g-06.Win95.Vulnerability.asc
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The U.S. Department of Energy
Computer Incident Advisory Capability
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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.
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1. PASSWORD CACHE VULNERABILITY
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.
_______________________________________________________________________________
PROBLEM
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
services.
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.
_______________________________________________________________________________
SOLUTION
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:
Description:
http://www.microsoft.com/windows/software/mspwlupt.htm
Update:
http://www.microsoft.com/windows/download/mspwlupt.exe
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
in:
html://www.microsoft.com/windows/software/admintools.htm
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.
===============================================================================
2. FILE SHARING/REMOTE ADMINISTRATION VULNERABILITY
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PROBLEM
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.
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SOLUTION
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:
Descriptions:
http://www.microsoft.com/windows/software/w95fpup.htm
File and Printer Sharing for NetWare Networks driver:
http://www.microsoft.com/windows/download/nwsrvupd.exe
File and Printer Sharing for Microsoft Networks driver:
http://www.microsoft.com/windows/download/uservupd.exe
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.
_______________________________________________________________________________
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