Products & Services

Vulnerable Products

Products Confirmed Not Vulnerable

MVPN architecture introduces an additional set of protocols and procedures that help enable a service provider to support multicast traffic in an MPLS VPN. MVPN allows the transparent transport of IP multicast traffic across the MPLS VPN backbone of a provider and allows a service provider to offer multicast services to MPLS VPN customers.

A vulnerability exists in the implementation of MVPN that allows an attacker to send specially crafted Multicast Distribution Tree (MDT) Data Join messages that can cause the creation of extra multicast states on the core routers. MDT Data Join messages can be sent in unicast or multicast. The vulnerability can also allow leaking multicast traffic from different MPLS VPNs. It is possible to receive multicast traffic from VPNs that are not connected to the same Provider Edge (PE) router. In order to successfully exploit this vulnerability, an attacker needs to know or guess the Border Gateway Protocol (BGP) peering IP address of a remote PE router and the address of the multicast group that is used in other MPLS VPNs.

This vulnerability is documented in the Cisco Bug ID CSCsi01470 (registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2008-1156.

Cisco has provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS Version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding CVSS at

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html .

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at

http://intellishield.cisco.com/security/alertmanager/cvss .

Successful exploitation of the vulnerability can result in the creation of extra multicast states on the core routers or the leaking of multicast traffic from one MPLS VPN to another.

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) names a Cisco IOS release train. If a given release train is vulnerable, then the earliest possible releases that contain the fix (along with the anticipated date of availability for each, if applicable) are listed in the "First Fixed Release" column of the table. The "Recommended Release" column indicates the releases which have fixes for all the published vulnerabilities at the time of this Advisory. 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. Cisco recommends upgrading to a release equal to or later than the release in the "Recommended Releases" column of the table.

The workaround for this vulnerability consists of filtering MDT Data Join packets on the PE device.

The workarounds need to be applied on all Virtual Routing and Forwarding (VRF) interfaces of all PE routers. Otherwise, attackers can target remote PE routers and can still exploit this vulnerability.

Even if only one PE router in the network runs an unfixed version of IOS code, it is vulnerable to packets that come from systems that are connected to remote PE routers. In such a case, workarounds need to be deployed on all PE routers to successfully mitigate this vulnerability.

The mdt data <group> <mask> or mdt data <group> <mask> threshold <n> list <acl> commands do not mitigate this vulnerability.

Filtering Packets to UDP Port 3232

MDT Data Join messages are sent to UDP port 3232. Creating an access-list that filters destination UDP port 3232 and applying it on the VRF interface of the PE router mitigates this vulnerability. Such an access-list looks like this:

access-list 100 deny udp any any eq 3232
access-list 100 permit ip any any

interface Serial 0/0
  ip vrf forwarding <vpn-1>
  ...
  ip access-group 100 in

Note that this access-list can also filter legitimate traffic that is destined to UDP port 3232. In such a case, the access-list can be modified to be more specific by providing individual BGP peer IP addresses. This is explained in the section that follows.

Filtering BGP Peer IP Addresses on the VRF Interface

In order to successfully exploit this vulnerability, an attacker needs to send MDT Data Join messages by spoofing the packets from the IP address of one of the existing iBGP peers. Because MDT Data Join messages are only used between PE routers, the packets from CE devices can safely be filtered.

Creating an access-list that filters iBGP peer IP addresses as source addresses and applying it on the VRF interface of the PE router mitigates this vulnerability. The access-list needs to filter all iBGP peer IP addresses. Such an access-list looks like this example:

access-list 100 deny udp host <ibgp-peer-1> any eq 3232 
access-list 100 deny udp host <ibgp-peer-2> any eq 3232
...
access-list 100 deny udp host <ibgp-peer-n> any eq 3232 
access-list 100 permit ip any any

interface Serial 0/0
  ip vrf forwarding <vpn-1>
  ...
  ip access-group 100 in

Additional mitigation techniques that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory:

http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20080326-mvpn

Cisco has released free software updates that address this vulnerability. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html, or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact psirt@cisco.com or security-alert@cisco.com for software upgrades.

Customers with Service Contracts

Customers with Service Contracts

Customers using Third Party Support Organizations

Customers without Service Contracts

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 Thomas Morin.

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.

This advisory is posted on Cisco's worldwide website at :

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080326-mvpn

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.

• cust-security-announce@cisco.com
  
• first-teams@first.org
  
• bugtraq@securityfocus.com
  
• vulnwatch@vulnwatch.org
  
• cisco@spot.colorado.edu
  
• cisco-nsp@puck.nether.net
  
• full-disclosure@lists.grok.org.uk
  
• comp.dcom.sys.cisco@newsgate.cisco.com
  

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates.

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 website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.