Summary

• A vulnerability in the Network Time Protocol (NTP) feature of 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 excessive use of system resources when the affected device is logging a drop action for received MODE_PRIVATE (Mode 7) NTP packets. An attacker could exploit this vulnerability by flooding the device with a steady stream of Mode 7 NTP packets. A successful exploit could allow the attacker to cause high CPU and memory usage on the affected device, which could cause internal system processes to restart or cause the affected device to unexpectedly reload.

  Note: The NTP feature is enabled by default.

  Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190828-nxos-ntp-dos

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected the following Cisco products if they were running a vulnerable release of Cisco NX-OS Software and had the NTP feature enabled:
  

  • MDS 9000 Series Multilayer Switches
  • Nexus 3000 Series Switches
  • Nexus 3500 Platform Switches
  • Nexus 3600 Platform 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 standalone NX-OS mode
  • Nexus 9500 R-Series Switching Platform

  For information about which Cisco NX-OS Software releases were vulnerable at the time of publication, see the Fixed Software section of this advisory. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

  The NTP feature is enabled by default. Administrators can use the show running-config | include "feature ntp" command from the Cisco NX-OS CLI to verify if the NTP feature has been manually disabled. If the command returns empty output, the NTP feature is enabled and the device is vulnerable. If the command returns the following output, the NTP feature is disabled and the device is not vulnerable:

  nxos-switch# show running-config | include "feature ntp"
  no feature ntp

  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
  • Firepower 9300 Security Appliances
  • Nexus 1000 Virtual Edge for VMware vSphere
  • Nexus 1000V Switch for Microsoft Hyper-V
  • Nexus 1000V Switch for VMware vSphere
  • Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode
  • UCS 6200 Series Fabric Interconnects
  • UCS 6300 Series Fabric Interconnects
  • UCS 6400 Series Fabric Interconnects

Indicators of Compromise

• Exploitation of this vulnerability could cause the affected device to generate a constant stream of log messages similar to the following:

  USER-3-SYSTEM_MSG: NTP Receive dropping message: Received NTP private mode packet. Drop count: x  - ntpd

  Customers are advised to contact their support organization to review the log messages and determine whether the vulnerability has been exploited on the device.

Workarounds

• Administrators can use the following configuration command on affected devices to reduce the logging level for daemons from the default value of 3 to 2:

  logging level daemon 2

  This would eliminate device exposure to this issue but would cause the affected device to stop logging other syslog messages that might be useful to monitor device operations.

  Customers who are not using the NTP feature can disable it with the no feature ntp configuration command.

Fixed Software

• 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.

  Fixed Releases

  At the time of publication, the release information in the following table(s) was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

  The left column lists Cisco software releases, and the right column indicates whether a release was affected by the vulnerability described in this advisory and which release included the fix for this vulnerability.

  MDS 9000 Series Multilayer Switches: CSCvm51139

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  5.2	Not vulnerable
  6.2	6.2(29)
  7.3	8.3(2)
  8.1	8.3(2)
  8.2	8.3(2)
  8.3	8.3(2)
  8.4	Not vulnerable

  Nexus 3000 Series Switches and Nexus 9000 Series Switches in Standalone NX-OS Mode: CSCvm51138

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  Earlier than 6.0(2)U6	Not vulnerable
  6.0(2)U6	7.0(3)I7(6)
  7.0(3)I	7.0(3)I7(6)
  9.2	9.2(2)
  9.3	Not vulnerable

  Nexus 3500 Platform Switches: CSCvm51142

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  Earlier than 6.0(2)A6	Not vulnerable
  6.0(2)A8	6.0(2)A8(11)
  7.0(3)I7	7.0(3)I7(6)
  9.2	9.2(2)
  9.3	Not vulnerable

  Nexus 3600 Platform Switches and Nexus 9500 R-Series Switching Platform: CSCvm51138

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  7.0(3)F	9.2(2)
  9.2	9.2(2)
  9.3	Not vulnerable

  Nexus 5500, 5600, and 6000 Series Switches: CSCvm35740

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  Earlier than 7.1(4)	Not vulnerable
  7.1(4)	7.3(5)N1(1)
  7.1(5)	7.3(5)N1(1)
  7.2	7.3(5)N1(1)
  7.3	7.3(5)N1(1)

  Nexus 7000 and 7700 Series Switches: CSCvm51139

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  Earlier than 6.2	Not vulnerable
  6.2	7.3(3)D1(1)
  7.2	7.3(3)D1(1)
  7.3	7.3(3)D1(1)
  8.0	8.2(3)
  8.1	8.2(3)
  8.2	8.2(3)
  8.3	8.3(2)
  8.4	Not vulnerable

  
  

  Additional Resources

  For help determining the best Cisco NX-OS Software release for a Cisco Nexus Switch, administrators can refer to the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.

  Cisco MDS Series Switches
  Cisco Nexus 1000V for VMware Switch
  Cisco Nexus 3000 Series and 3500 Series Switches
  Cisco Nexus 5000 Series Switches
  Cisco Nexus 5500 Platform Switches
  Cisco Nexus 6000 Series Switches
  Cisco Nexus 7000 Series Switches
  Cisco Nexus 9000 Series Switches
  Cisco Nexus 9000 Series ACI-Mode Switches

  For help determining the best Cisco NX-OS Software release for Cisco UCS, refer to the Recommended Releases documents in the release notes for the device.

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-20190828-nxos-ntp-dos

Revision History

• Version	Description	Section	Status	Date
  1.1	Updated the MDS fixed release table.	Fixed Software	Final	2019-October-08
  1.0	Initial public release.	-	Final	2019-August-28

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