Summary

• 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.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  Only the following products running a vulnerable version of IOS that support MPLS are affected.

  • 2600 and 2800 series routers
    
  • 3600, 3700 and 3800 series routers
    
  • 4500 and 4700 series routers
    
  • 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:

  • Products that are not running Cisco IOS are not vulnerable.
    
  • Products running Cisco IOS versions 12.0 and earlier and 12.1 mainline are not vulnerable.
    
  • 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.

Details

• 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.

Workarounds

• 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.

Fixed Software

• 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.

Exploitation and Public Announcements

• The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050126-les

Revision History

• 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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