Cisco Security Advisory
Cisco Nexus 9000 Series Switches Bidirectional Forwarding Detection Denial of Service Vulnerability
A vulnerability in the rate limiter for Bidirectional Forwarding Detection (BFD) traffic of Cisco NX-OS Software for Cisco Nexus 9000 Series Switches could allow an unauthenticated, remote attacker to cause BFD traffic to be dropped on an affected device.
This vulnerability is due to a logic error in the BFD rate limiter functionality. An attacker could exploit this vulnerability by sending a crafted stream of traffic through the device. A successful exploit could allow the attacker to cause BFD traffic to be dropped, resulting in BFD session flaps. BFD session flaps can cause route instability and dropped traffic, resulting in a denial of service (DoS) condition. This vulnerability applies to both IPv4 and IPv6 traffic.
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:
This advisory is part of the February 2022 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: February 2022 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.
This vulnerability affects Cisco Nexus 9000 Series Switches in standalone NX-OS mode when all of the following conditions are met:
Cisco Nexus 9200 and 9300 Platform Switches
- The device is running a vulnerable version of Cisco NX-OS Software.
- The device has the BFD feature enabled (BFD is disabled by default).
- The device has a Cisco Cloud Scale ASIC installed.
Cisco Nexus 9200 and 9300 Platform Switches are vulnerable from NX-OS Software release 7.0(3)I6(2) to 7.0(3)I7(3) when using a Cisco Cloud Scale ASIC. The Cisco Cloud Scale ASIC PIDs1 supported on these platform switches are as follows:
Cisco Nexus 9500 Series Switches
Cisco Nexus 9500 Series Switches are vulnerable from NX-OS Software release 7.0(3)I6(2) to 9.3(8) and from release 10.1(1) to 10.2(1) when using one of the following Cisco Cloud Scale ASIC PIDs1:
NX-OS Software releases from 10.1(1) to 10.2(2) are also vulnerable when using the following Cisco GX Cloud Scale ASIC PID1:
1. The Cisco Cloud Scale ASIC list of PIDs was accurate at the time of publication. If there is a specific question about a PID, contact the Cisco Technical Assistance Center (TAC).
For additional information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Determine Vulnerable Hardware
Administrators can issue the show module CLI command to view the PID. In the following example, the device is vulnerable because the PID is N9K-C93108TC-FX.
nxos# show module
Mod Ports Module-Type Model Status
--- ----- ------------------------------------- --------------------- ---------
1 54 48x1/10GT + 6x40G/100G Ethernet Modul N9K-C93108TC-FX active *
Determine the BFD Configuration
Step 1: Is the BFD feature enabled?
This vulnerability can only be exploited if the BFD feature is enabled on the device. Administrators can issue the show feature | include bfd CLI command to check the state of the BFD feature. If BFD displays enabled, the feature is enabled on the device.
nxos# show feature | include bfd
bfd 1 enabled
Step 2: Is there an active BFD session?
This vulnerability can be exploited as long as there is at least one active BFD session on the device. Administrators can issue the show bfd neighbors CLI command to check the state of the BFD sessions. If there is any BFD session in Up state, the device is considered vulnerable.
nxos# show bfd neighbors
OurAddr NeighAddr LD/RD RH/RS Holdown(mult) State Int Vrf Type
10.10.20.1 10.10.20.2 1090519044/1090519044 Up 5357(3) Up Eth1/1 default SH
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 1000 Series
- 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 3000 Series Switches
- Nexus 5500 Platform Switches
- Nexus 5600 Platform Switches
- Nexus 6000 Series Switches
- Nexus 7000 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
To determine if this vulnerability is being exploited on the device, administrators can issue the show hardware rate-limiter bfd command at the CLI and review for an excessive amount of Dropped BFD frames.
