-------- From academic-firewalls-owner@net.tamu.edu Mon Jun 5 20:56:04 1995 X-Sender: swift@tamiya.llnl.gov Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Date: Mon, 5 Jun 1995 18:47:15 -0700 From: dwsmith@cheetah.llnl.gov (David Smith) (by way of uncl@llnl.gov (Frank Swift)) Reply-To: academic-firewalls@net.tamu.edu To: academic-firewalls@net.tamu.edu Subject: CIAC Bulletin F-25: Cisco Router IOS Soft. Vulnerability - -----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Cisco IOS Router Software Vulnerability June 2, 1995 1000 PDT Number F-25 _______________________________________________________________________________ PROBLEM: A vulnerability exists in Cisco's IOS software when the keyword 'established' is used with the extended IP access control list feature. This vulnerability can, under limited circumstances, allow unauthorized packets to circumvent a filtering router. This may permit unintended IP traffic to pass through a firewall setup. PLATFORM: IOS software levels: 10.3 (1) through 10.3 (2) 10.2 (1) through 10.2 (5) 10.0 (1) through 10.0 (9) DAMAGE: This vulnerability may permit unintended IP traffic to pass through a firewall setup. Networks protected from the firewall could be at risk and/or compromised. SOLUTION: Obtain and install the appropriate release of IOS software. AVAILABILITY: IOS software upgrades are available now. _______________________________________________________________________________ VULNERABILITY Due to the fact that unintended IP traffic may be able to ASSESSMENT: pass through a router used as part of a firewall, internal networks may be at risk and/or compromised. We urge all owners of Cisco routers that are configured to filter IP packets based upon the 'established' mechanism be upgraded as soon as possible. In addition, this problem may also exist in other vendors routers who support IP packet filtering and "extended access lists" features. We urge users who are using a router (configured with IP packet filtering and extended access list mechanisms) as part of a firewall, to contact their vendors to confirm that this vulnerability does not exist. _______________________________________________________________________________ CRITICAL Information for Cisco IOS Router Software CIAC has obtained information from Cisco, describing a vulnerability in Cisco's IOS software. Specific details of the vulnerability are provided in the included Cisco Security Advisory. [BEGINNING OF CISCO SECURITY ADVISORY] Cisco Security Advisory ----------------------- Thu Jun 1 16:27:08 PDT 1995 The following describes a vulnerability in Cisco's IOS software when the 'established' keyword is used in extended IP access control lists. This bug can, under very specific circumstances and only with certain IP host implementations, allow unauthorized packets to circumvent a filtering router. This vulnerability is present in the following IOS software versions: 10.3(1) through 10.3(2) 10.2(1) through 10.2(5) 10.0(1) through 10.0(9) and all previous versions of Cisco software. If you are running any of these IOS versions on a product that uses IP extended access lists, and you are using the 'established' keyword in these lists, then Cisco strongly recommends that you take immediate action to remove the vulnerability. You can determine what version of IOS you are running by issuing the following command: show version The recommended action is to upgrade to a more recent version of IOS, or take one of the immediate workaround actions described below. The vulnerability is fixed by in the following official software releases: 10.0(10) or later 10.2(6) or later 10.3(3) or later (For reference, the Cisco update identifier for this fix is "CSCdi34061".) Customers may obtain software upgrades without going through the Cisco's Technical Assistance Center via Cisco's Customer Information On-Line service, instructions for downloading are available at the end of this message. You may also contact your Cisco distributor or contact Cisco's Technical Assistance Center (TAC) for more information. TAC can be reached by phone at 800-553-2447, by E-Mail to tac@cisco.com or via the World-Wide-Web at http://www.cisco.com. In Europe you can contact TAC by phone at 32-2-778-42-42 or via E-Mail to euro-tac@cisco.com. - - - ---------------------------------------------------------------------------- A) Description A bug in Cisco's extended IP access list implementation can, under very specific circumstances, allow a user to bypass IP packet filtering. This may permit unintended IP traffic to pass through your firewall setup. To determine if you are vulnerable, look through your configuration. The configuration can be displayed by enabling and then entering the command "write term". If you see an access list line using a list number in the range of 100 through 199 that permits or denies TCP traffic and contains the word 'established' near the end of the line, you may be vulnerable. An example line might look like: In IOS 10.3: access-list 100 permit tcp any any established In IOS 10.2 or earlier: access-list 100 permit tcp 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255 established If you do not meet this test, then you are not vulnerable. You do not need to do anything. B) Workaround The following actions will remove the vulnerability: - Rewrite the access list parameters so the 'established' keyword is not necessary. This does not simply mean that you may remove the 'established' keyword, but rather that you will need to re-design your access