Summary

• A vulnerability in the Precision Time Protocol (PTP) feature of Cisco Nexus 5500, 5600, and 6000 Series Switches running 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 a lack of protection against PTP frame flood attacks. An attacker could exploit this vulnerability by sending large streams of malicious IPv4 or IPv6 PTP traffic to the affected device. A successful exploit could allow the attacker to cause a DoS condition, impacting the traffic passing through the 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-20181017-nexus-ptp-dos

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco Nexus 5500, 5600, and 6000 Series Switches that are running a vulnerable release of Cisco NX-OS Software.

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

  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 7.3(2)N1(1) release:

  nx-os# 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) 2002-2017, 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 1.1.7
    Power Sequencer Firmware:
               Module 0: SF-Microcontroller v.0.7, SF-FPGA v.0.6
               …
    FPGA Firmware:
               Module 0: FPGA v.0.0.0.18
  …
    kickstart: version 7.3(2)N1(1)
    system:    version 7.3(2)N1(1)

  
  

  Determining Whether PTP is Enabled on a Device

  Administrators can check to see if the PTP feature is running on an affected device by issuing the following command.

  The show ptp brief command displays the PTP state of all interfaces. A PTP port can be in one of the following three states or disabled:

  • Master: The port is the source of time on the path served by the port.
  • Slave: The port synchronizes with the device on the path on the port that is in the master state.
  • Disabled: PTP is not enabled on this port.
  • Passive: The port is not the master on the path, nor does it synchronize with a master.

  Note: By default, PTP is disabled on the device.

  The following is an example of the show ptp brief output with PTP enabled:

  switch# sh ptp brief 

   
  PTP port status
  -----------------------
  Port         State 
  -------  --------------
  Eth1/3      Enabled

  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:

  • Firepower 2100 Series
  • Firepower 4100 Series Next-Generation Firewall
  • Firepower 9300 Security Appliances
  • MDS 9000 Series Multilayer Switches
  • Nexus 1000V Switch for Microsoft Hyper-V
  • Nexus 1000V Switch for VMware vSphere
  • Nexus 2000 Series Switches
  • Nexus 3000 Series Switches
  • Nexus 3500 Platform Switches
  • Nexus 3600 Platform Switches
  • Nexus 4000 Series Switches
  • Nexus 7000 Series Switches
  • Nexus 9000 Series Fabric Switches in Application-Centric Infrastructure (ACI) mode
  • Nexus 9000 Series Switches in standalone 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
  • UCS 6400 Series Fabric Interconnects

Details

• PTP is a time synchronization protocol for nodes distributed across a network. Its hardware timestamp feature provides greater accuracy than other time synchronization protocols such as the Network Time Protocol (NTP). For more information on how and where to configure PTP on a device, see Cisco Nexus 5000 Series NX-OS System Management Configuration Guide, or contact Cisco TAC for further technical information.

Workarounds

• Customers who are not using the PTP feature can disable it with the no feature ptp command as shown in the following example:

  To enter global configuration mode:

  switch# configure terminal

  Note: Enabling PTP on the switch does not enable PTP on each interface.

  To enable or disable PTP on the device:

  switch(config) # no feature ptp

  See Cisco Nexus 5000 Series NX-OS System Management Configuration Guide for technical assistance regarding PTP.

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

  Customers are advised to upgrade to an appropriate release as indicated in the following table.

  In the table, the left column lists the major releases of Cisco NX-OS Software and the second column indicates the first release that includes the fix for this vulnerability.

  Nexus 5500, 5600, and 6000 Series Switches: CSCvg21830

  Cisco NX-OS Software Major Release	First Fixed Release
  Prior to 6.0	7.3(3)N1(1)
  7.0	7.3(3)N1(1)
  7.1	7.3(3)N1(1)
  7.2	7.3(3)N1(1)
  7.3	7.3(3)N1(1)

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-20181017-nexus-ptp-dos

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2018-October-17

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