Page on the World Wide Web at http://www.iss.net
-- 
Christopher William Klaus            Voice: (770)395-0150. Fax: (770)395-1972
Internet Security Systems, Inc.              "Internet Scanner SAFEsuite finds
Ste. 660,41 Perimeter Center East,Atlanta,GA 30346 your network security holes
Web: http://www.iss.net/  Email: cklaus@iss.net        before the hackers do."

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