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Cisco Routers running Internetwork Operating System (IOS) that supports Multi Protocol Label Switching (MPLS) are vulnerable to a Denial of Service (DoS) attack on interfaces where MPLS is not configured. A system that supports MPLS is vulnerable even if that system is not configured for MPLS.
The vulnerability is only present in Cisco IOS release trains based on 12.1T, 12.2, 12.2T, 12.3 and 12.3T. Releases based on 12.1 mainline, 12.1E and all releases prior to 12.1 are not vulnerable.
Cisco has made free software available to address this vulnerability.
There are workarounds available to mitigate the effects.
This issue is tracked by CERT/CC VU#583638.
This advisory is available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050126-les.
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This section provides details on affected products.
Vulnerable Products
Only the following products running a vulnerable version of IOS that support MPLS are affected.
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2600 and 2800 series routers
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3600, 3700 and 3800 series routers
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4500 and 4700 series routers
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5300, 5350 and 5400 series Access Servers
Products that are not listed above are not affected.
MPLS is not supported in IP and IP Plus feature sets. Therefore, products running an IOS version with an IP or IP Plus feature set are not vulnerable.
An attack can only be launched at systems that are not configured for MPLS Traffic Engineering and on the interfaces where MPLS is not enabled. MPLS enabled interfaces can be determined by the show mpls interfaces command.
An unaffacted system where MPLS is not supported will give an output similar to the following.
Router#show mpls interfaces ^ % Invalid input detected at '^' marker. Router#
MPLS can be enabled in different ways on a router. In the below output, a router is shown that has MPLS enabled for IP on interface Ethernet0/0.
Router#show mpls interfaces Interface IP Tunnel Operational Ethernet0/0 Yes (tdp) No Yes Router#
When MPLS for IP is enabled on an interface, the router is immune to the attacks coming from that interface but vulnerable to the attacks coming from other interfaces. Enabling MPLS for IP on all interfaces of the router will make the router immune to attacks coming from any interface. An interface that has MPLS for IP enabled will have mpls ip or tag-switching ip command in the interface configuration.
MPLS Traffic Engineering (TE) provides a better protection against this vulnerability. If MPLS TE is enabled globally, the router will be immune to the attacks coming from any interface. A router that has MPLS TE enabled will have mpls traffic-eng tunnels command in the show running-config output.
Products Confirmed Not Vulnerable
These products are not vulnerable:
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Products that are not running Cisco IOS are not vulnerable.
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Products running Cisco IOS versions 12.0 and earlier and 12.1 mainline are not vulnerable.
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Products that are not mentioned in the Affected Products section are not vulnerable (including but not limited to Cisco 7200, 7500, 12000 series and Catalyst systems).
No other Cisco products are currently known to be affected by these vulnerabilities.
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2600 and 2800 series routers
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Multi Protocol Label Switching (MPLS) is a vendor-independent protocol that integrates layer-2 (as defined in the Open System Interconnection Reference Model) information into layer-3. More information on MPLS can be found at http://www.cisco.com/warp/public/732/Tech/mpls.
A vulnerability exists in the processing of an MPLS packet that is received on an interface where MPLS is disabled. A router that is configured for MPLS Traffic Engineering is immune to attacks coming from any interface.
A Cisco device receiving a crafted packet on an MPLS disabled interface 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 bugs ID CSCeb56909 ( registered customers only) and CSCec86420 ( registered customers only) .
Such crafted packets can only be sent from the local network segment.
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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.
Warning: Using this workaround may affect the operation of your network and might cause problems. Therefore it is strongly recommended that you do a code upgrade if you are affected. It is not recommended that you use the workaround as a long term solution.
Enabling MPLS Traffic Engineering (MPLS TE) globally can be used as a workaround to mitigate this vulnerability. Since MPLS requires Cisco Express Forwarding (CEF) in order to work, CEF needs to be enabled first in order to enable MPLS TE.
CEF and MPLS TE can be enabled by the following commands.
Router(config)# ip cef Router(config)# mpls traffic-eng tunnels
Having MPLS TE enabled will make the router immune to the attacks coming from any interface.
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When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.
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 Technical Assistance Center ("TAC") or your contracted maintenance provider for assistance.
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" 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).
