Summary

• A vulnerability in the DHCPv6 feature of the Cisco Nexus 9000 Series Fabric Switches in Application-Centric Infrastructure (ACI) Mode could allow an unauthenticated, remote attacker to cause the device to run low on system memory, which could result in a Denial of Service (DoS) condition on an affected system.
  
  The vulnerability is due to improper memory management when DHCPv6 packets are received on an interface of the targeted device. An attacker could exploit this vulnerability by sending a high number of malicious DHCPv6 packets to be processed by an affected device. A successful exploit could allow the attacker to cause the system to run low on memory, which could cause an eventual reboot of an affected device. The vulnerability only applies to IPv6 protocol packets and not for IPv4 protocol packets.

  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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-20180718-nexus-9000-dos

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco Nexus 9000 Series Fabric Switches in ACI Mode running software version 13.0(1k).

  The vulnerability can only be exploited when unicast routing is enabled on the Bridge Domain (BD). DHCP and DHCP relay do not have to be configured for the vulnerability to be exploited.

  Determining the NX-OS Software Release
  
  Administrators can check the version of NX-OS Software running on their device by using the show version command from the device CLI. The following example identifies the 11.2(2) release:

  nxos-n9k-aci# show version
  Cisco Nexus Operating System (NX-OS) Software
  such license is available at
  http://www.opensource.org/licenses/gpl-2.0.php and
  http://www.opensource.org/licenses/lgpl-2.1.php
  Software
    BIOS:      version N/A
    kickstart: version 11.2(2) [build 11.2(1.184)]
    system:    version 11.2(2) [build 11.2(1.184)]

  Determining the APIC Software Release
  
  There is a one-to-one mapping between the software for Cisco Application Policy Infrastructure Controller (APIC) and Cisco Nexus 9000 Series Fabric Switches in ACI Mode. To determine what Cisco APIC release is in use, administrators can remove the leftmost 1 from the Cisco NX-OS Software version number. In the previous example, the Cisco APIC Software version is 1.2(2).

  Determining Whether Unicast Routing is Enabled

  Administrators can check whether unicast routing is enabled on their device by using the following command from the device CLI:

  nxos-n9k-aci# moquery -d uni/tn-ag/BD-bd1 | egrep "unicastRoute"
  unicastRoute             : yes

  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 determined that this vulnerability does not affect the following Cisco products:

  • Firepower 2100 Series
  • Firepower 4100 Series Next-Generation Firewall
  • Firepower 9300 Security Appliance
  • MDS 9000 Series Multilayer Director Switches
  • Nexus 1000V Series Switches
  • Nexus 1100 Series Cloud Services Platforms
  • Nexus 2000 Series Switches
  • Nexus 3000 Series Switches
  • Nexus 3500 Platform Switches
  • Nexus 3600 Platform Switches
  • Nexus 5000 Series Switches
  • Nexus 5500 Platform Switches
  • Nexus 5600 Platform Switches
  • Nexus 7000 Series Switches
  • Nexus 7700 Series Switches
  • Nexus 9000 Series Switches in NX-OS mode
  • Nexus 9500 R-Series Line Cards and Fabric Modules
  • UCS 6100 Series Fabric Interconnects
  • UCS 6200 Series Fabric Interconnects
  • UCS 6300 Series Fabric Interconnects

Indicators of Compromise

• Exploitation of this vulnerability could cause the affected device to reload and write a core file. Contact Cisco Technical Assistance Center (TAC) to review the core file and confirm whether it was due to this vulnerability.

  To verify the current status of the virtual memory usage, administrators can enter the command ps aux | grep 'dhcp_snoop\|VSZ' from the leaf node prompt. If the displayed value exceeds 3 GB, a reboot should be performed to prevent an unplanned device restart. The following example shows a device that has not reached the 3 GB value for the Virtual Memory Size (VSZ):

  nxos-n9k-aci# ps aux | grep 'dhcp_snoop\|VSZ'
  USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
  root     13225  0.0  1.5 1712896 382940 ?      Ssl  Jun26   0:26 /isan/bin/dhcp_snoop
  admin    21444  0.0  0.0   2272   524 pts/0    SN+  11:35   0:00 grep dhcp_snoop\|VSZ

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:
  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.

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

  Fixed Releases

  This vulnerability is fixed in Cisco Nexus 9000 Series Fabric Switches in ACI Mode version 13.0(2k) and later releases.

  The recommended action for all Cisco customers running a device with an affected version is to upgrade to the latest maintenance or latest long-lived version. Cisco suggests that customers visit the following page to determine what fixed release to choose: https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/recommended-release/b_Recommended_Cisco_ACI_Releases.html.

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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-20180718-nexus-9000-dos

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2018-July-18

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