Overview

There is a denial-of-service vulnerability in several specific but common configurations of Cisco IOS.

Description

There is a problem involving BGP updates on Cisco routers with BGP4 Prefix Filtering and Inbound Route Maps enabled. A route update with an unrecognized transitive attribute may cause vulnerable routers to crash. This problem does not appear to have been exploited intentionally by attackers, but it has occurred accidentally during normal operation as the result of interaction with another vendor’s product.

More information on this problem is available from Cisco at:

<http://www.cisco.com/warp/public/707/ios-bgp-attr-corruption-pub.shtml&gt;

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Impact

Attackers that are able to send malformed BGP updates can cause vulnerable routers to crash causing network outages. Under certain circumstances, an attacker may be able to use the BGP infrastructure to propogate the bad route update to multiple routers.

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Solution

Cisco has released an advisory that provides a list of affected products, along with instructions for obtaining fixed software. Because there are many possible combinations of hardware and software configurations, the CERT/CC recommends that all users of IOS and software consult the following Cisco Security Advisory:

|

<http://www.cisco.com/warp/public/707/ios-bgp-attr-corruption-pub.shtml&gt;

Vendor Information

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Cisco Systems Inc. __ Affected

Updated: May 10, 2001

Status

Affected

Vendor Statement

For more information, see the Cisco advisory.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

-----BEGIN PGP SIGNED MESSAGE-----

`Cisco Security Advisory: Cisco IOS BGP Attribute Corruption Vulnerability

Revision 1.0`

For Public Release 2001 May 10 08:00 AM US/Pacific (UTC -0700)

------------------------------------------------------------------------

Summary =======

A Border Gateway Protocol (BGP) UPDATE contains Network Layer Reachability Information (NLRI) and attributes that describe the path to the destination. An unrecognized transitive attribute can cause failures in Cisco IOS routers, ranging from a crash upon receipt of the unrecognized transitive attribute, to a later failure upon attempt to clear the unrecognized transitive attribute. Specific but common configurations are affected, and described below. The failure was discovered because of a malfunction in the BGP implementation of another vendor. There is no workaround. Affected customers are urged to upgrade to fixed code.

This vulnerability has been assigned Cisco bug ID CSCdt79947.

The complete text of this advisory will be located at <http://www.cisco.com/warp/public/707/ios-bgp-attr-corruption-pub.shtml>

Affected Products =================

Configurations including BGP4 Prefix Filtering with Inbound Route Maps are vulnerable. BGP with prefix or inbound routemap filtering was introduced in Cisco IOS® Software version 11.2 The following versions of Cisco IOS Software are affected and listed in the table below: 11.CC and its derivatives, 11.2 and its derivaties, 11.3, 11.3T, 12.0, 12.0S and special branches taken out of 12.0 are all affected. The versions of Cisco IOS Software based on 12.1, 12.0(5)T, 12.2, 12.0ST, and 12.1(E) are not affected. The following products are affected if they run a Cisco IOS software release that has the defect. To determine if a Cisco product is running an affected IOS, log in to the device and issue the show version command. Cisco IOS software will identify itself as "Internetwork Operating System Software" or "IOS (tm)" software and will display a version number. Other Cisco devices either will not have the show version command, or will give different output. Compare the version number obtained from the router with the versions presented in the Software Versions and Fixes section
below.

Cisco devices that may be running with affected Cisco IOS software releases include:

* Cisco routers in the AGS/MGS/CGS/AGS+, IGS, RSM, 800, ubr900, 1000, 1400, 1500, 1600, 1700, 2500, 2600, 3000, 3600, 3800, 4000, 4500, 4700, AS5200, AS5300, AS5800, 6400, 7000, 7200, ubr7200, 7500, and 12000 series.

Cisco devices that may be running Cisco IOS Software, but do NOT support BGP and are therefore not vulnerable include:

` * Most recent versions of the LS1010 ATM switch.

• The Catalyst 2900XL LAN switch only if it is running IOS.
• The Catalyst 1900, 2800, 2900, 3000, and 5000 series LAN switches.
• The Cisco DistributedDirector.`

If you are not running Cisco IOS software, you are not affected by this vulnerability. If you are not running BGP, you are not affected by this vulnerability.

Cisco products that do not run Cisco IOS software and are not affected by this defect include, but are not limited to:

` * 700 series dialup routers (750, 760, and 770 series) are not affected.