For more information on the terms "Rebuild" and "Maintenance," consult the following URL:
http://www.cisco.com/warp/public/620/1.html
Major Release
Availability of Repaired Releases
Affected 12.1-Based Release
Rebuild
Maintenance
12.1DB
Migrate to 12.3(4)T or later
12.1DC
Migrate to 12.3(4)T or later
12.1T
Migrate to 12.2 or later
12.1XG
Migrate to 12.3 or later
12.1XI
Migrate to 12.2 or later
12.1XJ
Migrate to 12.3 or later
12.1XL
Migrate to 12.3 or later
12.1XM
Migrate to 12.3 or later
12.1XP
Migrate to 12.3 or later
12.1XQ
Migrate to 12.3 or later
12.1XR
Migrate to 12.3 or later
12.1XT
Migrate to 12.3 or later
12.1XU
Migrate to 12.3 or later
12.1XV
Migrate to 12.3 or later
12.1YA
Migrate to 12.3 or later
12.1YB
Migrate to 12.3 or later
12.1YC
Migrate to 12.3 or later
12.1YD
Migrate to 12.3 or later
12.1YE
Migrate to 12.3 or later
12.1YF
Migrate to 12.3 or later
12.1YH
Migrate to 12.3 or later
12.1YI
Migrate to 12.3 or later
Affected 12.2-Based Release
Rebuild
Maintenance
12.2
12.2(10g)
12.2(13e)
12.2(16f)
12.2(17d)
12.2(19b)
12.2(21a)
12.2(23)
12.2B
12.2(2)B through 12.2(4)B7, Migrate to 12.3 or later
12.2(4)B8 and forward, Migrate to 12.3(4)T or later
12.2BC
12.2(15)BC2
12.2BW
Migrate to 12.3 or later
12.2BX
Migrate to 12.3(7)XI1 or later
12.BY
Migrate to 12.3(4)T or later
12.2BZ
Migrate to 12.3(7)XI1 or later
12.2CX
Migrate to 12.2(15)BC2
12.2CY
Migrate to 12.2(15)BC2
12.2CZ
12.2(15)CZ
12.2DA
12.2(12)DA6
12.2DD
Migrate to 12.3(4)T or later
12.2DX
Migrate to 12.3(4)T or later
12.2EW
12.2(18)EW
12.2EWA
12.2(20)EWA
12.2JA
12.2(15)JA
12.2JK
12.2(15)JK
12.2MB
Migrate to 12.2(19)SW
12.2MC
Migrate to 12.3(11)T
12.2MX
Migrate to 12.3(8)T or later
12.2SU
12.2(14)SU
12.2SW
12.2(19)SW
12.2SY
Migrate to 12.2(17d)SXB or later
12.2SZ
Migrate to 12.2(20)S4
12.2T
12.2(13)T14
12.2(15)T7
12.2XA
Migrate to 12.3 or later
12.2XB
12.2(2)XB18
12.2XC
Migrate to 12.3T or later
12.2XD
Migrate to 12.3 or later
12.2XE
Migrate to 12.3 or later
12.2XF
Migrate to 12.2(15)BC2
12.2XG
Migrate to 12.3 or later
12.2XH
Migrate to 12.3 or later
12.2XI
Migrate to 12.3 or later
12.2XJ
Migrate to 12.3 or later
12.2XK
Migrate to 12.3 or later
12.2XL
Migrate to 12.3 or later
12.2XM
Migrate to 12.3 or later
12.2XN
Migrate to 12.3 or later
12.2XQ
Migrate to 12.3 or later
12.2XR
12.2(15)XR
12.2XS
Migrate to 12.3 or later
12.2XT
Migrate to 12.3 or later
12.2XU
Migrate to 12.3 or later
12.2XV
No plan.
12.2XW
Migrate to 12.3 or later
12.2XZ
Migrate to 12.3 or later
12.2YA
12.2(4)YA8
12.2YB
Migrate to 12.3 or later
12.2YC
Migrate to 12.3 or later
12.2YD
Migrate to 12.3(8)T or later
12.2YE
Migrate to 12.2(18)S or later
12.2YF
Migrate to 12.3 or later
12.2YG
Migrate to 12.3 or later
12.2YH
Migrate to 12.3 or later
12.2YJ
Migrate to 12.3 or later
12.2YL
Migrate to 12.3T or later
12.2YM
Migrate to 12.3T or later
12.2YN
Migrate to 12.3T or later
12.2YO
Migrate to 12.2(17d)SXB or later
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
12.2YU
Migrate to 12.3(2)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
12.2YZ
Migrate to 12.2(20)S4
12.2ZB
Migrate to 12.3T or later
12.2ZC
Migrate to 12.3T or later
12.2ZD
Migrate to 12.3 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
12.2ZJ
Migrate to 12.3T or later
12.2ZL
Migrate to 12.3(7)T or later
12.2ZN
Migrate to 12.3T or later
12.2ZO
Migrate to 12.3 or later
12.2ZP
No plan.
Affected 12.3-Based Release
Rebuild
Maintenance
12.3
12.3(3f)
12.3(5)
12.3B
12.3(5a)B4
12.3BC
12.3(9a)BC
12.3BW
Migrate to 12.3(5a)B or later
12.3T
12.3(2)T5
12.3(4)T7
12.3(7)T
12.3XA
Migrate to 12.3(7)T or later
12.3XB
Migrate to 12.3(8)T or later
12.3XC
Migrate to 12.3(2)XC3 - Availablility date TBD
12.3XD
12.3(4)XD
12.3XE
12.3(2)XE1
12.3XF
12.3(2)XF
12.3XG
12.3(4)XG1
12.3XH
12.3(4)XH
12.3XI
12.3(7)XI
12.3XJ
12.3(7)XJ
12.3XK
12.3(4)XK1
12.3XL
12.3(7)XL
12.3XM
12.3(7)XM
12.3XN
12.3(4)XN
12.3XQ
12.3(4)XQ
12.3XR
12.3(7)XR
12.3XS
12.3(7)XS
12.3XT
12.3(2)XT
12.3XU
12.3(8)XU
12.3XW
12.3(8)XW
12.3XX
12.3(8)XX
12.3XY
12.3(8)XY
12.3YA
12.3(8)YA
12.3YD
12.3(8)YD
12.3YE
12.3(4)YE
12.3YF
12.3(11)YF
12.3YG
12.3(8)YG
12.3YH
12.3(8)YH
When considering software upgrades, please also consult http://www.cisco.com/en/US/products/products_security_advisories_listing.html and any subsequent advisories to determine exposure and a complete upgrade solution.
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 Technical Assistance Center (TAC) for assistance.
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The Cisco PSIRT is not aware of any public announcements or 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
2005-January-28
Clarified wording in Summary section.
Added version 12.2(15)T7 to Software Versions and Fixes table. Removed versions 12.2S, 12.2SX, 12.2SXA, 12.2SXB and 12.2SXD from the Software Versions and Fixes table.
Revision 1.0
2005-January-26
Initial public release.
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