There are other network events that could cause BFD dropped packets. If there is a high, consistent rate of increasing BFD Dropped packets observed, contact the Cisco TAC for further assistance to determine if this vulnerability is being actively exploited on the device.
nxos# show hardware rate-limiter bfd Units for Config: kilo bits per second Allowed, Dropped & Total: aggregated bytes since last clear counters Module: 1 R-L Class Config Allowed Dropped Total +----------------+--------------+--------------+--------------+-----------+ bfd 10000 640840 5484530000 5485170840
There are no workarounds that address this vulnerability.
Cisco has released free software updates that address the vulnerability described in this advisory. Customers with service contracts that entitle them to regular software updates should obtain security fixes through their usual update channels.
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:
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.
The Cisco Support and Downloads page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool.
When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories 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.
Cisco NX-OS Software
To help customers determine their exposure to vulnerabilities in Cisco NX-OS Software, Cisco provides the Cisco Software Checker to identify any Cisco Security Advisories that impact a specific Cisco NX-OS Software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities described in all the advisories identified (“Combined First Fixed”).
Customers can use the Cisco Software Checker to search advisories in the following ways:
- Choose the software, platform, and one or more releases
- Upload a .txt file that includes a list of specific releases
- Enter the output of the show version command
After initiating a search, customers can customize the search to include all Cisco Security Advisories or one or more specific advisories.
Customers can also use the following form to determine whether a release is affected by any Cisco Security Advisory by choosing the Cisco NX-OS Software and platform and then entering a release-for example, 7.0(3)I7(5) for Cisco Nexus 3000 Series Switches or 14.0(1h) for Cisco NX-OS Software in ACI mode:
By default, the Cisco Software Checker includes results only for vulnerabilities that have a Critical or High Security Impact Rating (SIR). To include results for Medium SIR vulnerabilities, customers can use the Cisco Software Checker and check the Medium check box in the drop-down list under Impact Rating when customizing a search.
Cisco Nexus 9000 Series Switches SMUs
Cisco has released the following SMUs to address this vulnerability. Customers can download the SMUs from the Software Center on Cisco.com.
Cisco NX-OS Software Release Platform SMU Name 7.0(3)I7(10) Nexus 9500 Series Switches1 nxos.CSCvx75912-n9k_ALL-1.0.0-7.0.3.I7.10.lib32_n9000.rpm 9.3(8) Nexus 9500 Series Switches1 nxos.CSCvx75912-n9k_ALL-1.0.0-9.3.8.lib32_n9000.rpm 10.2(2) Nexus 9500 Series Switches2 nxos64-cs.CSCwb07349-1.0.0-10.2.2.lib32_64_n9000.rpm
1. Cisco Nexus 9200 and 9300 Platform Switches are not affected when running this release and do not require an SMU.
2. This SMU is required only if Cisco GX Cloud Scale ASIC PID N9K-X9716D-GX is in use.
For details about downloading and installing SMUs in Cisco NX-OS Software for Cisco Nexus 9000 Series Switches, see the Performing Software Maintenance Upgrades section of the Cisco NX-OS system management configuration guide Cisco Nexus 9000 Series Switches.
For help determining the best Cisco NX-OS Software release for a Cisco Nexus Switch, see 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 Switches
Cisco Nexus 5500 Platform Switches
Cisco Nexus 5600 Platform Switches
Cisco Nexus 6000 Series Switches
Cisco Nexus 7000 Series Switches
Cisco Nexus 9000 Series Switches
Cisco Nexus 9000 Series ACI-Mode Switches
To determine the best release for Cisco UCS Software, see the Recommended Releases documents in the release notes for the device.
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.
This vulnerability was found during the resolution of a Cisco TAC support case.
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 1.2 Added bug ID and fix information specific to Cisco GX Cloud Scale ASIC PID N9K-X9716D-GX. Updated the show command used to verify the active BFD sessions. Affected Products, Fixed Software Final 2022-MAR-23 1.1 Removed sensitive data in Affected Products section. Affected Products Final 2022-FEB-23 1.0 Initial public release. - Final 2022-FEB-23
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