Summary

• A vulnerability in the fabric infrastructure VLAN connection establishment of the Cisco Nexus 9000 Series Application Centric Infrastructure (ACI) Mode Switch Software could allow an unauthenticated, adjacent attacker to bypass security validations and connect an unauthorized server to the infrastructure VLAN.

  The vulnerability is due to insufficient security requirements during the Link Layer Discovery Protocol (LLDP) setup phase of the infrastructure VLAN. An attacker could exploit this vulnerability by sending a malicious LLDP packet on the adjacent subnet to the Cisco Nexus 9000 Series Switch in ACI mode. A successful exploit could allow the attacker to connect an unauthorized server to the infrastructure VLAN, which is highly privileged. With a connection to the infrastructure VLAN, the attacker can make unauthorized connections to Cisco Application Policy Infrastructure Controller (APIC) services or join other host endpoints.

  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-20190703-n9kaci-bypass

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco Nexus 9000 Series Fabric Switches in ACI mode if they are running a Cisco Nexus 9000 Series ACI Mode Switch Software release prior to 14.1(2g) and are using the default permissive mode setting for fabric secure mode. Refer to the Workarounds section for further information.

  For information about fixed software releases, 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 if they are running the Cisco FXOS or Cisco NX-OS Software:

  • Firepower 2100 Series
  • Firepower 4100 Series
  • Firepower 9300 Security Appliances
  • MDS 9000 Series Multilayer Switches
  • Nexus 1000V Switch for Microsoft Hyper-V
  • Nexus 1000V Switch for VMware vSphere
  • 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
  • UCS 6200 Series Fabric Interconnects
  • UCS 6300 Series Fabric Interconnects
  • UCS 6400 Series Fabric Interconnects

Indicators of Compromise

Workarounds

• If strict mode is configured, this vulnerability cannot be exploited. Strict mode enforces the following further firmware security checks before allowing a connection:

  • Allows only switches with a valid Cisco serial number and Secure Sockets Layer (SSL) certificate.
  • Requires serial number-based authorization.
  • Requires an administrator to manually authorize controllers and switches to join the fabric.

  Administrators can determine if an interface is configured in strict mode by verifying that the system fabric-security-mode strict command is present in the running configuration.

  
  apic# show running-config | grep strict
   system fabric-security-mode strict

  For additional information on configuring strict mode, refer to Configuring Fabric Secure Mode.

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

  This vulnerability is fixed in Cisco Nexus 9000 Series ACI Mode Switch Software Release 14.1(2g) and later.

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

• Cisco would like to thank Oliver Matula from ERNW Enno Rey Netzwerke GmbH in cooperation with ERNW Research GmbH for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190703-n9kaci-bypass

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2019-July-03

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