• The Catalyst 6000 is not affected if it is not running IOS.
• WAN switching products in the IGX and BPX lines are not affected.
• The MGX (formerly known as the AXIS shelf) is not affected.
• No host-based software is affected.
• The Cisco PIX Firewall is not affected.
• The Cisco LocalDirector is not affected.
• The Cisco Cache Engine is not affected.`

Details =======

A Border Gateway Protocol (BGP) UPDATE contains Network Layer Reachability Information (NLRI) and attributes that describe the path to the destination. Each path attribute is a type, length, value (TLV) object. This failure occurs as a result of memory corruption and only in configurations using specific inbound route filtering. The failure was discovered because of a malfunction in the BGP implementation of another vendor. There is no workaround.

Impact ======

The vulnerability can be exercised repeatedly, affecting core routers, creating widespread network outages. This vulnerability can only be exercised in configurations that include both BGP and inbound route filtering on affected software.

Software Versions and Fixes ===========================

The following table summarizes the Cisco IOS software releases that are known to be affected, and the earliest estimated dates of availability for the recommended fixed versions. Dates are always tentative and subject to change.

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 receive 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 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 later in this notice.

More information on Cisco IOS Software release names and abbreviations is available at <http://www.cisco.com/warp/public/cc/pd/iosw/iore/prodlit/537_pp.htm>.

