Summary

• A vulnerability in the implementation of the Simple Network Management Protocol (SNMP) Access Control List (ACL) feature of Cisco NX-OS Software could allow an unauthenticated, remote attacker to perform SNMP polling of an affected device, even if it is configured to deny SNMP traffic.

  The vulnerability is due to an incorrect length check when the configured ACL name is the maximum length, which is 32 ASCII characters. An attacker could exploit this vulnerability by performing SNMP polling of an affected device. A successful exploit could allow the attacker to perform SNMP polling that should have been denied. The attacker has no control of the configuration of the SNMP ACL name.

  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-snmp-bypass

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 with a specific SNMP ACL configured:

  • Nexus 3000 Series Switches
  • Nexus 3500 Platform Switches
  • Nexus 3600 Platform 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.

  Administrators can use the show running-config | include "snmp-server" command to view the configured SNMP ACL for IPv4:

  nxos-switch# show running-config | include "snmp-server"
   snmp-server user  use-ipv4acl 
  

  If this command is present in the running configuration and the ACL name has the maximum length of 32 characters, the device should be considered vulnerable. This applies to IPv6 SNMP ACLs as well.

  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
  • MDS 9000 Series Multilayer Switches
  • Nexus 1000 Virtual Edge for VMware vSphere
  • Nexus 1000V Switch for Microsoft Hyper-V
  • Nexus 1000V Switch for VMware vSphere
  • 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
  • UCS 6200 Series Fabric Interconnects
  • UCS 6300 Series Fabric Interconnects
  • UCS 6400 Series Fabric Interconnects

Details

• 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

• As a workaround, administrators may reconfigure the SNMP ACL name to 31 characters or less.

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.

  Nexus 3000 Series Switches, Nexus 3500 Platform Switches and Nexus 9000 Series Switches in Standalone NX-OS Mode: CSCvo17439

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  Earlier than 7.0(3)	Not vulnerable
  7.0(3)I41	7.0(3)I7(6)1
  7.0(3)I7	7.0(3)I7(6)
  9.2	9.2(3)
  9.3	Not vulnerable

  1. The 7.0(3)I4 code train is not applicable to Nexus 3500 Platform Switches.

  Nexus 3600 Platform Switches and Nexus 9500 R-Series Switching Platform: CSCvo17439

  Cisco NX-OS Software Release	First Fixed Release for This Vulnerability
  7.0(3)F	9.2(3)
  9.2	9.2(3)
  9.3	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 resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190828-nxos-snmp-bypass

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2019-August-28

  Show Less