Summary

• A vulnerability in the implementation of a specific CLI command and the associated Simple Network Management Protocol (SNMP) MIB for Cisco Nexus 3000 and 9000 Series Switches could allow an authenticated, remote attacker to exhaust system memory on an affected device, resulting in a denial of service (DoS) condition.

  The vulnerability is due to the incorrect implementation of the CLI command, resulting in a failure to free all allocated memory upon completion. An attacker could exploit this vulnerability by authenticating to the affected device and repeatedly issuing a specific CLI command or sending a specific SNMP poll request for a specific Object Identifier (OID). A successful exploit could allow the attacker to cause the IP routing process to restart or to cause a device reset, resulting in a DoS condition.

  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-20180620-n3k-n9k-clisnmp

  This advisory is part of the June 2018 Cisco FXOS and NX-OS Software Security Advisory Collection, which includes 24 Cisco Security Advisories that describe 24 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: June 2018 Cisco FXOS and NX-OS Software Security Advisory Collection.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches in standalone NX-OS mode if they 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.

  Checking the Status of SNMP

  Administrators can check whether SNMP is running on a device by using the show running-config snmp command on the device CLI. If the command returns output, SNMP is configured.

  nxos-switch# show running-config snmp
  !Command: show running-config snmp
  .
  .
  .
  snmp-server user admin network-admin auth md5 ***** priv ***** localizedkey
  snmp-server community <removed> group network-admin

  Determining the Cisco NX-OS Software Release

  Administrators can check the release of Cisco NX-OS Software that is running on a device by using the show version command in the device CLI. The following example shows the output of the command for a device that is running Cisco NX-OS Software Release 7.0(3)I5(1):

  nxos-switch# show version
  Cisco Nexus Operating System (NX-OS) Software
  TAC support: http://www.cisco.com/tac
  Copyright (C) 2002-2016, Cisco and/or its affiliates.
  All rights reserved.
  The copyrights to certain works contained in this software are
  owned by other third parties and used and distributed under their own
  licenses, such as open source.  This software is provided "as is," and unless
  otherwise stated, there is no warranty, express or implied, including but not
  limited to warranties of merchantability and fitness for a particular purpose.
  Certain components of this software are licensed under
  the GNU General Public License (GPL) version 2.0 or 
  GNU General Public License (GPL) version 3.0  or the GNU
  Lesser General Public License (LGPL) Version 2.1 or 
  Lesser General Public License (LGPL) Version 2.0. 
  A copy of each such license is available at
  http://www.opensource.org/licenses/gpl-2.0.php and
  http://opensource.org/licenses/gpl-3.0.html and
  http://www.opensource.org/licenses/lgpl-2.1.php and
  http://www.gnu.org/licenses/old-licenses/library.txt.

  Software
    BIOS: version 07.57
    NXOS: version 7.0(3)I5(1) [build 7.0(3)I5(0.9)]
    BIOS compile time:  06/29/2016
    NXOS image file is: bootflash:///nxos.7.0.3.I5.0.9.bin
    NXOS compile time:  8/1/2016 23:00:00 [08/02/2016 00:30:32]
    .
    .
    .

  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 Appliance
  • MDS 9000 Series Multilayer Switches
  • Nexus 1000V Series Switches
  • Nexus 1100 Series Cloud Services Platforms
  • Nexus 2000 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 Fabric Switches in Application Centric Infrastructure (ACI) 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

  Cisco has not investigated whether this vulnerability affects Cisco Nexus 4000 Series Switches, Cisco Nexus 5010 Switches, or Cisco Nexus 5020 Switches because those products have reached end-of-life status. For more information, refer to the End-of-Sale and End-of-Life Announcement for the Cisco Nexus 4000 Series Switch Modules for IBM BladeCenter and the End-of-Sale and End-of-Life Announcement for the Cisco Nexus 5010 and Nexus 5020 Switches.

Details

• The Simple Network Management Protocol (SNMP) is an application-layer protocol that provides a standardized framework and a common language for monitoring and managing devices in a network. It defines a message format for communication between SNMP managers and agents.

  An SNMP agent gathers data from the SNMP MIB, which is the repository of information about device parameters and network data. It also responds to requests from an SNMP manager to get or set data. An SNMP agent contains MIB variables for which values can be requested or changed by an SNMP manager by using get or set operations.

  This vulnerability affects all versions of SNMP supported on the device—Versions 1, 2c, and 3. An attacker could exploit this vulnerability by sending a specific SNMP packet to an affected device via IPv4 or IPv6. Only traffic directed to the affected system can be used to exploit this vulnerability.

