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TUCoPS :: Windows :: ciacg006.txt

Win95 Vulnerability



                       The U.S. Department of Energy
                    Computer Incident Advisory Capability
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___

                             INFORMATION BULLETIN

                            Win95 Vulnerabilities

       This bulletin describes two unrelated vulnerabilities in Windows 95.
             1. The password cache vulnerability.
             2. The file sharing/remote administration vulnerability.

December 18, 1995 18:00 GMT                                        Number G-06

PROBLEM:     1. A weak encryption algorithm allows the password cache to be 
                decrypted and read.
             2. A problem in the file sharing/remote administration facility gives 
                administrative access on a Win 95 machine to unauthorized users.
PLATFORM:       Windows 95
DAMAGE:      1. Anyone who can obtain a copy of the Windows 95 password cache could
                obtain usernames and passwords for all of a user's password 
                protected services, including passwords for logins to remote 
                systems and file servers.
             2. Network users may obtain read only access to a machine.
SOLUTION:       Apply replacement modules from Microsoft.
- -----------------------------------------------------------------------------------
VULNERABILITY 1. The password cache vulnerability allows an intruder who can obtain 
ASSESSMENT:      a copy of the password cache file to gain access to any remote 
                 systems and servers that the user had access to. 
              2. The file and printer sharing vulnerability only affects those 
                 systems where file sharing and remote administration are enabled 
                 and the administrator has logged in and logged off. Rebooting the
                 machine sets the access back to normal.
- -----------------------------------------------------------------------------------


The password cache on a Windows 95 system is designed to simplify network access for 
a user by storing the encrypted passwords needed to access the user's network 
services. Network services include Netware and Windows Network servers, printer 
servers, and connections to network service providers such as the Microsoft Network. 
After the user unlocks the cache with a single password, all future passwords are 
automatically obtained from the cache. 

The encryption mechanism used to protect the Windows 95 password cache is weak and 
is easily broken by anyone with access to the cache files. Once the encryption is 
broken, an intruder has all the usernames and passwords for all of a user's network 

Note that to exploit this vulnerability, an intruder must be able to obtain a copy 
of the password cache file. To obtain a copy, he must have physical access to the 
machine, or the file must be in a shared directory that the intruder can read.

On December 13, 1995, Microsoft released a security update to correct this problem. 
Obtain the security update from Microsoft and install it on your system. The 
security enhancement increases the encryption key from 32 to 128 bits, significantly 
improving the protection of the password cache file. The security update is 
available at the Microsoft WWW site in:


Copy the MSPWLUPT.EXE file to a directory on a Windows 95 machine and run it. The 
update program automatically updates your password file to the new format and 
installs MSPWL32.DLL and NET.EXE. If you have turned off password caching using the 
Policy Editor, the updater program gives you the option to turn it back on. The 
operation of NET.EXE is also changed by this update. NET.EXE, which is usually used 
from the command line, will no longer use the password cache. Users will be prompted 
for passwords whenever they use NET.EXE.

In addition to patching the files, you should insure that strong passwords are used 
to secure the cache file. A password policy can be enforced by using the policy 
editor to set the minimum password length and force the password to be alphanumeric. 
The policy editor is available on the Windows 95 CD-ROM (not on the floppy disk 
version) in \admin\apptools\poledit. It is also available at the Microsoft WWW site 


Instructions for installing the policy editor come with the tool.

Another useful tool is the Password Cache Editor. This editor lets you edit a 
password cache file and remove any passwords that do not need to be stored in it.
The password editor is available in the "Microsoft Windows 95 Resource Kit" or at 
the same location as the policy editor at the Microsoft WWW site.




There are two separate problems with the file and printer sharing capability. 

First, for the network client driver "File and Printer Sharing for NetWare 
Networks" an intruder can obtain read access to the files on a user's machine. To be 
at risk, a system:

  1. Must be configured to share files and printers with other users on the
     network using the "File and Printer Sharing for NetWare Networks" client.
  2. Must have remote administration enabled or have installed 
     Microsoft Remote Registry Services.
  3. The administrator must have logged on and logged off of the machine.

Any machine with the configuration above is at risk until it is rebooted.