+===========================================================================+ Train Description of Availability of Fixed Releases* Image or Platform +===========================================================================+ 11.0-based Releases Rebuild Interim Maintenance +===========================================================================+ 11.0 Major GD release Not vulnerable for all platforms +===========================================================================+ 11.1-based Releases Rebuild Interim Maintenance +===========================================================================+ 11.1 Major release for Not vulnerable all platforms +----------+------------------+-----------------+------------+--------------+ ED release for 11.1AA access servers: Not vulnerable 1600, 3200, and 5200 series. +----------+------------------+-----------------+------------+--------------+
Platform-specific End of Engineering 11.1CA support for 7500, 7200, 7000, and RSP Not scheduled +----------+------------------+-----------------+------------+--------------+ ISP train: added support for FIB, 11.1(36)CC2 11.1CC CEF, and NetFlow on 7500, 7200, Not scheduled 7000, and RSP +----------+------------------+-----------------+------------+--------------+ Added support for End of Engineering 11.1CT Tag Switching on 7500, 7200, 7000, and RSP Upgrade recommended to 12.0(14)ST +----------+------------------+-----------------+------------+--------------+ 11.1IA Distributed Not Vulnerable Director only +===========================================================================+ 11.2-based Releases Rebuild Interim Maintenance +===========================================================================+
Major release, End of Engineering 11.2 general deployment Not scheduled +----------+------------------+-----------------+------------+--------------+ Platform-specific support for IBM End of Engineering 11.2BC networking, CIP, and TN3270 on 7500, 7000, and Upgrade recommended to 12.1(8) RSP +----------+------------------+-----------------+------------+--------------+ End of Engineering 11.2F Feature train for all platforms Upgrade recommended +----------+------------------+-----------------+------------+--------------+ Early deployment End of Engineering 11.2GS release to support 12000 GSR Upgrade recommended to 12.0(17)S +----------+------------------+-----------------+------------+--------------+ End of Engineering 11.2P New platform support Upgrade recommended to 12.0(17)
+----------+------------------+-----------------+------------+--------------+ 11.2SA Catalyst 2900XL Not vulnerable switch only +----------+------------------+-----------------+------------+--------------+ 11.2WA3 LightStream 1010 Not vulnerable ATM switch +----------+------------------+-----------------+------------+--------------+ Initial release End of Engineering 11.2(4)XAf for the 1600 and 3600 Upgrade recommended +----------+------------------+-----------------+------------+--------------+ Initial release for the 5300 and End of Engineering 11.2(9)XA digital modem support for the Upgrade recommended 3600 +===========================================================================+ 11.3-based Releases Rebuild Interim Maintenance +===========================================================================+ End of Engineering
11.3 Major release for all platforms Upgrade recommended to 12.0(17) +----------+------------------+-----------------+------------+--------------+ ED for dial platforms and End of Engineering 11.3AA access servers: 5800, 5200, 5300, Upgrade recommended to 12.0(17) 7200 +----------+------------------+-----------------+------------+--------------+ Early deployment End of Engineering 11.3DA train for ISP DSLAM 6200 platform Upgrade recommended to 12.1(5)DA1 +----------+------------------+-----------------+------------+--------------+ Early deployment train for End of Engineering ISP/Telco/PTT 11.3DB xDSL broadband concentrator platform, (NRP) Upgrade recommended to 12.1(4)DB1 for 6400 +----------+------------------+-----------------+------------+--------------+ Short-lived ED End of Engineering
11.3HA release for ISR 3300 (SONET/SDH router) Upgrade recommended to 12.0 +----------+------------------+-----------------+------------+--------------+ MC3810 Not available 11.3MA functionality only Not scheduled +----------+------------------+-----------------+------------+--------------+ Voice over IP, End of Engineering 11.3NA media convergence, various platforms Upgrade recommended to 12.0(5)T +----------+------------------+-----------------+------------+--------------+ Early deployment End of Engineering 11.3T major release, feature-rich for early adopters Upgrade recommended to 12.0(17) +----------+------------------+-----------------+------------+--------------+ Multilayer Switching and Multiprotocol End of Engineering over ATM 11.3WA4 functionality for
Catalyst 5000 RSM, 4500, 4700, Upgrade recommended 7200, 7500, LightStream 1010 +----------+------------------+-----------------+------------+--------------+ End of Engineering 11.3(2)XA Introduction of ubr7246 and 2600 Upgrade recommended +===========================================================================+ 12.0-based Releases Rebuild Interim Maintenance +===========================================================================+ General 12.0 deployment 12.0(17) release for all 2001-Apr-23 platforms +----------+------------------+-----------------+------------+--------------+ Unavailable 12.0DA xDSL support: 6100, 6200 Upgrade recommended to 12.1(5)DA1 +----------+------------------+-----------------+------------+--------------+
Early Deployment (ED) release, which delivers Unavailable support for the 12.0DB Cisco 6400 Universal Access Concentrator (UAC) for Node Upgrade recommended to 12.1(4)DB1 Switch Processor (NSP) +----------+------------------+-----------------+------------+--------------+ Early Deployment (ED) release, which delivers Unavailable support for the 12.0DC Cisco 6400 Universal Access Concentrator (UAC) for Node Upgrade recommended to 12.1(5)DC Route Processor (NRP) +----------+------------------+-----------------+------------+--------------+ 12.0(15)S3, 12.0(17)S 12.0(16)S1 12.0(16.06)S 2001-May-07 12.0S Core/ISP support: GSR, RSP, c7200 2001-April-23 2001-April-30
+----------+------------------+-----------------+------------+--------------+ 12.0SC Cable/broadband Not vulnerable ISP: ubr7200 +----------+------------------+-----------------+------------+--------------+ 12.0SL 10000 ESR: c10k Not vulnerable +----------+------------------+-----------------+------------+--------------+ Cisco IOS software Release12.0ST is an early deployment (ED) 12.0ST release for the Not vulnerable Cisco 7200, 7500/7000RSP and 12000 (GSR) series routers for Service Providers (ISPs). +----------+------------------+-----------------+------------+--------------+ Early Deployment(ED): 12.0T VPN, Distributed 12.0(5)T Director, various platforms +----------+------------------+-----------------+------------+--------------+ Catalyst
switches: 12.0(10)W5(18g) cat2948g-l3, 2001-Apr-20 cat4232 12.0W5 +------------------+-----------------+------------+--------------+ cat8510c, cat8540c, c6msm, 12.0(16)W5(21) ls1010, cat8510m, cat8540m, c5atm 2001-May-21 +----------+------------------+-----------------+------------+--------------+ Catalyst 12.0WT switches: Not vulnerable cat4840g +----------+------------------+-----------------+------------+--------------+ Early Deployment Unavailable 12.0XA (ED): limited Upgrade recommended to 12.1(8), available platforms 2001-Apr-23 +----------+------------------+-----------------+------------+--------------+ Short-lived early Unavailable 12.0XB deployment Upgrade recommended to 12.1(8), available release 2001-Apr-23
+----------+------------------+-----------------+------------+--------------+ Early Deployment Unavailable 12.0XC (ED): limited Upgrade recommended to 12.1(8), available platforms 2001-Apr-23 +----------+------------------+-----------------+------------+--------------+ Early Deployment Unavailable 12.0XD (ED): limited Upgrade recommended to 12.1(8), available platforms 2001-Apr-23 +----------+------------------+-----------------+------------+--------------+ Early Deployment 12.0XE (ED): limited Not Vulnerable platforms +----------+------------------+-----------------+------------+--------------+ Early Deployment Unavailable 12.0XF (ED): limited Upgrade recommended to 12.1(8), available platforms 2001-Apr-23 +----------+------------------+-----------------+------------+--------------+ Early Deployment Unavailable 12.0XG (ED): limited Upgrade recommended to 12.1(8), available
platforms 2001-Apr-23 +----------+------------------+-----------------+------------+--------------+ Early Deployment Unavailable 12.0XH (ED): limited Upgrade recommended to 12.1(8), available platforms 2001-Apr-23 +----------+------------------+-----------------+------------+--------------+ Early Deployment Unavailable 12.0XI (ED): limited Upgrade recommended to 12.1(8), available platforms 2001-Apr-23 +----------+------------------+-----------------+------------+--------------+ Early Deployment Unavailable 12.0XJ (ED): limited Upgrade recommended to 12.1(8), available platforms 2001-Apr-23 +----------+------------------+-----------------+------------+--------------+ Early Deployment 12.0XK (ED): limited Not vulnerable platforms +----------+------------------+-----------------+------------+--------------+ Early Deployment
12.0XL (ED): limited Not vulnerable platforms +----------+------------------+-----------------+------------+--------------+ Short-lived early 12.0XM deployment Not vulnerable release +----------+------------------+-----------------+------------+--------------+ Early Deployment 12.0XN (ED): limited Not vulnerable platforms +----------+------------------+-----------------+------------+--------------+ Early Deployment 12.0XP (ED): limited Not vulnerable platforms +----------+------------------+-----------------+------------+--------------+ Short-lived early 12.0XQ deployment Not vulnerable release +----------+------------------+-----------------+------------+--------------+ Short-lived early 12.0XR deployment Not vulnerable release +----------+------------------+-----------------+------------+--------------+
Short-lived early 12.0XS deployment Not vulnerable release +----------+------------------+-----------------+------------+--------------+ Early Deployment 12.0XU (ED): limited Not vulnerable platforms +----------+------------------+-----------------+------------+--------------+ Short-lived early 12.0XV deployment Not vulnerable release +===========================================================================+ 12.1-based and Later Releases Rebuild Interim Maintenance +===========================================================================+ General 12.1 deployment Not vulnerable release for all platforms +===========================================================================+ Notes +===========================================================================+
* All dates are estimated and subject to change.

