Summary

• A vulnerability in the DHCP version 6 (DHCPv6) relay feature of Cisco IOS and IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload.
  
  The vulnerability is due to insufficient validation of DHCPv6 relay messages. An attacker could exploit this vulnerability by sending a crafted DHCPv6 relay message to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a denial of service (DoS) condition.
  
  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:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160323-dhcpv6
  
  This advisory is part of the March 23, 2016, release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication, which includes six Cisco Security Advisories that describe six vulnerabilities. All the vulnerabilities have a Security Impact Rating of "High." For a complete list of advisories and links to them, see Cisco Event Response: Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• A DHCPv6 relay agent is used to relay messages between a client and server. A DHCPv6 client locates a DHCPv6 server by using a reserved, link-scoped multicast address. For direct communication between the DHCPv6 client and the DHCPv6 server, both of them must be attached to the same link. However, in situations where ease of management, economy, or scalability is a concern, administrators may choose to configure the DHCPv6 relay feature, which allows a DHCPv6 client to send a message to a DHCPv6 server that is not connected to the same link.

  Vulnerable Products

  This vulnerability affects Cisco devices that are running a vulnerable release of Cisco IOS or Cisco IOS XE Software and have the DHCPv6 relay feature configured on one or more interfaces. By default, the DHCPv6 relay feature is not configured on any interfaces.

  For information about which Cisco IOS and Cisco IOS XE Software releases are vulnerable, see the "Fixed Software" section of this advisory.

  Assessing the DHCPv6 Configuration

  To determine whether the DHCPv6 relay feature is configured on an interface, administrators can use the show running-config | i relay|^interface or show ipv6 dhcp interface command in the command-line interface.

  The following example shows the output of the show running-config command on a router that has the DHCPv6 relay feature configured on the GigabitEthernet0/0/1 interface:

  router#show running-config | i relay|^interface
  .
  .
  .
  interface GigabitEthernet0/0/1
  ipv6 dhcp relay destination 2001:DB8::1941
  .
  .
  .
  

  The following example shows the output of the show ipv6 dhcp interface command on a router that has the DHCPv6 relay feature configured on the GigabitEthernet0/0/1 interface:

  router#show ipv6 dhcp interface
  GigabitEthernet0/0/1 is in relay mode
    Relay destinations:
     2001:DB8::1941

  Determining the Cisco IOS or IOS XE Software Release

  To determine which Cisco IOS Software release is running on a Cisco product, administrators can log in to the device, use the show version command in the command-line interface, and then refer to the system banner that appears. If the device is running Cisco IOS Software, the system banner displays text similar to Cisco Internetwork Operating System Software or Cisco IOS Software. The image name appears in parentheses followed by the Cisco IOS Software release number and release name. Some Cisco devices do not support the show version command or may provide different output.

  The following example identifies a Cisco product that is running Cisco IOS Software Release 15.5(2)T1 with an installed image name of C2951-UNIVERSALK9-M:

  Router> show version 
  Cisco IOS Software, C2951 Software (C2951-UNIVERSALK9-M), Version 15.5(2)T1, RELEASE SOFTWARE (fc1)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2015 by Cisco Systems, Inc.
  Compiled Mon 22-Jun-15 09:32 by prod_rel_team
  .
  .
  .

  For information about the naming and numbering conventions for Cisco IOS Software releases, see White Paper: Cisco IOS and NX-OS Software Reference Guide.

  Products Confirmed Not Vulnerable

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

  Cisco has confirmed that this vulnerability does not affect Cisco IOS XR or Cisco NX-OS Software.

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.

  
  Cisco IOS and IOS XE Software

  To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides a tool, the Cisco IOS Software Checker, that identifies any Cisco Security Advisories that impact a specific software release and the earliest release that fixes the vulnerabilities described in each advisory ("First Fixed"). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities described in all the advisories identified ("Combined First Fixed").

  Customers can use this tool to perform the following tasks:

  • Initiate a search by choosing one or more releases from a drop-down menu or uploading a file from a local system for the tool to parse
  • Enter the output of the show version command for the tool to parse
  • Create a custom search by including all previously published Cisco Security Advisories, a specific advisory, or all advisories in the most recent bundled publication

  To determine whether a release is affected by any published Cisco Security Advisory, use the Cisco IOS Software Checker on Cisco.com or enter a Cisco IOS or IOS XE Software release—for example, 15.1(4)M2 or 3.01.4S—in the following field:

  
  For a mapping of Cisco IOS XE Software releases to Cisco IOS Software releases, refer to the Cisco IOS XE 2 Release Notes, Cisco IOS XE 3S Release Notes, or Cisco IOS XE 3SG Release Notes, depending on the Cisco IOS XE Software release.

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 issue was found during Cisco internal testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160323-dhcpv6

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2016-March-23

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