  To exploit this vulnerability via SNMP Version 2c or earlier, the attacker must know the SNMP read-only community string for the affected system. A community string is a password that is applied to a device to restrict both read-only and read-write access to the SNMP data on the device. These community strings, as with all passwords, should be chosen carefully to ensure that they are not trivial. They should also be changed at regular intervals and in accordance with network security policies. For example, the strings should be changed when a network administrator changes roles or leaves the organization.

  To exploit this vulnerability via SNMP Version 3, the attacker must have user credentials for the affected system.

  To exploit this vulnerability, the attacker must take time to repeatedly send a specific CLI command or send a specific SNMP poll request for a specific OID to the affected device. Therefore, the attacker cannot immediately exhaust system memory; instead, system resources would be consumed over time.

Indicators of Compromise

• Exploitation of this vulnerability could exhaust system memory. The administrator can monitor the IPFIB process memory usage using the show process memory | include ipfib | PID command. If an ongoing increase is observed in the total amount of memory allocated to the IPFIB process, contact the Cisco Technical Assistance Center (TAC) to help determine if a proactive reboot of the device is needed:
  

  # show process memory | include ipfib | PID
  PID    MemAlloc  MemLimit    MemUsed     StackBase/Ptr      Process
  25179  71282688  1181531648  487817216   ffaf2ca0/ffaf1d9c  ipfib
  26561  352071680 0           905453568   ff9a87a0/ff9a78a0  ipfib
  
  # show processes memory | include ipfib | PID
  PID    MemAlloc  MemLimit    MemUsed     StackBase/Ptr      Process
  25179  71282688  1181531648  487817216   ffaf2ca0/ffaf1d9c  ipfib
  26561  358326272 0           911708160   ff9a87a0/ff9a78a0  ipf

  In addition, exploitation of this vulnerability could cause an affected device to reload and generate an IPFIB core file. To view the IPFIB core file, administrators can use the show core command in the NX-OS CLI. Contact the Cisco 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.

  As a mitigation for the vulnerability that is described in this advisory, administrators can configure an access control list (ACL) on an SNMP community to filter incoming SNMP requests to ensure that SNMP polling is performed only by trusted SNMP clients. In the following example, the device will accept incoming SNMP requests only from a single trusted host, 192.168.1.2:

  switch# show access-list acl_for_snmp
  IPV4 ACL acl_for_snmp
    10 permit udp 192.168.1.2/32 192.168.1.3/32 eq snmp 

  To implement the preceding ACL, administrators can add it to the snmp-server community configuration command:

  switch# show running-config snmp
  !Command: show running-config snmp
  snmp-server community mycompany
   use-acl acl_for_snmp

  For additional information about configuring ACLs to filter incoming SNMP requests, see Filtering SNMP Requests in the NX-OS Configuration Guide.

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 applicable table in this section. To help ensure a complete upgrade solution, consider that this advisory is part of a collection. For a complete list of the advisories in the collection and links to them, see Cisco Event Response: June 2018 Cisco FXOS and NX-OS Software Security Advisory Collection.

  In the following tables, the left column lists releases of Cisco FXOS or NX-OS Software. The center column indicates whether a release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability. The right column indicates whether a release is affected by all the vulnerabilities described in this collection of advisories and which release includes fixes for those vulnerabilities.

  Nexus 3000 Series Switches and Nexus 9000 Series Switches in standalone NX-OS mode: CSCvf23136

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability	First Fixed Release for All Vulnerabilities Described in the Collection of Advisories
  Prior to 7.0(3)I4	Not vulnerable	7.0(3)I7(4)
  7.0(3)I4	7.0(3)I4(8)	7.0(3)I7(4)
  7.0(3)I5	7.0(3)I6(2)	7.0(3)I7(4)
  7.0(3)I6	7.0(3)I6(2)	7.0(3)I7(4)
  7.0(3)I7	7.0(3)I7(1)	7.0(3)I7(4)

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-20180620-n3k-n9k-clisnmp

Revision History

• Version	Description	Section	Status	Date
  1.4	Removed empty table.	Affected Products	Final	2018-July-10
  1.3	Updated the Indicators of Compromise section to describe how to check system memory.	Indicators of Compromise	Final	2018-July-05
  1.2	Metadata update.	—	Final	2018-June-26
  1.1	Metadata update.	—	Final	2018-June-26
  1.0	Initial public release.	—	Final	2018-June-20

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