** Interim releases are subjected to less rigorous testing than regular maintenance releases, and may have serious bugs. +===========================================================================+

Getting Fixed Software

Cisco is offering free software upgrades to remedy 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 via the Software Center on Cisco's Worldwide Web site at <http://www.cisco.com>.

Customers without contracts 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: [email protected]`

See <http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml> for additional TAC contact information, including instructions and e-mail addresses for use in various languages.

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 "[email protected]" or "[email protected]" for software upgrades.

Workarounds ===========

There are no known workarounds for this vulnerablity. Please upgrade to fixed versions.

Exploitation and Public Announcements =====================================

Cisco has had no reports of malicious exploitation of this vulnerability. The failure was discovered because of a malfunction in the BGP implementation of another vendor, which caused a series of crashes that led to the identification of this issue.

Cisco knows of no public announcements of this vulnerability before the date of this notice.

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.

Distribution ============

This notice will be posted on Cisco's Worldwide Web site at <http://www.cisco.com/warp/public/707/ios-bgp-attr-corruption-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:

` * [email protected]

• [email protected]
• [email protected]
• [email protected] (includes CERT/CC)
• [email protected]
• [email protected]
• comp.dcom.sys.cisco
• 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 Number1.0 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.

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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.

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If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%23106392 Feedback>).

CVSS Metrics

Group	Score	Vector
Base
Temporal
Environmental

References

• <http://www.cisco.com/warp/public/707/ios-bgp-attr-corruption-pub.shtml&gt;
• <http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_c/ipcprt2/1cdbgp.htm#xtocid124918&gt;
• <http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_c/ipcprt2/1cdbgp.htm#xtocid124934&gt;
• <http://www.securityfocus.com/bid/2733&gt;

Acknowledgements

The CERT/CC would like to thank Cisco Systems for providing a description of this vulnerability and a patch to address it.

This document was written by Ian A. Finlay and is based on information obtained from a Cisco Security Advisory.

Other Information

CVE IDs:	CVE-2001-0650
Severity Metric:	21.55 Date Public: