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AUSCERT External Security Bulletin Redistribution
ESB-2020.2945
Cisco FXOS and NX-OS Software Cisco Fabric Services Denial
of Service Vulnerability
27 August 2020
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco FXOS
Cisco NX-OS
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2020-3517
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fxos-nxos-cfs-dos-dAmnymbd
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TITLE: Cisco FXOS and NX-OS Software Cisco Fabric Services Denial of Service Vulnerability
Cisco FXOS and NX-OS Software Cisco Fabric Services Denial of Service
Vulnerability
Priority: High
Advisory ID: cisco-sa-fxos-nxos-cfs-dos-dAmnymbd
First Published: 2020 August 26 16:00 GMT
Last Updated: 2020 August 26 21:23 GMT
Version 1.1: Final
Workarounds: No workarounds available
CVE-2020-3517
CWE-476
CVSS Score:
8.6 AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
Summary
o A vulnerability in the Cisco Fabric Services component of Cisco FXOS
Software and Cisco NX-OS Software could allow an unauthenticated attacker
to cause process crashes, which could result in a denial of service (DoS)
condition on an affected device. The attack vector is configuration
dependent and could be remote or adjacent. For more information about the
attack vector, see the Details section of this advisory.
The vulnerability is due to insufficient error handling when the affected
software parses Cisco Fabric Services messages. An attacker could exploit
this vulnerability by sending malicious Cisco Fabric Services messages to
an affected device. A successful exploit could allow the attacker to cause
a reload of an affected device , which could result 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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-fxos-nxos-cfs-dos-dAmnymbd
This advisory is part of the August 2020 Cisco FXOS and NX-OS Software
Security Advisory Bundled Publication, which includes seven Cisco Security
Advisories that describe seven vulnerabilities. For a complete list of the
advisories and links to them, see Cisco Event Response: August 2020 Cisco
FXOS and NX-OS Software Security Advisory Bundled Publication .
Affected Products
o Vulnerable Products
This vulnerability affects the following Cisco products if they are running
a vulnerable release of Cisco FXOS or NX-OS Software and have Cisco Fabric
Services enabled:
Firepower 4100 Series ( CSCvt46839 )
Firepower 9300 Security Appliances ( CSCvt46839 )
MDS 9000 Series Multilayer Switches ( CSCvt46835 )
Nexus 3000 Series Switches ( CSCvt39630 )
Nexus 5500 Platform Switches ( CSCvt46837 )
Nexus 5600 Platform Switches ( CSCvt46837 )
Nexus 6000 Series Switches ( CSCvt46837 )
Nexus 7000 Series Switches ( CSCvt46835 )
Nexus 9000 Series Switches in standalone NX-OS mode ( CSCvt39630 )
UCS 6200 Series Fabric Interconnects ( CSCvt46838 )
UCS 6300 Series Fabric Interconnects ( CSCvt46838 )
UCS 6400 Series Fabric Interconnects ( CSCvt46877 )
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory.
Determine Whether a Device Has Cisco Fabric Services Enabled
To determine whether a device that is running Cisco FXOS or NX-OS Software
has Cisco Fabric Services enabled, use the show cfs status | include
Distribution command. If the command returns a global Distribution state of
Enabled , the device is vulnerable. If the global Distribution state is
Disabled or this command is not available, the device is not affected by
this vulnerability. The following example shows the output of the show cfs
status | include Distribution command from a device that is vulnerable:
nexus# show cfs status | include Distribution
Distribution : Enabled
Distribution over IP : Enabled
Distribution over Ethernet : Disabled
nexus#
Note: On Cisco UCS Fabric Interconnects, first execute the connect nxos
command to enter the NX-OS CLI, then use the show cfs status | include
Distribution command.
For more information about Cisco Fabric Services and its distribution
status, see the Details 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 1000 Series
Firepower 2100 Series
Nexus 1000 Virtual Edge for VMware vSphere
Nexus 1000V Switch for Microsoft Hyper-V
Nexus 1000V Switch for VMware vSphere
Nexus 9000 Series Fabric Switches in Application Centric Infrastructure
(ACI) mode
Details
o Cisco Fabric Services provides a common infrastructure for distributing and
synchronizing configuration data between Cisco devices that are on the same
network and with virtual port channels (vPCs) or in Virtual Extensible LAN
(VXLAN) deployments. This includes configuration data for applications and
features that are compatible with and enabled to use Cisco Fabric
Services-for example, Distributed Device Alias Services, Network Time
Protocol (NTP), and user and administrator roles.
The vulnerability that is described in this advisory is due to insufficient
error handling when the affected software parses Cisco Fabric Services
messages. Exploitation of this vulnerability does not require any
applications to be enabled to use Cisco Fabric Services. Instead,
exploitation depends on which Cisco Fabric Services distribution types are
configured for a device. In addition, the attack vectors vary based on
which distribution types are configured. If a device is enabled to use more
than one distribution type, the applicable attack vectors for all those
distribution types exist for the device.
Cisco Fabric Services over Fibre Channel
Distribution Distributes data over a Fibre Channel , such as a virtual
storage area network (VSAN)
Enabled by default on Cisco MDS 9000 Series Multilayer
Switches
Enablement
Enabled on Nexus devices if Fibre Channel or Fibre Channel
over Ethernet (FCoE) configuration is present
Attack could occur over Fibre Channel, Fibre Channel over
Ethernet (FCoE), or Fibre Channel over IP (FCIP)
Attack Attack could succeed in the data plane , not the management
Vector plane, of any Fibre Channel port
If no Fibre Channel and no FCoE ports are configured for a
device, this distribution type cannot be used to exploit the
vulnerability
CVSS Attack Adjacent
Vector
Cisco Fabric Services over Ethernet
Distribution Distributes data over an Ethernet network
Enablement Disabled by default
Attack is possible from only a vPC peer or an attacker who
has access to a vPC peer link
Attack Vector
No other peer, neighbor, or network node can be used to
exploit the vulnerability
CVSS Attack Adjacent
Vector
Cisco Fabric Services over IP
Distribution Distributes data over an IPv4 or IPv6 network
Enablement Disabled by default
Attack is possible from any node that has IP network
Attack connectivity to the management interface of a device
Vector
Attack cannot succeed from the data plane
CVSS Attack Network
Vector
Determine the Distribution Status of Cisco Fabric Services
To display configuration information and check the distribution status of
Cisco Fabric Services for a device, use the show cfs status | include
Distribution command in the device CLI, as shown in the following example:
switch# show cfs status | include Distribution
Distribution : Enabled
Distribution over IP : Disabled
Distribution over Ethernet : Disabled
In the preceding example, the Enabled value in the Distribution field of
the command output indicates that Cisco Fabric Services is enabled for the
device and that the device is configured to use the default Cisco Fabric
Services distribution type, which is Cisco Fabric Services over Fibre
Channel. The Disabled value in the Distribution over IP field and the
Distribution over Ethernet field indicates that the device is not
additionally configured to use the Cisco Fabric Services over IP or Cisco
Fabric Services over Ethernet distribution types.
Workarounds
o There are no workarounds that address this vulnerability.
Fixed Software
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/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 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 FXOS Software
In the following table(s), the left column lists Cisco software releases.
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 bundle
and which release includes fixes for those vulnerabilities.
Firepower 4100 Series and Firepower 9300 Security Appliances ^ 1
Cisco FXOS First Fixed Release First Fixed Release for all
Software for This Vulnerabilities Described in the Bundle
Release Vulnerability of Advisories
1.1 1.1.4.179 1.1.4.179
2.0 2.0.1.153 2.0.1.153
2.1 2.1.1.86 2.1.1.86
2.2 2.2.1.70 2.2.1.70
2.3 Not vulnerable Not vulnerable
2.4 Not vulnerable Not vulnerable
2.6 Not vulnerable Not vulnerable
2.7 Not vulnerable Not vulnerable
2.8 Not vulnerable Not vulnerable
1. This vulnerability does not affect releases of Cisco FXOS Software that
have the fix for the Cisco FXOS and NX-OS Software Cisco Fabric Services
Arbitrary Code Execution Vulnerability , which essentially removed support
for Cisco Fabric Services from Cisco FXOS Software.
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:
[Cisco NX-OS Software ] [MDS 9000 Series Multilayer Switches]
[ ] [Check]
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 3000 and 9000 Series Switches Software Maintenance Upgrade
For Cisco Nexus 3000 and 9000 Series Switches, the following software
maintenance upgrade (SMU) is available for Cisco NX-OS Software Release 7.0
(3)I7(8): nxos.CSCvt39630-n9k_ALL-1.0.0-7.0.3.I7.8.lib32_n9000.rpm .
To download the SMU from the Software Center on Cisco.com, do the
following:
1. Click Browse All .
2. Choose IOS and NX-OS Software > NX-OS > NX-OS Software > Switches >
Data Center Switches .
3. Choose the appropriate product and model.
4. Choose NX-OS Software Maintenance Upgrades (SMU) .
5. Choose Release 7.0(3)I7(8) from the left pane of the appropriate
product page.
Note: The SMU filename is
nxos.CSCvt39630-n9k_ALL-1.0.0-7.0.3.I7.8.lib32_n9000.rpm.
SMU Installation Instructions
To install the SMU , copy the SMU to the Bootflash: file system for the
switch and execute the following commands, which activate the fix right
away (this is a hot patch):
1. install add
bootflash:nxos.CSCvt39630-n9k_ALL-1.0.0-7.0.3.I7.8.lib32_n9000.rpm
activate
2. install commit
The following example shows the commands for installing the SMU for Cisco
NX-OS Software Release 7.0(3)I7(8):
nx-os# install add bootflash:nxos.CSCvt39630-n9k_ALL-1.0.0-7.0.3.I7.8.lib32_n9000.rpm activate nx-os# install commit
Note: These instructions apply to only this particular type of SMU.
Cisco UCS Software
In the following table(s), the left column lists Cisco software releases.
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 bundle
and which release includes fixes for those vulnerabilities.
UCS 6200, 6300, and 6400 Series Fabric Interconnects
Cisco UCS First Fixed Release First Fixed Release for All
Software for This Vulnerabilities Described in the Bundle
Release Vulnerability of Advisories
Earlier than Migrate to a fixed Migrate to a fixed release.
3.2 release.
3.2 3.2(3o) 3.2(3o)
4.0 4.0(4i) 4.0(4i)
4.1 4.1(1c) 4.1(1c)
Additional Resources
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.
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.
Source
o This vulnerability was found during internal security testing.
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.
Related to This Advisory
o Cisco Event Response: August 2020 Cisco FXOS and NX-OS Software Security
Advisory Bundled Publication
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-fxos-nxos-cfs-dos-dAmnymbd
Revision History
o +---------+-------------------------+--------------+--------+-------------+
| Version | Description | Section | Status | Date |
+---------+-------------------------+--------------+--------+-------------+
| 1.1 | Fixed Software Checker | Fixed | Final | 2020-AUG-26 |
| | link. | Software | | |
+---------+-------------------------+--------------+--------+-------------+
| 1.0 | Initial public release. | - | Final | 2020-AUG-26 |
+---------+-------------------------+--------------+--------+-------------+
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