__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Center ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Cisco - Multiple Vulnerabilities in ACL Implementations [Cisco Security Advisory: Revision 1.1] November 20, 2001 15:00 GMT Number M-018 ______________________________________________________________________________ PROBLEM: Six vulnerabilities involving Access Control List (ACL) has been discovered in multiple releases of Cisco IOSŪ Software Release for Cisco 12000 Series Internet Routers. PLATFORM: Cisco 12000 Series Internet Routers with line cards based on Engine 2 DAMAGE: Exploiting these vulnerabilities could result in Denial of Service attacks or allow some undesired traffic to pass into the protected network thus violating security policy. SOLUTION: Apply available patches or workarounds listed below. ______________________________________________________________________________ VULNERABILITY The risk is MEDIUM. Because of the range of vulnerabilities ASSESSMENT: listed in this advisory it is advisable to apply the patches as soon as possible. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/m-018.shtml ORIGINAL BULLETIN: http://www.cisco.com/warp/public/707/GSR-ACL-pub.shtml ______________________________________________________________________________ [***** Start Cisco Security Advisory: Revision 1.1 *****] Cisco Security Advisory: Multiple Vulnerabilities in Access Control List Implementation for Cisco 12000 Series Internet Router Revision 1.1 For Public Release 2001 November 14 08:00 (UTC -0800) Last Update 2001 November 15 12:00 (UTC -0800) Summary Six vulnerabilities involving Access Control List (ACL) has been discovered in multiple releases of Cisco IOSŪ Software Release for Cisco 12000 Series Internet Routers. Not all vulnerabilities are present in all IOS releases and only line cards based on the Engine 2 are affected by them. No other Cisco product is vulnerable. The workarounds are described in the Workarounds section. This advisory is available at http://www.cisco.com/warp/public/707/GSR-ACL-pub.shtml Affected Products Only Cisco 12000 Series Internet Routers with line cards based on Engine 2 are affected with these vulnerabilities. Not all line cards of a Cisco 12000 Series are affected by all vulnerabilities. Vulnerabilities are present in the underlying technology an individual line card is based upon. That technology is called "Engine". Currently Cisco is shipping line cards based on the following Engines: 0, 1, 2, 3 and 4. To determine what Engine your card is based on, you need to log on the Cisco 12000 router and issue "sh diag" command while in enable mode. The engine type will be displayed as "L3 Engine: x" where x will be the corresponding number. The following example shows the output for an Engine 2 based line card. c12000#sh diag SLOT 1 (RP/LC 1 ): 1 Port Packet Over SONET OC-48c/STM-16 Single Mode/SR SC-SC connector MAIN: type 41, 800-5271-01 rev A0 dev 0 HW config: 0x04 SW key: 00-00-00 PCA: 73-3295-05 rev A0 ver 5 HW version 1.1 S/N SDK034004AY MBUS: Embedded Agent Test hist: 0x00 RMA#: 00-00-00 RMA hist: 0x00 DIAG: Test count: 0x00000000 Test results: 0x00000000 L3 Engine: 2 - Backbone OC48 (2.5 Gbps) ^^^^^^^^^^^ <- Note the engine type [further output truncated] These vulnerabilities are affecting line cards based on Engine 2. Details Six vulnerabilities were found in IOS releases that are supporting Cisco 12000 platforms. Only line cards based on Engine 2 are affected. CSCdm44976 ACL will not block non initial fragments of a packet. This Cisco bug ID is adding a support for "fragment" keyword in the ACL. The White Paper Access Control Lists and IP Fragments describes how keyword fragment modifies behavior of ACL. CSCdu57417 The keyword "fragment" in the compiled ACL (Turbo ACL) is ignored if a packet is destined to the router itself. CSCdu03323 The implicit "deny ip any any" rule at the end of an ACL is ignored if an ACL of exactly 448 entries is applied on an interface as an outgoing ACL. An ACL with any other number of rules, greater or less than 448, is unaffected by this vulnerability. CSCdu35175 A support for "fragment" keyword in an outgoing ACL is added. Previously, only incoming ACL supported this keyword and outgoing ACL was ignoring it. CSCdt96370 An outbound Access Control List (ACL) may not block all intended traffic on a router when an input ACL is configured on some, but not all, interfaces of a multi port Engine 2 line card. The prerequisite is that, the traffic in question, was not filtered by an inbound ACL on the ingress port. An ACL applied at the ingress point will work as expected and block desired traffic. CSCdt69741 Packet fragments are not filtered by the