-----BEGIN PGP SIGNED MESSAGE----- Cisco Security Advisory: Data Leak with Cisco Express Forwarding Enabled Revision 1.0 For Public Release 2002 February 27 08:00 (UTC -0800) - -------------------------------------------------------------------------- Summary ======= All Cisco devices running Cisco IOS® and having Cisco Express Forwarding (CEF) enabled can leak information from previous packets that have been handled by the device. This can happen if the packet length described in the IP header is bigger than the physical packet size. Packets like these will be expanded to fit the IP length and, during that expansion, an information leak may occur. Please note that an attacker can only collect parts of some packets but not the whole session. No other Cisco product is vulnerable. Devices that are having fast switching enabled are not affected by this vulnerability. The workaround for this vulnerability is to disable CEF. This advisory is available at the http://www.cisco.com/warp/public/707/ IOS-CEF-pub.shtml. Affected Products ================= All Cisco IOS releases that are supporting CEF are vulnerable. In order to trigger this vulnerability CEF or dCEF must be enabled on the device. The vulnerable Cisco IOS releases are (this is not an exhaustive list): * 11.1CC * 12.0, 12.0S, 12.0T, 12.0ST * 12.1, 12.1E, 12.1T * 12.2, 12.2T No other Cisco products are affected. Details ======= When a router receives a packet where MAC level packet length is shorter than is indicated by the IP level, the router will "extend" the packet to the size indicated by the IP level. This extension will be done by padding the packet with an arbitrary data. The issue here is that padding may contain data from a previous packets that has not been erased. Although it is possible to trigger this vulnerability on command, it is not possible to predict what information would be collected this way. It is not possible for an attacker to selectively capture desired packets (for example, packets with username and password combination). This vulnerability is specific to CEF. Fast switching is not affected by it. This vulnerability is documented as Cisco Bug ID CSCdu20643. For the Cisco IOS 11.1CC image, this vulnerability is described as Cisco Bug ID CSCdp58360. Impact ====== By sending malformed packets, and capturing them after they have been processed by CEF, an attacker may find a remnants of a previous packets in them. The remnant data may contain whatever the previous packet has carried. That may be parts of a document, mail or any other content. Note that in an interactive session such as typing a password, characters are sent one by one in separate packets. That drastically lowers the probability that all packets will be captured. In addition, it is almost certain that typed characters will be overwritten by the contents of the attacking packets. 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. Interims 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 Technical Assistance Center (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 | Availability of Fixed Releases* | | | or Platform | | |--------------------------------+---------------------------------------| | 11.1-based Releases | Rebuild | Interim** | Maintenance | |--------------------------------+----------+--------------+-------------| | 11.1CC | ED release for 7000 | 11.1(36) | | | | | series | CC3 | | | |--------------------------------+----------+--------------+-------------| | 12.0-based Releases | Rebuild | Interim** | Maintenance | |--------------------------------+----------+--------------+-------------| | 12.0 | GD release for all | | 12.0(20.4) | | | | platforms | | | | |--------+-----------------------+----------+--------------+-------------| | 12.0S | ED release for all | 12.0(17) | 12.0(18.3)S | 12.0(19)S | | | platforms | ST4 | | | |--------+-----------------------+----------+--------------+-------------| | 12.0ST | ED release for all | | 12.0(18.3)ST | 12.0(19)ST | | | platforms | | | | |--------+-----------------------+---------------------------------------| | 12.0T | ED release for all | To be decided | | | platforms | | |--------+-----------------------+---------------------------------------| | 12.0W5 | ED release for all | | 12.0(20.4)W5 | | | | platforms | | (24.7) | | |--------------------------------+----------+--------------+-------------| | 12.1-based Releases | Rebuild | Interim** | Maintenance | |--------------------------------+----------+--------------+-------------| | 12.1 | LD release for all | | 12.1(9.2) | 12.1(10) | | | platforms | | | | |--------+-----------------------+----------+--------------+-------------| | 12.1E | ED release for all | 12.1 | 12.1(9.5)E | 12.1(8a)E | | | platforms | (8.5)E2 | | | |--------+-----------------------+----------+--------------+-------------| | 12.1EC | ED release for all | 12.1 | 12.1(9.5)EC | | | | platforms | (7.5)EC1 | | | |--------+-----------------------+---------------------------------------| | 12.1T | ED release for all | To be decided | | | platforms | | |--------+-----------------------+---------------------------------------| | 12.1XM | ED release for all | 12.1(5) | | | | | platforms | XM6 | | | |--------------------------------+----------+--------------+-------------| | 12.2-based Releases | Rebuild | Interim** | Maintenance | |--------------------------------+----------+--------------+-------------| | 12.2 | LD release for all | | 12.2(2.5) | 12.2(3) | | | platforms | | | | |--------+-----------------------+----------+--------------+-------------| | 12.2S | LD release for all | | 12.2(3.3)S | | | | platforms | | | | |--------+-----------------------+----------+--------------+-------------| | 12.2T | ED release for all | | 12.2(2.4)T | 12.2(4)T | | | platforms | | | | +------------------------------------------------------------------------+ Obtaining Fixed Software ======================== 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) or by email: tacat_private 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 "psirtat_private" or "security-alertat_private" for software upgrades. Workarounds =========== The workaround is to disable CEF on a router. 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: INTERIM ============================== This is an interim security advisory. Cisco anticipates issuing updated versions of this notice at irregular intervals as there are material changes in the facts, and will continue to update this notice as necessary. The reader is warned that this notice may contain inaccurate or incomplete information. 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 anticipates issuing monthly updates of this notice until it reaches FINAL status. 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/IOS-CEF-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-announceat_private * bugtraqat_private * first-teamsat_private (includes CERT/CC) * ciscoat_private * comp.dcom.sys.cisco * firewallsat_private * 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|2002-February-27 08:00 UTC-0800 |Initial public release| +--------------------------------------------------------------------+ 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 2002 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. -------------------------------------------------------------------------- All contents are Copyright © 1992--2002 Cisco Systems, Inc. All rights reserved. Important Notices and Privacy Statement. -----BEGIN PGP SIGNATURE----- Version: PGP 6.5.3 iQEVAwUBPHz2Qw/VLJ+budTTAQFEdAgAzA1IN81VO4Ci0c7V+P7wfgpdyRNtIEBi XYMRHTFJbOIjY04OtZi1W0EpH4G9X4CAIUxu1FwVhZ3bfHyjNYY43b9+9pt4L/Z/ O7EILxbC9egZQTX7z4ZaShcfSXhV9Ouch5XS+Zs8lI8nSTVpTlWTdyAqnvMoLTNY Rs6Q6yX78gwYaR9G4F2F8qQiNxDYUEntZ+bucWVYfYzydJYqt6IKsTWtPYzTsoQG 3MgcBpbm2oXbNsEDHTX12bNhTIyzLLWu/ruzfxMSXZLGDlqHAG6g8ndk8nW+ksH3 XnZW7Z3V9iKRhdywnhovazQYOH0jjNu4PQDKd7qWnqrgqBufZSqowA== =RSdE -----END PGP SIGNATURE-----
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