************************************************************************** Security Bulletin 9524 DISA Defense Communications System June 6, 1995 Published by: DDN Security Coordination Center (SCC@NIC.DDN.MIL) 1-(800) 365-3642 DEFENSE DATA NETWORK SECURITY BULLETIN The DDN SECURITY BULLETIN is distributed by the DDN SCC (Security Coordination Center) under DISA contract as a means of communicating information on network and host security exposures, fixes, and concerns to security and management personnel at DDN facilities. Back issues may be obtained via FTP (or Kermit) from NIC.DDN.MIL [192.112.36.5] using login="anonymous" and password="guest". The bulletin pathname is scc/ddn-security-yynn (where "yy" is the year the bulletin is issued and "nn" is a bulletin number, e.g. scc/ddn-security-9428). ************************************************************************** + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + ! ! ! The following important advisory was issued by the Automated ! ! Systems Security Incident Support Team (ASSIST) and is being ! ! relayed unedited via the Defense Information Systems Agency's ! ! Security Coordination Center distribution system as a means ! ! of providing DDN subscribers with useful security information. ! ! ! + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Automated Systems Security Incident Support Team _____ ___ ___ _____ ___ _____ | / /\ / \ / \ | / \ | | / Integritas / \ \___ \___ | \___ | | < et /____\ \ \ | \ | | \ Celeritas / \ \___/ \___/ __|__ \___/ | |_____\ <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Bulletin 95-22 Release date: 6 June, 1995, 11:15 AM EDT (GMT -4) SUBJECT: Vulnerability in Cisco's IOS software. SUMMARY: Some versions of Cisco's IOS software contain a vulnerability when the 'established' keyword is used in extended IP access control lists. The vulnerability could allow a user to bypass IP packet filtering. The Cisco update identifier for this fix is CSCdi34061. BACKGROUND: The following IOS versions are affected: 10.3(1) through 10.3(2) 10.2(1) through 10.2(5) 10.0(1) through 10.0(9) and all versions of Cisco software previous to 10.0. You can determine what version of IOS you are running by issuing the following command: show version To determine if your IOS configuration is vulnerable issue the following command to display configuration parameters: 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 and no further action is required. The vulnerability is fixed in the following official Cisco software releases: 10.0(10) or later 10.2(6) or later 10.3(3) or later IMPACT: This bug can, under very specific circumstances and only with certain IP host implementations, allow unauthorized packets to circumvent a filtering router. RECOMMENDED SOLUTIONS: Determine whether or not Cisco systems at your site are vulnerable and take action to correct the problem on all systems that are vulnerable. 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 information from Cisco are included later in 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. Temporary 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 Permanent Fix Obtain and install the appropriate updated release of IOS software that has the problem fixed (see BACKGROUND section above). For assistance contact Cisco's TAC. Technical Comments This problem is caused by an obscure but common design flaw that may exist in other vendor's router/firewall 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. This vulnerability can only be exploited with certain IP host implementations (the Cisco Security Bulletin on this topic did not have information on which implementations are susceptible). Obtaining Cisco software upgrades. A. World Wide Web (WWW): Registered CIO users can open a URL to: http://cio.cisco.com/kobayashi/Library_root.shtml and select the the version of software to download. Non-registered users can open a URL to: http://cio.cisco.com/public/library/spc_req.shtml When prompted for a code, 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. C. Character-based "CIO Classic": For access, the following connection options are offered: 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. ASSIST would like to thank the Cisco Corporation for information contained in this bulletin. <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> ASSIST is an element of the Defense Information Systems Agency (DISA), Center for Information Systems Security (CISS), that provides service to the entire DoD community. Constituents of the DoD with questions about ASSIST or computer security security issues, can contact ASSIST using one of the methods listed below. Non-DoD organizations/institutions, contact the Forum of Incident Response and Security Teams (FIRST) (FIRST) representative. To obtain a list of FIRST member organizations and their constituencies send an email to docserver@first.org with an empty "subject" line and a message body containing the line "send first-contacts". ASSIST Information Resources: To be included in the distribution list for the ASSIST bulletins, send your Milnet (Internet) e-mail address to assist-request@assist.mil. Back issues of ASSIST bulletins, and other security related information, are available from the ASSIST BBS at 703-607-4710, DSN 327-4710 and through anonymous FTP from assist.mil (IP address 199.211.123.11). Note: assist.mil will only accept anonymous FTP connections from Milnet addresses that are registered with the NIC or DNS. If your system is not registered, you must provide your MILNET IP address to ASSIST before access can be provided. ASSIST Contact Information: PHONE: 800-357-4231 (or 703-756-7974 DSN 289), duty hours are 06:00 to 22:30 EDT (GMT -4) Monday through Friday. During off duty hours, weekends and holidays, ASSIST can be reached via pager at 800-791- 4857. The page will be answered within 30 minutes, however if a quicker response is required, prefix the phone number with "999". ELECTRONIC MAIL: Send to assist@assist.mil. ASSIST BBS: Leave a message for the "sysop". Reference herein to any specific commercial product, process, or service by trade name, trademark manufacturer, or otherwise, does not constitute or imply its endorsement, recommendation, or favoring by ASSIST. The views and opinions of authors expressed herein shall not be used for advertising or product endorsement purposes. **************************************************************************** * * * The point of contact for MILNET security-related incidents is the * * Security Coordination Center (SCC). * * * * E-mail address: SCC@NIC.DDN.MIL * * * * Telephone: 1-(800)-365-3642 * * * * NIC Help Desk personnel are available from 7:00 a.m.-7:00 p.m. EST, * * Monday through Friday except on federal holidays. * * * **************************************************************************** PLEASE NOTE: Some users outside of the DOD computing communities may receive DDN Security bulletins. If you are not part of the DOD community, please contact your agency's incident response team to report incidents. Your agency's team will coordinate with DOD. 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 service to the DOD community. Neither the United States Government nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, 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. The opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government, and shall not be used for advertising or product endorsement purposes.