Cisco Security Advisory-
A Cisco device running IOS and enabled for the Border Gateway Protocol (BGP) is vulnerable to a Denial of Service (DOS) attack from a malformed BGP packet. The BGP protocol is not enabled by default, and must be configured in order to accept traffic from an explicitly defined peer. Unless the malicious traffic appears to be sourced from a configured, trusted peer, it would be difficult to inject a malformed packet.
Cisco has made free software available to address this problem.
This advisory is available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20040616-bgp.
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This section provides details on affected products.
Vulnerable Products
This issue affects all Cisco devices running any unfixed version of Cisco IOS or Cisco IOS XR code and configured for BGP routing.
A router which is running the BGP process will have a line in the config defining the AS number, which can be seen by issuing the command show running-config:
router bgp <AS number>
This vulnerability is present in any unfixed version of IOS, from the beginning of support for the BGP protocol, including versions 9.x, 10.x, 11.x and 12.x.
This vulnerability is present in any unfixed version of IOS XR, from the beginning of support for the BGP protocol, including versions 2.0.X and 3.0.X
To determine the software running on a Cisco product, log in to the device and issue the show version command to display the system banner. Cisco IOS software will identify itself as "Internetwork Operating System Software" or simply "IOS®." On the next line of output, the image name will be displayed between parentheses, followed by "Version" and the IOS release name. Other Cisco devices will not have the show version command or will give different output.
The following example identifies a Cisco product running IOS release 12.0(3) with an installed image name of C2500-IS-L:
Cisco Internetwork Operating System Software IOS (TM) 2500 Software (C2500-IS-L), Version 12.0(3), RELEASE SOFTWARE
The release train label is "12.0."
The next example shows a product running IOS release 12.0(2a)T1 with an image name of C2600-JS-MZ:
Cisco Internetwork Operating System Software IOS (tm) C2600 Software (C2600-JS-MZ), Version 12.0(2a)T1, RELEASE SOFTWARE (fc1)
Additional information about Cisco IOS release naming can be found at http://www.cisco.com/warp/public/620/1.html.
Products Confirmed Not Vulnerable
Products confirmed not to be vulnerable include devices which cannot participate in BGP or cannot be configured for BGP.
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The Border Gateway Protocol (BGP) is a routing protocol defined by RFC 1771, and designed to manage IP routing in large networks. An affected Cisco device running a vulnerable version of Cisco IOS software and enabling the BGP protocol will reload when a malformed BGP packet is received. BGP runs over TCP, a reliable transport protocol which requires a valid three way handshake before any further messages will be accepted. The Cisco IOS implementation of BGP requires the explicit definition of a neighbor before a connection can be established, and traffic must appear to come from that neighbor. These implementation details make it very difficult to send a BGP packet to a Cisco IOS device from an unauthorized source.
A Cisco device receiving an invalid BGP packet will reset and may take several minutes to become fully functional. This vulnerability may be exploited repeatedly resulting in an extended DOS attack. This issue is documented in bug IDs CSCdu53656 ( registered customers only) and CSCea28131 ( registered customers only) .
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The effectiveness of any workaround is dependent on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround is the most appropriate for use in the intended network before it is deployed.
For additional information regarding BGP security risk assessment, mitigation techniques, and deployment best practices, please consult ftp://ftp-eng.cisco.com/cons/isp/security/BGP-Risk-Assesment-v.pdf.
BGP MD5
Under normal circumstances, due to inherent security factors in the TCP protocol such as sequence number checks, it is difficult but possible to forge an appropriate packet to exploit this problem. Configuring your Cisco IOS device for BGP MD5 authentication is a valid workaround to protect the vulnerable device.
This can be configured as shown in the following example:
router(config)# router bgp router(config-router)# neighbor <IP_address> password <enter_your_secret_here>
It is necessary to configure the same shared MD5 secret on both peers and at the same time. Failure to do so will break the existing BGP session and the new session will not get established until the exact same secret is configured on both devices. For a detailed discussion on how to configure BGP, refer to the following document:
Once the secret is configured, it is prudent to change it periodically. The exact period must fit within your company security policy but it should not be longer than a few months. When changing the secret, again it must be done at the same time on both devices. Failure to do so will break your existing BGP session. The exception is if your Cisco IOS software release contains the integrated CSCdx23494 ( registered customers only) fix on both sides of the connection. With this fix, the BGP session will not be terminated when the MD5 secret is changed only on one side. The BGP updates, however, will not be processed until either the same secret is configured on both devices or the secret is removed from both devices.
