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AUSCERT External Security Bulletin Redistribution
ESB-2020.0708
Cisco FXOS and NX-OS Software Cisco Discovery Protocol Arbitrary Code
Execution and Denial of Service Vulnerability
27 February 2020
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco FXOS
Cisco NX-OS
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Execute Arbitrary Code/Commands -- Remote/Unauthenticated
Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2020-3172
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200226-fxos-nxos-cdp
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Cisco FXOS and NX-OS Software Cisco Discovery Protocol Arbitrary Code Execution
and Denial of Service Vulnerability
Priority: High
Advisory ID: cisco-sa-20200226-fxos-nxos-cdp
First Published: 2020 February 26 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
CVE-2020-3172
CWE-20
CVSS Score:
8.8 AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:X/RL:X/RC:X
Summary
o A vulnerability in the Cisco Discovery Protocol feature of Cisco FXOS
Software and Cisco NX-OS Software could allow an unauthenticated, adjacent
attacker to execute arbitrary code as root or cause a denial of service
(DoS) condition on an affected device.
The vulnerability exists because of insufficiently validated Cisco
Discovery Protocol packet headers. An attacker could exploit this
vulnerability by sending a crafted Cisco Discovery Protocol packet to a
Layer 2-adjacent affected device. A successful exploit could allow the
attacker to cause a buffer overflow that could allow the attacker to
execute arbitrary code as root or cause a DoS condition on the affected
device.
Note: Cisco Discovery Protocol is a Layer 2 protocol. To exploit this
vulnerability, an attacker must be in the same broadcast domain as the
affected device (Layer 2 adjacent).
Note: This vulnerability is different from the following Cisco FXOS and
NX-OS Software Cisco Discovery Protocol vulnerabilities that Cisco
announced on Feb. 5, 2020: Cisco FXOS, IOS XR, and NX-OS Software Cisco
Discovery Protocol Denial of Service Vulnerability and Cisco NX-OS Software
Cisco Discovery Protocol Remote Code Execution Vulnerability .
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-20200226-fxos-nxos-cdp
This advisory is part of the February 2020 Cisco FXOS and NX-OS Software
Security Advisory Bundled Publication, which includes six Cisco Security
Advisories that describe six vulnerabilities. For a complete list of the
advisories and links to them, see Cisco Event Response: February 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 Software or Cisco NX-OS Software and if
they are configured to use Cisco Discovery Protocol:
Firepower 4100 Series ( CSCvr37151 )
Firepower 9300 Security Appliances ( CSCvr37151 )
MDS 9000 Series Multilayer Switches ( CSCux07556 )
Nexus 1000 Virtual Edge for VMware vSphere ( CSCvr37146 )
Nexus 1000V Switch for Microsoft Hyper-V ( CSCvr37146 )
Nexus 1000V Switch for VMware vSphere ( CSCvr37146 )
Nexus 3000 Series Switches ( CSCux58226 )
Nexus 5500 Platform Switches ( CSCvr37148 )
Nexus 5600 Platform Switches ( CSCvr37148 )
Nexus 6000 Series Switches ( CSCvr37148 )
Nexus 7000 Series Switches ( CSCux07556 )
Nexus 9000 Series Fabric Switches in Application Centric Infrastructure
(ACI) mode ( CSCvr31410 )
Nexus 9000 Series Switches in standalone NX-OS mode ( CSCux58226 )
UCS 6200 Series Fabric Interconnects ( CSCvr37150 )
UCS 6300 Series Fabric Interconnects ( CSCvr37150 )
Note: Cisco Discovery Protocol is enabled by default both globally and on
all interfaces in Cisco FXOS and NX-OS Software.
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory.
Determine the Status of Cisco Discovery Protocol for Cisco FXOS Software
Cisco Discovery Protocol is always enabled on the management (mgmt0) port.
In Cisco FXOS Software releases earlier than Release 2.1, Cisco Discovery
Protocol is always enabled on all front-panel ports as well.
Determine the Status of Cisco Discovery Protocol on Cisco Nexus Switches
That Are Running Cisco NX-OS Software
Administrators can determine whether Cisco Discovery Protocol is enabled on
a device by using the show running-config cdp all | include "cdp enable"
command in the device CLI. If the command returns at least the following
lines, Cisco Discovery Protocol is enabled globally and on at least one
interface:
nxos# show running-config cdp all | include "cdp enable"
cdp enable
cdp enable
Determine the Status of Cisco Discovery Protocol on Cisco UCS Fabric
Interconnects
Cisco Discovery Protocol is always enabled on Ethernet uplink ports
(network interfaces that connect to upstream switches for network
connectivity), Ethernet port channel members, FCoE uplink ports, and
management ports.
Administrators can determine whether Cisco Discovery Protocol is also
enabled on server ports (interfaces that are presented to the servers in
the Cisco UCS Manager domain) and appliance ports (interfaces that connect
to directly attached NFS storage) on a device by using the show
configuration | egrep "^ scope|enable cdp" command in the device CLI. If
the command returns the enable cdp command under the org scope, Cisco
Discovery Protocol is enabled on server ports, and if the command returns
enable cdp under the eth-storage scope, Cisco Discovery Protocol is enabled
on appliance ports, as shown in the following example:
ucs-fi# show configuration | egrep "^ scope|enable cdp"
.
.
.
scope org
enable cdp
.
.
.
scope eth-storage
enable cdp
.
.
.
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
products:
Firepower 1000 Series
Firepower 2100 Series
UCS 6400 Series Fabric Interconnects
Workarounds
o There are no workarounds that address this vulnerability.
However, customers who do not use the Cisco Discovery Protocol feature can
disable it either globally to fully close the attack vector or on
individual interfaces to reduce the attack surface.
Disable Cisco Discovery Protocol in Cisco FXOS Software
Cisco Discovery Protocol is always enabled and cannot be disabled in Cisco
FXOS Software. In Cisco FXOS Software releases 2.1 and later, Cisco
Discovery Protocol is enabled on the management (mgmt0) port only.
Disable Cisco Discovery Protocol Globally on Cisco Nexus Switches That Are
Running Cisco NX-OS Software
To disable Cisco Discovery Protocol globally on Cisco Nexus Switches that
are running Cisco NX-OS Software, administrators can use the no cdp enable
command in global configuration mode, as shown in the following example:
nxos# conf t
Enter configuration commands, one per line. End with CNTL/Z.
nxos(config)# no cdp enable
nxos(config)# end
nxos# copy running-config startup-config
[########################################] 100%
Copy complete.
Disable Cisco Discovery Protocol on an Interface on Cisco Nexus Switches
That Are Running Cisco NX-OS Software
To disable Cisco Discovery Protocol on an interface on Cisco Nexus Switches
that are running Cisco NX-OS Software, administrators can use the no cdp
enable command in interface configuration mode, as shown in the following
example:
nxos# conf t
Enter configuration commands, one per line. End with CNTL/Z.
nxos(config)# interface Ethernet1/1
nxos(config-if)# no cdp enable
nxos(config-if)# end
nxos# copy running-config startup-config
[########################################] 100%
Copy complete.
Disable Cisco Discovery Protocol on Cisco UCS Fabric Interconnects
Cisco Discovery Protocol cannot be disabled completely on Cisco UCS Fabric
Interconnects.
Cisco Discovery Protocol can be disabled on server ports and appliance
ports on Cisco CS Fabric Interconnects, but it cannot be disabled on
Ethernet uplink ports, Ethernet port channel members, FCoE uplink ports, or
management ports.
To disable Cisco Discovery Protocol on the server ports of a Cisco UCS
Fabric Interconnect, administrators can use the disable cdp command in the
default nw-ctrl-policy in the org scope, as shown in the following example:
ucs-fi# scope org
ucs-fi /org # enter nw-ctrl-policy default
ucs-fi /org/nw-ctrl-policy # disable cdp
ucs-fi /org/nw-ctrl-policy* # exit
ucs-fi /org* # exit
ucs-fi* # commit-buffer
ucs-fi#
To disable Cisco Discovery Protocol on the appliance ports of a Cisco UCS
Fabric Interconnect, administrators can use the disable cdp command in the
default nw-ctrl-policy in the eth-storage scope, as shown in the following
example:
ucs-fi* # scope eth-storage
ucs-fi /eth-storage* # enter nw-ctrl-policy default
ucs-fi /eth-storage/nw-ctrl-policy* # disable cdp
ucs-fi /eth-storage/nw-ctrl-policy* # exit
ucs-fi /eth-storage* # exit
ucs-fi* # commit-buffer
ucs-fi#
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 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.
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: CSCvr37151
Cisco FXOS 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.
2.2 release.
2.2 Migrate to a fixed Migrate to a fixed release.
release.
2.3 Migrate to a fixed Migrate to a fixed release.
release.
2.4 Migrate to a fixed Migrate to a fixed release.
release.
2.6 2.6.1.187 2.6.1.187
2.7 2.7.1.106 2.7.1.106
Note: In Cisco FXOS Software releases 2.1 and later, this vulnerability is
exploitable only via the management (mgmt0) port. In these releases Cisco
Discovery Protocol is never actually enabled on front-panel ports, even if
it is configured.
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 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 and 6300 Series Fabric Interconnects: CSCvr37150
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(3n) 3.2(3n)
4.0 4.0(4g) 4.0(4g)
4.1 Not vulnerable. 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 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, 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 the resolution of a Cisco TAC support
case.
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: February 2020 Cisco FXOS and NX-OS Software Security
Advisory Bundled Publication
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-20200226-fxos-nxos-cdp
Revision History
o +----------+---------------------------+----------+--------+--------------+
| Version | Description | Section | Status | Date |
+----------+---------------------------+----------+--------+--------------+
| 1.0 | Initial public release. | - | Final | 2020-FEB-26 |
+----------+---------------------------+----------+--------+--------------+
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