-----BEGIN PGP SIGNED MESSAGE----- <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 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". ASSIST uses Pretty Good Privacy (PGP) 2.6.2 as the digital signature mechanism for bulletins. PGP 2.6.2 incorporates the RSAREF(tm) Cryptographic Toolkit under license from RSA Data Security, Inc. A copy of that license is available via anonymous FTP from net-dist.mit.edu (IP 18.72.0.3) in the file /pub/PGP/rsalicen.txt. In accordance with the terms of that license, PGP 2.6.2 may be used for non-commercial purposes only. Instructions for downloading the PGP 2.6.2 software can also be obtained from net-dist.mit.edu in the pub/PGP/README file. PGP 2.6.2 and RSAREF may be subject to the export control laws of the United States of America as implemented by the United States Department of State Office of Defense Trade Controls. The PGP signature information will be attached to the end of ASSIST bulletins. 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. - -----BEGIN PGP PUBLIC KEY BLOCK----- Version: 2.6 mQCNAi4uZ40AAAEEAM1uraimCNeh5PtzX7KoGxC2u8uMTdl8V5sujk3MHbWvCuOM W0FqDy5s9iwfQLZWzJ7cbM6L0mNOj8eJGoz7TqGKZDDRFlKAwg0x8joleZLC2gXw FVdF/g6Mdv7ok7heoa+Y//YMeADnsSrmzqLCnhFbKYffww3EbdH6sbnW3Io9AAUR tB9BU1NJU1QgVGVhbSA8YXNzaXN0QGFzc2lzdC5taWw+iQCVAwUQL1xx7tH6sbnW 3Io9AQEBYwP9FvIJbnKjtMLUj8ghd6hophSx8WZnfQsOmZX/BbX8vKz1a5BkBn4q ANvW+uKGdUlE8LLMEm1PD59Cihcb3OoWDOU8zIOIErvry4eqa+LzEXV8nnBdes+A a1MCMGSz+K3OaP78lQ7JCGoY9TXTWIelfAdBVBG4VQcSQRn8tjRdG2e0KEFTU0lT VCBUZWFtIDxhc3Npc3RAYXNzaXN0Lmltcy5kaXNhLm1pbD6JAJUCBRAuLnHoh0Y9 0jC+b6kBAU0TA/4yXSL7K6tcfVm9ACnP4crCoutFM2w10e7YKxD850ajhWrh6rI9 O+sjU5WObqiPJ7sZHdEw/KARzPSijH/5h8HlyYa6ClksWxYuymzCsUYYJctdjcGr uakfXgYQ1TkkyUfNrN5G90NuRK/vTRe7bkmyGNYjN9Njac1Q18WVF59Chg== =d5rP - -----END PGP PUBLIC KEY BLOCK----- -----BEGIN PGP SIGNATURE----- Version: 2.6 iQCVAwUBL9Rx59H6sbnW3Io9AQGUEwP/RW6LmpGcOLBIBjZMEN3mpA6+7Ouypjl+ eYO1kTFpRB8iPM14+Aoyq8+7jeoKUDNmFL2fVcbUBgoJgIu5PKeOtBh6IHzYOpQA w0pb0ZoobjGcdDGLfqMKjnkZB+mSJHN3f11MLXWthtwA2luy3tnQ8Xg2GwMdHXIF aSi+fELpPjc= =irIN -----END PGP SIGNATURE-----