Infrastructure Access Control Lists
Although it is often difficult to block traffic transiting your network, it is possible to identify traffic which should never be allowed to target your infrastructure devices and block that traffic at the border of your network. Infrastructure ACLs are considered a network security best practice and should be considered as a long-term addition to good network security as well as a workaround for this specific vulnerability. The white paper entitled "Protecting Your Core: Infrastructure Protection Access Control Lists" presents guidelines and recommended deployment techniques for infrastructure protection ACLs:
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Note: Many of the releases in this table were fixed prior to the release of other IOS advisories. Read the table carefully to determine if your IOS release contains these fixes. Most fixed releases for the TCP and SNMP advisories such as https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20040420-snmp and https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20040420-tcp-ios contained the fixes for this BGP advisory.
Each row of the Cisco IOS software table (below) 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 (the "First Fixed Release") and the anticipated date of availability for each are listed in the "Rebuild," "Interim," and "Maintenance" columns. A device running a release in the given train that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. The release should be upgraded at least to the indicated release or a later version (greater than or equal to the First Fixed Release label). When selecting a release, keep in mind the following definitions:
Maintenance
Most heavily tested, stable, and highly recommended release of a release train in any 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 repair the vulnerability.
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. Interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available through manufacturing, and usually they are not available for customer download from Cisco.com without prior arrangement with the Cisco TAC.
In all cases, customers should exercise caution to confirm that the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new software release. If the information is not clear, contact the Cisco TAC for assistance as shown in the Obtaining Fixed Software section below.
More information on Cisco IOS software release names and abbreviations is available at http://www.cisco.com/warp/public/620/1.html.
The fixes will be available at the Software Center located at http://www.cisco.com/tacpage/sw-center/.
For software installation and upgrade procedures, see http://www.cisco.com/warp/public/130/upgrade_index.shtml.
For a current view of all posted and repaired images for Cisco IOS, please check the listing available to registered Cisco.com users at: http://www.cisco.com/tacpage/sw-center/sw-ios.shtml.
Major Release
Availability of Repaired Releases*
Affected 11.1-Based Release
Rebuild
Interim**
Maintenance
11.1
Migrate to 11.2 or later
11.1AA
Migrate to 11.2P or later
11.1CA
Migrate to 12.0 or later
11.1CC
Migrate to 12.0 or later
Affected 11.2-Based Release
Rebuild
Interim**
Maintenance
11.2
11.2(26g)
11.2P
11.2(26)P7
11.2SA
Not Vulnerable
Affected 11.3-Based Release
Rebuild
Interim**
Maintenance
11.3
11.3(11f)
11.3T
11.3(11b)T5
Affected 12.0-Based Release
Rebuild
Interim**
Maintenance
12.0
12.0(27)
12.0DA
Migrate to 12.2DA or later
12.0S
12.0(21)S7
12.0(22)S2e
12.0(22)S3c
12.0(22)S4a
12.0(22)S5
12.0(23)S3
12.0(24)S2
12.0(25)S1
12.0(26)S
12.0SL
Migrate to 12.0(23)S3 or later
12.0ST
12.0(17)ST10 Available upon request
12.0(21)ST7
Migrate to 12.0(26)S2 or later
12.0SV
12.0(27)SV
12.0SX
12.0(25)SX
12.0SZ
12.0(23)SZ3
12.0(26)SZ
Migrate to 12.0(26)S2 or later
12.0T
Migrate to 12.1 or later
12.0W5
12.0(16)W5(21c)
12.0(25)W5(27b)
12.0(26)W5(28a)
12.0(27)W5(29)
12.0WC
Not Vulnerable
12.0WX
Migrate to 12.0W5 or later
12.0XA
Migrate to 12.1 latest or later
12.0XC
Migrate to 12.1 latest or later
12.0XD
Migrate to 12.1 latest or later
12.0XE
Migrate to 12.1E latest or later
12.0XG
Migrate to 12.1 latest or later
12.0XH
Migrate to 12.1 latest or later
12.0XI
Migrate to 12.1 latest or later
12.0XJ
Migrate to 12.1 latest or later
12.0XK
Migrate to 12.1T latest or later
12.0XL
Migrate to 12.2 latest or later
12.0XN
Migrate to 12.1 latest or later
12.0XP
Not Vulnerable
12.0XR
Migrate to 12.2 latest or later
12.0XS
Migrate to 12.1E latest or later
12.0XU
Not Vulnerable
Affected 12.1-Based Release
Rebuild
Interim**
Maintenance
12.1
12.1(20)
12.1AA
Migrate to 12.2 latest or later
12.1AX
Not Vulnerable
12.1AY
Not Vulnerable
12.1AZ
12.1(14)AZ
12.1DA
Migrate to 12.2DA or later
12.1DB
Migrate to 12.2B or later
12.1E
12.1(6)E12.0
12.1(8b)E14
12.1(11b)E12.0
12.1(12c)E7
12.1(13)E6
12.1(14)E4
12.1(19)E
12.1(20)E
12.1EA
12.1(14)EA1
12.1EB
12.1(14)EB1
12.1EC
12.1(19)EC
12.1EO
12.1(19)EO
12.1EV
12.1(12c)EV2
12.1EW
12.1(19)EW
12.1EX
Migrate to 12.1(14)E4 or later
12.1EY
Migrate to 12.1(14)E4 or later
12.1T
12.1(5)T19
12.1XA
Migrate to 12.1(5)T19 or later
12.1XB
Migrate to 12.1(5)T19 or later
12.1XC
Migrate to 12.1(5)T19 or later
12.1XD
Migrate to 12.2 or later
12.1XE
Migrate to 12.1E latest or later
12.1XF
Migrate to 12.2(4)T6 or later
12.1XG
Migrate to 12.2(4)T6 or later
12.1XH
Migrate to 12.2 or later
12.1XI
Migrate to 12.2 latest or later
12.1XJ
Migrate to 12.2(4)T6 or later
12.1XL
Migrate to 12.2T latest or later
12.1XM
Migrate to 12.2T latest or later
12.1XP
Migrate to 12.2(4)T6 or later
12.1XQ
Migrate to 12.2T latest or later
12.1XR
Migrate to 12.2T latest or later
12.1XT
Migrate to 12.2(4)T6 or later
12.1XU
Migrate to 12.2T latest or later
12.1XV
Migrate to 12.2XB or later
12.1XY
Migrate to 12.2XB or later
12.1YA
Migrate to 12.2(8)T10 or later
12.1YB
Migrate to 12.2(4)T6 or later
12.1YC
Migrate to 12.2(8)T10 or later
12.1YD
Migrate to 12.2(8)T10 or later
12.1YH
Migrate to 12.2(13)T5 or later
12.1YJ
Not Vulnerable
Affected 12.2-Based Release
Rebuild
Interim**
Maintenance
12.2
12.2(10d)
12.2(12e)
12.2(12h)M1
12.2(13c)
12.2(16a)
12.2(17)
12.2B
12.2(15)B1
12.2BC
12.2(15)BC1
12.2BW
Migrate to 12.2(15)T12 or later
12.2BX
12.2(16)BX
12.2BY
Migrate to 12.2(15)B1 or later
12.2BZ
Migrate to 12.2(16)BX or later
12.2CX
12.2(15)CX
12.2DA
12.2(12)DA6
12.2DD
Migrate to 12.2(15)B1 or later
12.2DX
Migrate to 12.2(15)B1 or later
12.2EW
12.2(18)EW
12.2JA
12.2(13)JA
12.2S
12.2(14)S2
12.2(18)S
12.2SE
12.2(18)SE
12.2SU
12.2(14)SU
12.2SV
12.2(18)SV
12.2SW
12.2(18)SW
12.2SX
12.2(14)SX2
12.2SXA
12.2(17b)SXA
12.2SXB
12.2(17d)SXB
12.2SY
12.2(14)SY
12.2SZ
12.2(14)SZ2
12.2T
12.2(4)T6
12.2(8)T10
12.2(11)T9
12.2(13)T5
12.2(15)T4
12.2XA
Migrate to 12.2(11)T9 or later
12.2XB
12.2(2)XB16
12.2XD
Migrate to 12.2(8)T10 or later
12.2XE
Migrate to 12.2(8)T10 or later
12.2XG
Migrate to 12.2(8)T10 or later
12.2XH
Migrate to 12.2(11)T9 or later
12.2XI
Migrate to 12.2(11)T9 or later
12.2XJ
Migrate to 12.2(11)T9 or later
12.2XK
Migrate to 12.2(11)T9 or later
12.2XL
Migrate to 12.2(15)T4 or later
12.2XM
Migrate to 12.2(15)T4 or later
12.2XN
Migrate to 12.2(11)T9 or later
12.2XQ
Migrate to 12.2(11)T9 or later
12.2XS
Migrate to 12.2(11)T9 or later
12.2XT
Migrate to 12.2(11)T9 or later
12.2XU
Migrate to 12.2(15)T12 or later
12.2XW
Migrate to 12.2(11)T9 or later
12.2YA
Migrate to 12.2(15)T4 or later
12.2YB
Migrate to 12.2(15)T4 or later
12.2YC
Migrate to 12.2(11)T11 or later
12.2YD
Migrate to 12.2(8)YY or later
12.2YE
Migrate to 12.2S or later
12.2YF
Migrate to 12.2(15)T4 or later
12.2YG
Migrate to 12.2(13)T5 or later
12.2YH
Migrate to 12.2(15)T4 or later
12.2YJ
Migrate to 12.2(15)T4 or later
12.2YL
Migrate to 12.3(2)T or later
12.2YM
Migrate to 12.3(2)T or later
12.2YN
Migrate to 12.3(2)T or later
12.2YO
Migrate to 12.2(14)SY or later
12.2YP
12.2(11)YP1
12.2YQ
Migrate to 12.3(4)T or later
12.2YR
Migrate to 12.3(4)T or later
12.2YS
Migrate to 12.3T or later
12.2YT
Migrate to 12.2(15)T4 or later
12.2YU
Migrate to 12.3(4)T or later
12.2YV
Migrate to 12.3(4)T or later
12.2YW
Migrate to 12.3(2)T or later
12.2YX
Migrate to 12.2(14)SU or later
12.2YY
12.2(8)YY3
12.2YZ
Migrate to 12.2(14)SZ or later
12.2ZA
12.2(14)ZA2
12.2ZB
Migrate to 12.3T or later
12.2ZC
Migrate to 12.3T or later
12.2ZE
Migrate to 12.3 or later
12.2ZF
Migrate to 12.3(4)T or later
12.2ZG
Migrate to 12.3(4)T or later
12.2ZH
Migrate to 12.3(4)T or later
12.2ZI
Migrate to 12.2(18)S or later
12.2ZK
12.2(15)ZK
12.2ZL
12.2(15)ZL
12.2ZN
Migrate to 12.3(2)T or later
12.2ZO
12.2(15)ZO
12.2ZP
12.2(13)ZP
Affected 12.3-Based Release
Rebuild
Interim**
Maintenance
12.3
Not Vulnerable
12.3T
Not Vulnerable
Product
First Fixed Release
Cisco IOS XR
IOS XR 3.2.5
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The research which led to this vulnerability being discovered was announced in a public announcement at NANOG in June 2003. The Cisco PSIRT team is not aware of any malicious use of the vulnerabilities described in this advisory. We were made aware of this issue through internal testing as well as notification from a research team at the University of California at Santa Barbara.
The Cisco PSIRT is not aware of any malicious use of the vulnerability described in this advisory.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Revision 1.1
12-January-2006
Updated the Vulnerable Products section. Added the Products/First Fixed Release table to the Software Versions and Fixes section.
Revision 1.0
16-June-2004
Initial Public Release
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