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Cisco Security Advisory

Cisco IOS MPLS VPN May Leak Information

Medium
Advisory ID:
cisco-sa-20080924-vpn
First Published:
2008 September 24 16:00 GMT
Version 1.2:
Final
Workarounds:
See below
Cisco Bug IDs:
CSCec12299
CSCee83237
CVE-2008-3803
IntelliShield
CVSS Score:
Base 5.1, Temporal 4.2Click Icon to Copy Verbose Score
AV:N/AC:H/Au:N/C:P/I:P/A:P/E:F/RL:OF/RC:C
CVE-2008-3803
IntelliShield

Summary

Affected Products

  • Products running Cisco IOS versions 12.0S, 12.2, 12.3 or 12.4 and configured for MPLS VPNs or VRF Lite are potentially affected.

    Cisco IOS releases based on 12.1 are not affected.

    Vulnerable Products

    Cisco IOS devices are vulnerable if they are configured for MPLS VPN or VRF Lite and have a BGP session between the CE and PE devices, and process extended communities. If a device is configured for MPLS VPN or VRF Lite the command address-family ipv4 vrf <vrf-name> or address-family ipv6 vrf <vrf-name> will be present in the device configuration.

    The following shows a command executed on a device configured for MPLS VPN:

    router#show running-config | include address-family [ipv4|ipv6]

address-family ipv4 vrf

    The following shows a PE device configured for an IPv4 BGP session between the PE and the CE:

    router bgp 
 address-family ipv4 vrf one
 neighbor  remote-as < Remote AS>
 neighbor  activate

    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 that is running Cisco IOS release 12.4(11)T2:

    Router#show version
Cisco IOS Software, 7200 Software (C7200-ADVSECURITYK9-M), Version 12.4(11)T2, RELEASE SOFTWARE (fc4)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Tue 01-May-07 04:19 by prod_rel_team

    Additional information on the Cisco IOS release naming conventions can be found on the document entitled "White Paper: Cisco IOS Reference Guide", which is available at http://www.cisco.com/web/about/security/intelligence/ios-ref.html

    Products Confirmed Not Vulnerable

    Cisco products not configured for MPLS VPNs or VRF Lite are unaffected by this vulnerability.

    Cisco products that do not run IOS are unaffected by this vulnerability.

    Cisco IOS-XR is not affected.

    No other Cisco products are currently known to be affected by this vulnerability.

Details

  • MPLS VPNs allow for the creation of 'virtual networks' that customers can use to segregate traffic into multiple, isolated VPNs. Traffic within each MPLS VPN is kept separate from the others, thereby maintaining a virtual private network.

    More information on MPLS and MPLS VPNs is available at the following link:

    http://www.cisco.com/en/US/products/ps6557/products_ios_technology_home.html

    A bug exists when processing extended communities with MPLS VPNs. If extended communities are used, MPLS VPN may incorrectly use a corrupted route target (RT) to forward traffic. If this occurs, traffic can leak from one MPLS VPN to another.

    This vulnerability exists whenever an affected PE device has a BGP session running in the MPLS VPN Virtual Routing and Forwarding (VRF). The following two examples of this scenario are the most common:

    1) MPLS VPN configuration with BGP running inside the VRF between the PE and CE devices.

    2) MPLS Inter-AS option A with BGP running between the Autonomous System Border Routers (ASBR).

    The mitigation in the Workarounds section filters extended communities on a PE device, preventing them from being received by devices configured for MPLS VPN.

    This vulnerability was introduced with Cisco bug ID CSCee83237. Cisco IOS images that do not include CSCee83237 are not vulnerable to this issue.

    It is important to note that this condition cannot be triggered by an attacker and that the condition does not provide ways to determine the flow of traffic between VPNs.

    This vulnerability is documented in the Cisco Bug ID CSCec12299 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2008-3803.

Workarounds

  • Customers running versions of Cisco IOS that support filtering of extended communities can prevent the corruption of the route target (RT) by applying a BGP route-map that removes RT entries on inbound BGP sessions.

    The following configuration example applied in the ipv4 address family of a PE device removes extended communities from the CE router:

    router bgp <Local AS>
 address-family ipv4 vrf one
 neighbor <neighbor IP> remote-as <Remote AS>
 neighbor <neighbor IP> activate
 neighbor <neighbor IP> route-map FILTER in
 exit-address-family
!
ip extcommunity-list 100 permit _RT.*_
!
!
route-map FILTER permit 10
 set extcomm-list 100 delete
!

    The following configuration example applied in the ipv6 address family of a PE device removes extended communities from the CE router:

    router bgp <Local AS>
 address-family ipv6 vrf one
 neighbor <neighbor IP> remote-as <Remote AS>
 neighbor <neighbor IP> activate
 neighbor <neighbor IP> route-map FILTER in
 exit-address-family
!
ip extcommunity-list 100 permit _RT.*_
!
!
route-map FILTER permit 10
 set extcomm-list 100 delete
!

    Note: The capability of filtering extended communities is only available in certain 12.0S and 12.2S based Cisco IOS releases.

    BGP session between the PE and the CE needs to cleared to make this configuration change effective.

Fixed Software

Exploitation and Public Announcements

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

    This vulnerability was reported to Cisco by a customer.

    This vulnerability cannot be deterministically triggered by an attacker.

Cisco Security Vulnerability Policy

  • 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 History

  • Revision 1.2

    2009-April-16

    Removed references to the combined software table, as it is now outdated.

    Revision 1.1

    2008-Nov-19

    Updated configuration examples in Workarounds section.

    Revision 1.0

    2008-Sep-24

    Initial public release.

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Cisco Security Vulnerability Policy

  • 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.

Subscribe to Cisco Security Notifications

Related to This Advisory