-----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ 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 21, 1995 16:00 GMT Number G-06A _________________________________________________________________________________ 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. - ----------------------------------------------------------------------------------- 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/mspwlupd.htm Update: http://www.microsoft.com/windows/download/mspwlupd.exe Copy the MSPWLUPD.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: http://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 _______________________________________________________________________________ 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. _______________________________________________________________________________ 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/vservupd.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. _______________________________________________________________________________ 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 worldwide. 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 E-mail: ciac@llnl.gov 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: http://ciac.llnl.gov/ Anonymous FTP: ciac.llnl.gov (128.115.19.53) Modem access: +1 (510) 423-4753 (14.4K baud) +1 (510) 423-3331 (14.4K baud) CIAC has several self-subscribing mailing lists for electronic publications: 1. CIAC-BULLETIN for Advisories, highest priority - time critical information and Bulletins, important computer security information; 2. CIAC-NOTES for Notes, a collection of computer security articles; 3. SPI-ANNOUNCE for official news about Security Profile Inspector (SPI) software updates, new features, distribution and availability; 4. SPI-NOTES, for discussion of problems and solutions regarding the use of SPI products. Our mailing lists are managed by a public domain software package called ListProcessor, which ignores E-mail header subject lines. 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A list of FIRST member organizations and their constituencies can be obtained by sending email to docserver@first.org with an empty subject line and a message body containing the line: send first-contacts. 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 -----BEGIN PGP SIGNATURE----- Version: 2.6.2 Comment: Processed by Mailcrypt 3.3, an Emacs/PGP interface iQCVAwUBMNnXfbnzJzdsy3QZAQFD8QP/WFglihiYrWXzHH7sFxXLnyk5qWD1AbGe /oIiZxPfMWz2RSDsYn9Jd2tftzVfCAXW0itz3eKM6b3R3Ce4RhVMkLU2yjw/4yVS fTTAlVuRC4X/lC+4z9lIenRxs5bHo16sf7KvjumIm4NhIzY9+EorP5CG1rd2oxhu OaRsCAS/JEw= =i2Xl -----END PGP SIGNATURE-----