lists to provide similar functionality without using the established mechanism. or - Disable the interfaces to which the access list is applied using the 'shutdown' interface subcommand: example: router(config)#interface ethernet 0 router(config-if)#shutdown C) Solution Obtain and install the appropriate release of IOS software as described above. For assistance contact Cisco's TAC. D) Technical Comments This problem is caused by an obscure but common design flaw, that we believe, exists in many router/firewall vendor's packet filtering implementations. Owners of non-Cisco hardware who use IP packet filtering features similar to Cisco's "extended access lists" as part of a firewall system may wish to contact their vendor to confirm that this vulnerability does not exist in their system. (Technical discussions about the problem have already occured in the appropriate forum.) This vulnerability can only be exploited with certain IP host implementations (we do not have information on which implementations are susceptible). Cisco suggests that all routers configured to filter IP packets based upon the 'established' mechanism be upgraded. - - - ---------------------------------------------------------------------------- Software upgrades may be obtained via any of the following mechanisms: A) World Wide Web (WWW): For registered CIO users please open a URL to: http://cio.cisco.com/kobayashi/Library_root.shtml and select the the version of software to download. For non-registered users open a URL to: http://cio.cisco.com/public/library/spc_req.shtml When prompted for a code, please enter: certjun2 for a list of available files to download. B) FTP: ftp cio.cisco.com and at the initial (username) prompt, enter: certjun2 At the password prompt, enter your e-mail address. Then: get README.certjun2 This file contains a list of files available that close this vulnerability. Please examine this list to determine which files you need and then download them. C) Character-based "CIO Classic": For access, the following connection options are offered: o telnet cio.cisco.com o Dial-up modem + In Europe +33 1 64 46 40 82 + In the US (408) 526 8070 + vt100, N81, up to 14.4Kbps Enter either as a guest or registered user and navigate to the topic: Software Updates Special Files At the prompt for a code, please enter: certjun2 A list of files will be displayed for you to select and download. - - - ---------------------------------------------------------------------------- [END OF CISCO SECURITY ADVISORY] _______________________________________________________________________________ CIAC wishes to thank Paul Traina of Cisco for the information provided in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy. 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 and DOE contractors, and CIAC can be contacted at: Voice: 510-422-8193 FAX: 510-423-8002 STU-III: 510-423-2604 E-mail: ciac@llnl.gov For emergencies and off-hour assistance, DOE and DOE contractor sites 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: (510) 423-4753 (14.4K baud) (510) 423-3331 (9600 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. To subscribe (add yourself) to one of our mailing lists, send the following request as the E-mail message body, substituting CIAC-BULLETIN, CIAC-NOTES, SPI-ANNOUNCE or SPI-NOTES for list-name and valid information for LastName FirstName and PhoneNumber when sending E-mail to ciac-listproc@llnl.gov: subscribe list-name LastName, FirstName PhoneNumber e.g., subscribe ciac-notes OUHara, Scarlett W. 404-555-1212 x36 You will receive an acknowledgment containing address, initial PIN, and information on how to change either of them, cancel your subscription, or get help. PLEASE NOTE: Many users outside of the DOE and ESnet 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 (FIRST) is a world-wide organization. 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. CIAC BULLETINS ISSUED IN FY95 (Previous bulletins available from CIAC) (F-01) SGI IRIX serial_ports Vulnerability (F-02) Summary of HP Security Bulletins (F-03) Restricted Distribution (F-04) Security Vulnerabilities in DECnet/OSI for OpenVMS (F-05) SCO Unix at, login, prwarn, sadc, and pt_chmod Patches Available (F-06) Novell UnixWare sadc, urestore, and suid_exec Vulnerabilities (F-07) New and Revised HP Bulletins (F-08) Internet Address Spoofing and Hijacked Session Attacks (F-09) Unix /bin/mail Vulnerabilities (F-10) HP-UX Remote Watch (F-11) Unix NCSA httpd Vulnerability (F-12) Kerberos Telnet Encryption Vulnerability (F-13) Unix sendmail vulnerabilities (F-14) HP-UX Malicious Code Sequences (F-15) HP-UX "at" and "cron" vulnerabilities (F-16) SGI IRIX Desktop Permissions Tool Vulnerability (F-17) Limited Distribution (F-18) MPE/iX Vulnerabilities (F-19) Protecting HP-UX Systems Against SATAN (F-20) Security Administrator Tool for Analyzing Networks (SATAN) (F-21) Protecting SUN OS Systems Against SATAN (F-22) SATAN Password Disclosure (F-23) Protecting IBM AIX Systems Against SATAN (F-24) Protecting SGI IRIX Systems Against SATAN CIAC NOTES ISSUED IN FY1995 (Previous Notes available from CIAC) 04c December 8, 1994 05d January 11, 1995 06 March 22, 1995 07 March 29, 1995 08 April 4, 1995 09 April 24, 1995 - -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBL9OFtrnzJzdsy3QZAQHcCQP/dd0ux2XD8U/KDroOitlzuiD+nfgf7huR vNQzqe/TdZVrvKXSNQDeo2IOv+m+8Tm5vxI/T90Ygc4hTcvUGZX0AZj29CjptQ1K ULmKs3SVbPIjINR+maDiv8wF6se0vufWDGgblEtCasobPZNEVTaUS1V7o0BD7ikP mkwC54bGByw= =ECGp - -----END PGP SIGNATURE-----