Cisco Security Advisory
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The Cisco Catalyst 6500 Series Firewall Services Module (FWSM) contains a Protocol Independent Multicast (PIM) Denial of Service Vulnerability.
Cisco has released software updates that address this vulnerability. There may be workarounds that mitigate this vulnerability. See the "Workarounds" section of this advisory. This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120314-fwsm
Note: The Cisco Adaptive Security Appliance (ASA) and the Cisco Catalyst 6500 ASA Services Module (ASASM) are also affected by this vulnerability.
A separate Cisco Security Advisory has been published to disclose the vulnerabilities that affect the ASA and ASASM. That advisory is available at: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120314-asa
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The Cisco Catalyst 6500 Series Firewall Services Module is affected by this vulnerability. Not all versions of released FWSM Software are affected. Consult the "Software Versions and Fixes" section of this security advisory for more information.
Vulnerable Products
For specific version information, refer to the "Software Versions and Fixes" section of this advisory.
Protocol Independent Multicast Denial of Service Vulnerability
The Cisco FWSM is affected by a vulnerability that may cause affected devices to reload during the processing of a PIM message when multicast routing is enabled. Multicast routing is disabled by default, however when multicast routing is enabled on the Cisco FWSM, PIM is automatically enabled on all interfaces. The following command enables multicast routing:
To verify whether PIM is enabled on an interface use the show pim interface command. The following example shows PIM enabled on the "inside" interface:fwsm(config)# multicast-routingfwsm# sh pim interface
Address Interface PIM Nbr Hello DR DR
Count Intvl Prior
172.16.1.66 inside on 0 30 1 this systemProducts Confirmed Not Vulnerable
With the exception of the Cisco ASA and the Cisco Catalyst 6500 ASA Services Module, no other Cisco products are currently known to be affected by this vulnerability.
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The following section gives additional details about this vulnerability.
Protocol Independent Multicast Denial of Service Vulnerability
Multicast routing is a bandwidth-conserving technology that reduces traffic by simultaneously delivering a single stream of information to multiple recipients.
Protocol Independent Multicast (PIM) is a multicast routing protocol that is independent of any IP routing protocol. PIM can leverage any unicast routing protocols that are in use, including Exterior Gateway Routing Protocol (EIGRP), Open Shortest Path First (OSPF), Border Gateway Protocol (BGP), or static routes, to populate the unicast routing table. PIM uses this unicast routing information to perform the multicast forwarding function, and is IP protocol-independent. Although PIM is called a multicast routing protocol, it actually uses the unicast routing table to perform the Reverse Path Forwarding (RPF) check function instead of building a completely independent multicast routing table. PIM does not send or receive multicast routing updates between routers as do other routing protocols.
A vulnerability exists in the way PIM is implemented that may cause affected devices to reload during the processing of a PIM message when multicast routing is enabled. The vulnerability is due to improper handling of PIM messages. An attacker could exploit this vulnerability by sending a crafted PIM message to the affected system.
This vulnerability is documented in Cisco bug ID CSCtu97367 (registered customers only), and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2012-0356.
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Protocol Independent Multicast Denial of Service Vulnerability
If PIM is required to be enabled, there are no workarounds that mitigate this vulnerability. However, if multicast routing is required but PIM is not used on an interface, PIM can be disabled on the Cisco FWSM interfaces by issuing the no pim interface-level command.
The following example shows the Vlan20 interface, configured as outside, on a Cisco FWSM device with PIM disabled:interface Vlan20
nameif outside
security-level 0
ip address 192.168.1.1 255.255.255.0
no pimTo verify that PIM is disabled on all interfaces, issue the show pim interface command and make sure that for all interfaces the PIM state is set to off. The following example shows a Cisco FWSM with PIM disabled on all interfaces.
fwsm# show pim interface
Address Interface PIM Nbr Hello DR DR
Count Intvl Prior
192.168.1.1 outside off 0 30 1 not elected
172.16.1.66 inside off 0 30 1 not elected
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When considering software upgrades, customers are advised to consult the Cisco Security Advisories and Responses archive at http://www.cisco.com/go/psirt and review subsequent advisories to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.
Protocol Independent Multicast Denial of Service Vulnerability
Vulnerability Major Release
First Fixed Release
Protocol Independent Multicast Denial of Service Vulnerability
2.2
Not Affected
2.3
Not Affected
3.1
Vulnerable: Migrate to 3.2
3.2
3.2(23) Available late March 2012 4.0
Vulnerable: Migrate to 4.1
4.1
4.1(8)
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The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
The vulnerability described in this security advisory was found during the resolution of a customer support case.
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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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Show LessRevision 1.1 2012-March-19 "Workarounds" section: Added a workaround for when PIM is not in use Revision 1.0 2012-March-14 Initial public release
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