Summary

• A vulnerability in the implementation of the DHCPv4 relay agent in Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.
  
  The vulnerability is due to improper validation of malformed DHCPv4 packets. An attacker could exploit this vulnerability by sending malformed DHCPv4 packets to an affected device. An exploit could allow the attacker to cause the DHCP process or device to crash.
  
  

  This vulnerability can be exploited using IPv4 packets only. The vulnerability can be triggered by malformed DHCP packets processed by a DHCP relay agent listening on the device, using the IPv4 broadcast address or IPv4 unicast address of any interface configured on a device.
  

  
  

  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-20161005-dhcp2

Affected Products

• Vulnerable Products

  The following Cisco products are vulnerable if they are running Cisco NX-OS System Software that is configured for DHCP:
  

  • Nexus 2000 Series Fabric Extenders
  • Nexus 3000 Series Switches
  • Nexus 3500 Platform Switches
  • Nexus 5000 Series Switches
  • Nexus 5500 Platform Switches
  • Nexus 5600 Platform Switches
  • Nexus 6000 Series Switches
  • Nexus 7000 Series Switches
  • Nexus 7700 Series Switches
  • Nexus 9000 Series Switches in Application Centric Infrastructure (ACI) mode
  • Nexus 9000 Series Switches in NX-OS mode

  This vulnerability affects only devices configured with the DHCPv4 process enabled and configured as a DHCPv4 relay agent.
  
  To determine whether a Cisco Nexus device running a vulnerable version of Cisco NX-OS Software is configured as a DHCPv4 relay agent, administrators can use the show running | include dhcp command from the Cisco NX-OS command-line interface (CLI) and verify that the feature is enabled.
  
  The following example shows that the DHCP relay feature is enabled on a device running Cisco NX-OS Software that is configured to relay DHCP requests to a DHCP server with the IPv4 address 192.168.0.1:
  

  # show running | include dhcp
  feature dhcp 
  ip dhcp relay 
  ip dhcp relay address 192.168.0.1

  To determine whether a vulnerable version is running on a Cisco NX-OS device, administrators can use the show version command from the NX-OS CLI. The following example shows the results for a Cisco Nexus 5000 Series Switch running Cisco NX-OS Software version 5.2(1)N1(1b):

  # show version
  Cisco Nexus Operating System (NX-OS) Software
  TAC support: http://www.cisco.com/tac
  Documents: http://www.cisco.com/en/US/products/ps9372/tsd_products_support_series_home.html
  Copyright (c) 2002-2012, Cisco Systems, Inc. All rights reserved.
  The copyrights to certain works contained herein are owned by
  other third parties and are used and distributed under license.
  Some parts of this software are covered under the GNU Public
  License. A copy of the license is available at
  http://www.gnu.org/licenses/gpl.html.
  
  Software
   BIOS:      version 3.6.0
   loader:     version N/A
   kickstart: version 5.2(1)N1(1b)
   system:    version 5.2(1)N1(1b)

  Products Confirmed Not Vulnerable

  No other Cisco products are currently known to be affected by this vulnerability.
  
  The following products are not affected by this vulnerability:
  

  • Multilayer Director Switches
  • Nexus 1000V Series Switches
  • Nexus 4000 Series Switches
  • Unified Computing System (UCS) 6100 Series Fabric Interconnects
  • UCS 6200 Series Fabric Interconnects

Indicators of Compromise

• Exploitation of this vulnerability will cause the affected device to reload and generate a DHCP process core file. Contact the Cisco Technical Assistance Center (TAC) to review the core file and determine whether the device has been compromised by exploitation of 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.
  

  
  Fixed Releases
  
  Customers should upgrade to an appropriate release as indicated in the applicable table in this section. To help ensure a complete upgrade solution, consider that this advisory is part of a collection that includes the following advisories:
  
  cisco-sa-20161005-bgp: Cisco NX-OS Border Gateway Protocol Denial of Service Vulnerability
  cisco-sa-20161005-dhcp1: Cisco NX-OS Software Crafted DHCPv4 Packet Denial of Service Vulnerability
  cisco-sa-20161005-dhcp2: Cisco NX-OS Software Malformed DHCPv4 Packet Denial of Service Vulnerability
  cisco-sa-20161005-nxaaa: Cisco NX-OS Software-Based Products Authentication, Authorization, and Accounting Bypass Vulnerability
  cisco-sa-20161005-otv: Cisco Nexus 7000 and 7700 Series Switches Overlay Transport Virtualization Buffer Overflow Vulnerability
  
  In the following table, the left column lists major releases of Cisco NX-OS Software. The center column indicates whether a major release is affected by the vulnerability described in this advisory and the first minor release that includes the fix for this vulnerability. The right column indicates whether a major release is affected by all the vulnerabilities described in this collection of advisories and which release includes fixes for those vulnerabilities.
  