ACL despite using "fragment" keyword. The White Paper Access Control Lists and IP Fragments describes how keyword fragment modifies behavior of ACL. Impact CSCdm44976 The router will not block all traffic. By sending an offending traffic in packet fragments it is possible to circumvent the protection offered by ACL and cause Denial-of-Service for the protected IP address. CSCdu57417 It is possible to cause the Denial-of-Service on the router itself if sufficient amount of traffic is sent to the router. This offending traffic should be send as packet fragments. CSCdu03323 If an outgoing ACL contains exactly 448 entries and if explicit rule "deny ip any any" is not present as the last statement, the ACL will fail to drop packets. Our tests shows that only 50% of packets are dropped. This may allow some undesired traffic to pass into the protected network thus violating security policy. CSCdu35175 Fragmented packets may be allowed into the protected network if the keyword "fragment" was applied to an outgoing ACL. CSCdt96370 This vulnerability can cause unwanted traffic to be allowed in and out of the protected network. The security based on an ACL will be breached completely. CSCdt69741 This vulnerability can be exploited to attack systems that are supposed to be protected by the ACL on the router. Software Versions and Fixes Each row of the table describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix and the anticipated date of availability for each are listed in the "Rebuild", "Interim", and "Maintenance" columns. A device running any release in the given train that is earlier than the release in a specific column (less than the earliest fixed release) is known to be vulnerable, and it should be upgraded at least to the indicated release or a later version (greater than the earliest fixed release label). When selecting a release, keep in mind the following definitions: Maintenance Most heavily tested and highly recommended release of any label in a given row of the table. Rebuild Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific defect. Although it receives less testing, it contains only the minimal changes necessary to effect the repair. Interim Built at regular intervals between maintenance releases and receives less testing. Interim releases should be selected only if there is no other suitable release that addresses the vulnerability, and interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available via manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco TAC. In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco TAC for assistance as shown in the following section. More information on Cisco IOS software release names and abbreviations is available at http://www.cisco.com/warp/public/620/1.html. Train Description of Image or Platform Availability of Fixed Releases* Vulnerability CSCdm4476 Rebuild Interim** Maintenance 12.0S Core/ISP support: GSR, RSP, c7200 12.0(10.1)S 12.0(11)S Vulnerability CSCdu57417 Rebuild Interim** Maintenance 12.0S Core/ISP support: GSR, RSP, c7200 12.0(19.3)S 12.0(19)S 12.0ST Early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 series routers for Service Providers (ISPs). 12.0(18.6)ST1 12.0(19.3)ST 12.0(19)ST Vulnerability CSCdu03323 Rebuild Interim** Maintenance 12.0S Core/ISP support: GSR, RSP, c7200 12.0(16)S2 12.0(17.5)S 12.0(17)S 12.0ST Early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 series routers for Service Providers (ISPs). 12.0(16.6)ST1 12.0(17.5)ST 12.0(17)ST Vulnerability CSCdu35175 Rebuild Interim** Maintenance 12.0S Core/ISP support: GSR, RSP, c7200 12.0(19.6)S 12.0ST Early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 series routers for Service Providers (ISPs). 12.0(19.6)ST Vulnerability CSCdt96370 Rebuild Interim** Maintenance 12.0S Core/ISP support: GSR, RSP, c7200 12.0(16)S1 12.0(17.1)S 12.0(17)S 12.0ST Cisco IOS software Release 12.OST is an early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 (GSR) series routers for Service Providers (ISPs). 12.0(15.6)ST3 12.0(17.1)ST 12.0(16)ST Vulnerability CSCdt69741 Rebuild Interim** Maintenance 12.0S Core/ISP support: GSR, RSP, c7200 12.0(16.6)S2 12.0(17.3)S 12.0(17)S 12.0ST Cisco IOS software Release 12.OST is an early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 (GSR) series routers for Service Providers (ISPs). 12.0(17.3)ST 12.0(18)ST Notes * All dates are estimates and subject to change. ** Interim releases are subjected to less rigorous testing than regular maintenance releases, and may have serious bugs. Obtaining Fixed Software Cisco is offering free software upgrades to eliminate this vulnerability for all affected customers. Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's Worldwide Web site at http://www.cisco.com. Customers whose Cisco products are provided or maintained through prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers should contact that support organization for assistance with the upgrade, which should be free of charge. Customers who purchase direct from Cisco but who do not hold a Cisco service contract and customers who purchase through third party vendors but are unsuccessful at obtaining fixed software through their point of sale should get their upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC contacts are as follows: +1 800 553 2447 (toll-free from within North America) +1 408 526 7209 (toll call from anywhere in the world) e-mail: tac@cisco.com Please have your product serial number available and give the URL of this notice as evidence of your entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC. Please do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades. Workarounds CSCddm44976 There is no direct workaround for this vulnerability. If feasible, packet fragments may be filtered before they reach the GSR. CSCdu57417 There is no direct workaround for this vulnerability. If feasible, packet fragments may be filtered before they reach the GSR. CSCdu03323 The workaround is to either shorten the ACL to be less than 448 lines in length or to explicitly add rule "deny ip any any" as the last statement. CSCdu35175 The workaround is to transform an ACL to an incoming ACL instead of the outgoing one. CSCdt96370 Apply an ACL on all ports on the ingress line card. If a particular port is supposed to not block any traffic, then apply the ACL of the form access-list xy permit ip any any. CSCdt69741 There is no direct workaround for this vulnerability. It is possible to block the fragments on an intermediate router, if such exists, that should be placed between the affected Cisco 12000 and the final target. The intermediate router must not be another Cisco 12000 affected by the same vulnerability. Exploitation and Public Announcements The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities described in this advisory. Status of This Notice: FINAL This is a final notice. Although Cisco cannot guarantee the accuracy of all statements in this notice, all of the facts have been checked to the best of our ability. Cisco does not anticipate issuing updated versions of this notice unless there is some material change in the facts. Should there be a significant change in the facts, Cisco may update this notice. A standalone copy or paraphrase of the text of this security advisory that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors. Distribution This notice will be posted on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/GSR-ACL-pub.shtml. In addition to Worldwide Web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients: cust-security-announce@cisco.com bugtraq@securityfocus.com first-teams@first.org (includes CERT/CC) cisco@spot.colorado.edu comp.dcom.sys.cisco firewalls@lists.gnac.com Various internal Cisco mailing lists Future updates of this notice, if any, will be placed on Cisco's Worldwide Web server, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the URL given above for any updates. Revision History Revision 1.0 2001-November-14 08:00 UTC -0800 Initial public release Revision 1.1 2001-November-15 12:00 UTC -08:00 Update table with fixed IOS releases Cisco Security Procedures Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/sec_incident_response.shtml. This includes instructions for press inquiries regarding Cisco security notices. All Cisco Security Advisories are available at http://www.cisco.com/go/psirt -------------------------------------------------------------------------------- This notice is Copyright 2001 by Cisco Systems, Inc. This notice may be redistributed freely after the release date given at the top of the text, provided that redistributed copies are complete and unmodified, and include all date and version information. [***** End Cisco Security Advisory: Revision 1.1 *****] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Cisco for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Center, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes 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: +1 925-422-8193 (7x24) FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@ciac.org Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ Anonymous FTP: ftp.ciac.org PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH 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 via WWW at http://www.first.org/. 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. 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