Summary

• A vulnerability in the IPv6 DHCP version 6 (DHCPv6) relay and server features of Cisco IOS and IOS XE Software could allow an unauthenticated, remote attacker to trigger a denial of service (DoS) condition.

  This vulnerability is due to insufficient validation of data boundaries. An attacker could exploit this vulnerability by sending crafted DHCPv6 messages to an affected device. A successful exploit could allow the attacker to cause the device to reload unexpectedly. 

  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-ios-dhcpv6-dos-44cMvdDK

  This advisory is part of the March 2023 release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: March 2023 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco IOS or IOS XE Software and have IPv6 and the DHCPv6 relay or server feature enabled. IPv6 and DHCPv6 are disabled in Cisco IOS and IOS XE Software by default.

  For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.

  Determine the Device Configuration

  To determine whether a device is enabled to process IPv6 traffic or whether a device has the DHCPv6 relay or server feature enabled, use the instructions below.

  Determine the IPv6 Configuration

  For a device to process IPv6 traffic, both of the following conditions need to be met:

  • IPv6 unicast routing is enabled globally.
  • At least one interface has an IPv6 address configured.

  To determine the IPv6 configuration, use the show running-config CLI command. The following example shows the output on a device that has IPv6 unicast routing enabled globally and that has IPv6 address 2001:DB8:1:40::1/64 configured on interface GigabitEthernet1:

  router#show running-config
  .
  .
  .

  ipv6 unicast-routing
  .
  .
  .
  interface GigabitEthernet1
   .
   .
   .
   ipv6 address 2001:DB8:1:40::1/64
  .
  .
  .

  If either of the following is true, the device is not affected by this vulnerability:

  • IPv6 traffic processing is not enabled using the ipv6 unicast-routing configuration command.
  • No interface has an IPv6 address configured using the ipv6 address configuration command.

  Determine the DHCPv6 Relay Configuration

  To determine whether the DHCPv6 relay feature is enabled, use the show running-config | include ipv6 dhcp relay CLI command. The following example shows the output on a device that has the DHCPv6 relay feature enabled under one interface:

  router#show running-config | include ipv6 dhcp relay
   ipv6 dhcp relay destination 2001:DB8:2:40::10

  If this command returns empty output, the DHCPv6 relay feature is not enabled.

  Determine the DHCPv6 Server Configuration

  When both of the following conditions are met, the DHCPv6 server feature is enabled:

  • A DHCPv6 address pool is configured globally.
  • The DHCPv6 server feature is enabled on at least one interface and points to an existing DHCPv6 pool.

  To determine whether the DHCPv6 server feature is enabled, use the show running-config CLI command. The following example shows the output on a device that has DHCPv6 pool DHCPv6_POOL configured globally and the DHCPv6 server feature enabled under interface GigabitEthernet1:

  router#show running-config
  .
  .
  .

  ipv6 dhcp pool DHCPv6_POOL
  .
  .
  .
  interface GigabitEthernet1
   .
   .
   .
   ipv6 dhcp server DHCPv6_POOL
  .
  .
  .

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

  Cisco has confirmed that this vulnerability does not affect the following Cisco products:

  • Adaptive Security Appliance (ASA) Software
  • Firepower Management Center (FMC) Software
  • Firepower Threat Defense (FTD) Software
  • FXOS Software
  • IOS XR Software
  • Meraki products
  • Next-Generation Intrusion Prevention System (NGIPS) Software
  • 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 with service contracts that entitle them to regular software updates should obtain security fixes through their usual update channels.

  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:
  https://www.cisco.com/c/en/us/products/end-user-license-agreement.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.

  The Cisco Support and Downloads page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool.

  When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories page, 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.

  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 TAC: https://www.cisco.com/c/en/us/support/web/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 the Cisco Software Checker. This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies (“Combined First Fixed”). 

  To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to determine whether a release is affected by any Cisco Security Advisory. To use the form, follow these steps:

  1. Choose which advisories the tool will search—only this advisory, only advisories with a Critical or High Security Impact Rating (SIR), or all advisories.
  2. Enter a release number—for example, 15.9(3)M2 or 17.3.3.
  3. Click Check.

   

  Only this advisory All Critical and High advisories All advisories

   

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 a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-dhcpv6-dos-44cMvdDK

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2023-MAR-22

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