  Cisco Nexus 3000 Series Switches: CSCus21733
  
  

  Cisco NX-OS Software Major Release - Nexus 3000 Series Switches	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  Prior to 6.0	Affected; migrate to 6.0(2)U6(6)	6.0(2)U6(7)
  6.0	6.0(2)U6(6)	6.0(2)U6(7)
  7.0	7.0(3)I2(2b) or 7.0(3)I3(1)	7.0(3)I4(1)

  
  Cisco Nexus 3500 Platform Switches: CSCus21733
   
  

  Cisco NX-OS Software Major Release - Nexus 3500 Platform Switches	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  Prior to 6.0	Affected; migrate to 6.0(2)A6(6)	6.0(2)A8(1)
  6.0	6.0(2)A6(6)	6.0(2)A8(1)

  
  Cisco Nexus 2000, 5000, 5500, 5600, and 6000 Series Switches: CSCus21739
  
  

  Cisco NX-OS Software Major Release - Nexus 5000 Series Switches	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  Prior to 5.2	Affected; migrate to 5.2(1)N1(9)	5.2(1)N1(9a)
  5.2	5.2(1)N1(9)	5.2(1)N1(9a)

  
  

  Cisco NX-OS Software  Major Release - Nexus 2000, 5500 Platform, 5600 Platform, and 6000 Series Switches	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  Prior to 5.2	Affected; migrate to 5.2(1)N1(9)	7.1(4)N1(1)
  5.2	5.2(1)N1(9)	7.1(4)N1(1)
  6.0	6.0(2)N2(7)	7.1(4)N1(1)
  7.0	7.0(6)N1(1)	7.1(4)N1(1)
  7.1	7.1(1)N1(1)	7.1(4)N1(1)
  7.2	7.2(0)N1(1)	7.2(2)N1(1)
  7.3	7.3(0)N1(1)	7.3(0)N1(1)

  
  Cisco Nexus 7000 and 7700 Series Switches: CSCuq39250
  
  

  Cisco NX-OS Software Major Release - Nexus 7000 and 7700 Series Switches	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  Prior to 5.2	Affected; migrate to 6.2(16)	7.2(2)D1(1)
  5.2	Affected; migrate to 6.2(16)	7.2(2)D1(1)
  6.0	Affected; migrate to 6.2(16)	7.2(2)D1(1)
  6.1	Affected; migrate to 6.2(16)	7.2(2)D1(1)
  6.2	6.2(16)	7.2(2)D1(1)
  7.2	7.2(0)D1(1)	7.2(2)D1(1)
  7.3	7.3(0)D1(1)	7.3(1)D1(1)

  
  Cisco Nexus 9000 Series Switches in ACI Mode: CSCut76171
  
  

  Cisco NX-OS Software Major Release - Nexus 9000 Series Switches in ACI Mode	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  11.0	Affected; migrate to 11.1	11.1(1j)
  11.1	11.1	11.1(1j)
  11.2	Not vulnerable	11.1(1j)

  
  Cisco Nexus 9000 Series Switches in NX-OS Mode: CSCux67182
  
  

  Cisco NX-OS Software Major Release - Nexus 9000 Series Switches in NX-OS Mode	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  6.1	Affected; migrate to 7.0(3)I2(2b) or 7.0(3)I3(1)	7.0(3)I4(1)
  7.0	7.0(3)I2(2b) or 7.0(3)I3(1)	7.0(3)I4(1)

  
  Release Recommendations
  
  For additional assistance in determining the best NX-OS Software release for a Cisco Nexus Switch, refer to the recommended release document for the switch:

  • Cisco Nexus 3000 Series and 3500 Platform Switches
  • Cisco Nexus 5000 Series Switches
  • Cisco Nexus 5500 Platform Switches
  • Cisco Nexus 5600 Platform Switches
  • Cisco Nexus 6000 Series Switches
  • Cisco Nexus 7000 Series Switches
  • Cisco Nexus 9000 Series Switches

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 support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20161005-dhcp2

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2016-October-05

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