Summary

• A vulnerability in the DHCPv6 relay feature of Cisco Adaptive Security Appliance (ASA) Software could allow an unauthenticated, remote attacker to cause an affected device to reload.
  
  The vulnerability is due to insufficient validation of DHCPv6 packets. An attacker could exploit this vulnerability by sending crafted DHCPv6 packets to an affected device, resulting in a denial of service (DoS) condition.
  
  This vulnerability affects systems configured in routed firewall mode and in single or multiple context mode. Cisco ASA Software is affected by this vulnerability only if the software is configured with the DHCPv6 relay feature. The vulnerability is triggered only by IPv6 traffic.
  
  This vulnerability affects Cisco ASA Software release 9.4.1 only.
  
  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
  
  This advisory is available at the following link: http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160420-asa-dhcpv6

Affected Products

• Cisco ASA Software running on the following products may be affected by this vulnerability:
  

  • Cisco ASA 5500-X Series Next-Generation Firewalls
  • Cisco ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers
  • Cisco Adaptive Security Virtual Appliance (ASAv)

  
  
  Refer to the "Fixed Software" section of this security advisory for more information about the affected releases.

  Vulnerable Products

  Cisco ASA Software is affected by this vulnerability only if the DHCPv6 relay feature is configured. To determine whether the DHCPv6 relay feature is configured, use the show running-config ipv6 dhcprelay command and verify that the feature is enabled on at least one interface.
  
  The following example shows the DHCPv6 relay feature enabled on the interface outside:
  

  asa#show running-config ipv6 dhcprelay
  ipv6 dhcprelay enable outside

  Note: The DHCPv6 relay feature is not configured by default.

  Products Confirmed Not Vulnerable

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

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• Cisco has released free software updates that address the vulnerability described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license.
  http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html
   
  Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.
  
  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 upgrade 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.
  
  Customers Without Service Contracts
  
  Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco Technical Assistance Center (TAC):
  http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html
  
  Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.
  
  Customers should upgrade to an appropriate release as indicated in the following table.
  
  In the table, the left column lists major releases of Cisco ASA Software. The right column indicates whether a major release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability.
  
  

  Cisco ASA Major Release	First Fixed Release
  7.2	Not affected
  8.0	Not affected
  8.1	Not affected
  8.2	Not affected
  8.3	Not affected
  8.4	Not affected
  8.5	Not affected
  8.6	Not affected
  8.7	Not affected
  9.0	Not affected
  9.1	Not affected
  9.2	Not affected
  9.3	Not affected
  9.4	9.4(1.1)
  9.5	Not affected
  9.6	Not affected

  
  
  Software Download
  
  Cisco ASA Software can be downloaded from the Software Center on Cisco.com by visiting http://www.cisco.com/cisco/software/navigator.html.
  
  For Cisco ASA 5500 Series Adaptive Security Appliances and Cisco ASA 5500-X Series Next-Generation Firewall, navigate to the following path. To find interim versions, click All Releases > Interim on the left side of the download page.
  

  Products > Security > Firewalls > Adaptive Security Appliances (ASA) > ASA 5500-X Series Firewalls > <your Cisco ASA model> > Software on Chassis > Adaptive Security Appliance (ASA) Software

  For the Cisco ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers, navigate to the following path. To find interim versions, click All Releases > Interim on the left side of the download page.
  

  Products > Cisco Interfaces and Modules > Services Modules > Catalyst 6500 Series / 7600 Series ASA Services Module > Adaptive Security Appliance (ASA) Software

  For the Cisco Adaptive Security Virtual Appliance (ASAv), navigate to the following path:
  

  Products > Security > Firewalls > Adaptive Security Appliances (ASA) > Adaptive Security Virtual Appliance (ASAv) > Adaptive Security Appliance (ASA) Software

Exploitation and Public Announcements

• 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.

Source

• This vulnerability was found during the resolution of support cases.

URL

• http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160420-asa-dhcpv6

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2016-April-20

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