Second, for the network client driver "File and Printer Sharing for Microsoft 
Networks" a problem exists with the Samba network client running on a UNIX system, 
that may allow file access by intruders on the local network or on the Internet. To 
be at risk, a system:

  1. Must be configured to share files and printers with other users on the 
     network using the "File and Printer Sharing for Microsoft Networks" client.
  2. Must share a LAN, Internet, or Dial-Up connection with a UNIX-based
     computer running Samba's SMBCLIENT software.
  3. Must not have peer services disabled using System Policies.

Any machine with the configuration above is at risk from machines using Samba's 
network client. 


On October 20, 1995, Microsoft made the following two updated network client drivers 
available to correct these problems:

        File and Printer Sharing for NetWare Networks
        File and Printer Sharing for Microsoft Networks

The drivers are available from the Microsoft WWW server:


File and Printer Sharing for NetWare Networks driver:

File and Printer Sharing for Microsoft Networks driver:

Both drivers are also available from The Microsoft Network online service, and have 
been made available to other online services including CompuServe, America Online, 
and Prodigy. The updated drivers will also be mailed to any user free of charge if 
they call Microsoft's FastTips line, 800/936-4200.

To install the new drivers, insert the driver installer files in a directory on the 
Windows 95 machine and run them. The new drivers are automatically installed in your 
Windows 95 system.


CIAC wishes to acknowledge the contributions of DOD ASSIST and Microsoft for the 
information contained in this bulletin.

CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy (DOE) and the 
National Institute of Health (NIH). CIAC is located at the Lawrence Livermore 
National Laboratory in Livermore, California. CIAC is also a founding member of 
FIRST, the Forum of Incident Response and Security Teams, a global organization
established to foster cooperation and coordination among computer security teams 

CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be 
contacted at:
    Voice:    +1 510-422-8193
    FAX:      +1 510-423-8002
    STU-III:  +1 510-423-2604

For emergencies and off-hour assistance, DOE, DOE contractor sites, and the NIH 
may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), call the CIAC 
voice number 510-422-8193 and leave a message, or call 800-759-7243 
(800-SKY-PAGE) to send a Sky Page. CIAC has two Sky Page PIN numbers, the 
primary PIN number, 8550070, is for the CIAC duty person, and the secondary 
PIN number, 8550074 is for the CIAC Project Leader.

Previous CIAC notices, anti-virus software, and other information are 
available from the CIAC Computer Security Archive. 

   World Wide Web:
   Anonymous FTP: (
   Modem access:        +1 (510) 423-4753 (14.4K baud)
                        +1 (510) 423-3331 (14.4K baud)

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PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities
receive CIAC bulletins.  If you are not part of these communities, please
contact your agency's response team to report incidents. Your agency's team
will coordinate with CIAC. The Forum of Incident Response and Security Teams
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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.

LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC)

(F-24)  Protecting SGI IRIX Systems Against SATAN
(F-25)  Cisco IOS Router Software Vulnerability
(F-26)  OSF/DCE Security Hole
(F-27)  Incorrect Permissions on /tmp
(F-28)  Vulnerability in SunOS 4.1.* Sendmail (-oR option)
(G-1)   Telnetd Vulnerability
(G-2)   SunOS 4.1.X Loadmodule Vulnerability
(G-3)   AOLGOLD Trojan Program
(G-4)   X Authentication Vulnerability
(G-5)   HP-UX FTP Vulnerability Bulletin

RECENT CIAC NOTES ISSUED (Previous Notes available from CIAC)

Notes 07 - 3/29/95   A comprehensive review of SATAN

Notes 08 - 4/4/95    A Courtney update

Notes 09 - 4/24/95   More on the "Good Times" virus urban legend

Notes 10 - 6/16/95   PKZ300B Trojan, Logdaemon/FreeBSD, vulnerability
                     in S/Key, EBOLA Virus Hoax, and Caibua Virus

Notes 11 - 7/31/95   Virus Update, Hats Off to Administrators,
                     America On-Line Virus Scare, SPI 3.2.2 Released, 
                     The Die_Hard Virus

Notes 12 - 9/12/95   Securely configuring Public Telnet Services, X Windows, 
                     beta release of Merlin, Microsoft Word Macro Viruses,
                     Allegations of Inappropriate Data Collection in Win95

Version: 2.6.2
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