Summary

• A vulnerability in the Simple Network Management Protocol (SNMP) feature of the Cisco Nexus 4000 Series Switch could allow an authenticated, remote attacker to cause the device to unexpectedly reload, resulting in a denial of service (DoS) condition.
  
  The vulnerability is due to incomplete validation of an SNMP poll request for a specific MIB. An attacker could exploit this vulnerability by sending a specific SNMP poll request to the targeted device. An exploit could allow the attacker to cause the device to reload, 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-n4k-snmp-dos

  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 4000 Series Switches 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.

  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 3000 Series Switches
  • Nexus 3500 Platform Switches
  • Nexus 3600 Platform Switches
  • Nexus 4000 Series Switch
  • 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 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

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.

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

  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 4000 Series Switch: CSCvd34879

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability	First Fixed Release for All Vulnerabilities Described in the Collection of Advisories
  4.1	4.1(2)E1(1s)	4.1(2)E1(1s)

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 internal security testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180620-n4k-snmp-dos

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2018-June-20

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