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AUSCERT External Security Bulletin Redistribution
Cisco Nexus 9000 Series Fabric Switches ACI Mode Fabric
Infrastructure VLAN Unauthorized Access Vulnerability
4 July 2019
AusCERT Security Bulletin Summary
Product: Cisco Nexus 9000 Series Fabric Switches
Publisher: Cisco Systems
Operating System: Network Appliance
Impact/Access: Unauthorised Access -- Remote/Unauthenticated
CVE Names: CVE-2019-1890
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Cisco Nexus 9000 Series Fabric Switches ACI Mode Fabric Infrastructure VLAN
Unauthorized Access Vulnerability
Advisory ID: cisco-sa-20190703-n9kaci-bypass
First Published: 2019 July 3 16:00 GMT
Version 1.0: Final
Workarounds: YesCisco Bug IDs: CSCvp64280
o 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
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:
o 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
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
o 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 .
o 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/
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
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:
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
This vulnerability is fixed in Cisco Nexus 9000 Series ACI Mode Switch
Software Release 14.1(2g) and later.
Exploitation and Public Announcements
o 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.
o Cisco would like to thank Oliver Matula from ERNW Enno Rey Netzwerke GmbH
in cooperation with ERNW Research GmbH for reporting this vulnerability.
Cisco Security Vulnerability Policy
o To learn about Cisco security vulnerability disclosure policies and
publications, see the Security Vulnerability Policy . This document also
contains instructions for obtaining fixed software and receiving security
vulnerability information from Cisco.
| Version | Description | Section | Status | Date |
| 1.0 | Initial public release. | - | Final | 2019-July-03 |
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