A vulnerability in the Cisco Discovery Protocol implementation for Cisco FXOS Software, Cisco IOS XR Software, and Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to cause a reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to a missing check when the affected software processes Cisco Discovery Protocol messages. An attacker could exploit this vulnerability by sending a malicious Cisco Discovery Protocol packet to an affected device. A successful exploit could allow the attacker to exhaust system memory, causing the device to reload. 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). 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-20200205-fxnxos-iosxr-cdp-dos
A vulnerability in the Cisco Discovery Protocol implementation for Cisco FXOS Software, Cisco IOS XR Software, and Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to cause a reload of an affected device, resulting in a denial of service (DoS) condition.
The vulnerability is due to a missing check when the affected software processes Cisco Discovery Protocol messages. An attacker could exploit this vulnerability by sending a malicious Cisco Discovery Protocol packet to an affected device. A successful exploit could allow the attacker to exhaust system memory, causing the device to reload.
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).
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-20200205-fxnxos-iosxr-cdp-dos
This vulnerability affects the following Cisco products if they have Cisco Discovery Protocol enabled both globally and on at least one interface and if they are running a vulnerable release of Cisco FXOS, IOS XR (32-bit or 64-bit), or NX-OS Software:
This vulnerability also affects third-party white box routers if they have Cisco Discovery Protocol enabled both globally and on at least one interface and if they are running a vulnerable release of Cisco IOS XR Software.
Note: Cisco Discovery Protocol is disabled by default in Cisco IOS XR Software. 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 FXOS, IOS XR, and NX-OS Software releases are vulnerable, see the Fixed Software section of this advisory.
Cisco Discovery Protocol is always enabled on the management (mgmt0) port. In Cisco FXOS Software releases earlier than 2.1, Cisco Discovery Protocol is always enabled on all front-panel ports as well.
Administrators can determine whether Cisco Discovery Protocol is enabled on a device by using the show running-config | include cdp 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:
Vulmon
RP/0/RP0/CPU0:ios#show running-config | include cdp
Mon Dec 2 17:00:27.921 UTC
Building configuration...
cdp
cdp
.
.
.
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
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
.
.
.
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:
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.
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.
To disable Cisco Discovery Protocol globally on devices running Cisco IOS XR Software, administrators can use the no cdp command in global configuration mode, as shown in the following example:
RP/0/RP0/CPU0:ios#conf t Mon Dec 2 17:58:08.556 UTC RP/0/RP0/CPU0:ios(config)#no cdp RP/0/RP0/CPU0:ios(config)#exit Uncommitted changes found, commit them before exiting(yes/no/cancel)? [cancel]:yes
To disable Cisco Discovery Protocol a particular interface on a particular device that is running Cisco IOS XR Software, administrators can use the no cdp command in interface configuration mode, as shown in the following example:
RP/0/RP0/CPU0:ios#conf t Mon Dec 2 18:00:08.622 UTC RP/0/RP0/CPU0:ios(config)#interface GigabitEthernet0/0/0/0 RP/0/RP0/CPU0:ios(config-if)#no cdp RP/0/RP0/CPU0:ios(config-if)#end Uncommitted changes found, commit them before exiting(yes/no/cancel)? [cancel]:yes
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.
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.
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 UCS 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#
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 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.
In the following table(s), the left column lists Cisco software releases. The right 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.
| Cisco FXOS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| Earlier than 2.2 |
Migrate to a fixed release |
| 2.2 |
Migrate to a fixed release |
| 2.3 |
2.3.1.173 |
| 2.4 |
Release no. TBD (May 2020) |
| 2.6 |
2.6.1.187 |
| 2.7 |
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 IOS XR Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| Earlier than 6.6 |
Appropriate SMU |
| 6.61 |
6.6.3 or appropriate SMU |
| 7.0 |
7.0.2 (Mar 2020) or appropriate SMU |
| 7.1 |
Not vulnerable |
The following SMUs are also available for Cisco IOS XR Software:
| Cisco IOS XR Software Release |
Platform | SMU Name |
|---|---|---|
| 5.2.5 | NCS6K | ncs6k-5.2.5.CSCvr78185 |
| 6.4.2 | ASR9K-PX |
asr9k-px-6.4.2.CSCvr78185 |
| CRS-PX | hfr-px-6.4.2.CSCvr78185 | |
| 6.5.3 |
ASR9K-PX | asr9k-px-6.5.3.CSCvr78185 |
| ASR9K-X64 |
asr9k-x64-6.5.3.CSCvr78185 | |
| NCS540 |
ncs540-6.5.3.CSCvr78185 | |
| NCS560 |
ncs560-6.6.25.CSCvr78185 |
|
| NCS5K |
ncs5k-6.5.3.CSCvr78185 |
|
| NCS5500 |
ncs5500-6.5.3.CSCvr78185 |
|
| XRV9K |
xrv9k-6.5.3.CSCvr78185 |
|
| 6.6.12 | White box |
iosxrwbd-6.6.12.CSCvr78185 |
| 6.6.25 | NCS560 | ncs560-6.6.25.CSCvr78185 |
| 7.0.1 |
NCS540L | ncs540l-7.0.1.CSCvr78185 |
For details on where to download and how to install SMUs in Cisco IOS XR Software, see the IOS XR Software Maintenance Updates (SMUs) guide.
| Cisco NX-OS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| 5.2 |
6.2(29) |
| 6.2 |
6.2(29) |
| 7.3 |
8.4(1a) |
| 8.1 |
8.4(1a) |
| 8.2 |
8.4(1a) |
| 8.3 |
8.4(1a) |
| 8.4 |
8.4(1a) |
| Cisco NX-OS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| 5.2 |
5.2(1)SV5(1.3) |
| Cisco NX-OS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| Earlier than 5.2 |
No fix available1 |
| 5.2 |
No fix available1 |
| Cisco NX-OS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| Earlier than 5.2 |
5.2(1)SV3(4.1b) |
| 5.2 |
5.2(1)SV3(4.1b) |
| Cisco NX-OS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| Earlier than 7.0(3)I |
7.0(3)I7(8) (Feb 2020) or appropriate SMU1 |
| 7.0(3)I | 7.0(3)I7(8) (Feb 2020) or appropriate SMU1 |
| 7.0(3)F2 |
9.3(2) |
| 9.2 | 9.3(2) |
| 9.3 | 9.3(2) |
SMU Installation Instructions
To download SMUs from the Software Center on Cisco.com, do the following:
Note: The SMU filenames follow this format: CSCvr09175-n9k_ALL-1.0.0-
To install the appropriate SMU, copy the SMU to the Bootflash: file system for the switch and execute the following commands, which activate the fix (this is a hot patch):
The following example shows the commands for installing the SMU for Cisco NX-OS Software Release 7.0(3)I7(6):
nx-os# install add bootflash:CSCvr09175-n9k_ALL-1.0.0-7.0.3.I7.6.lib32_n9000.rpm activate nx-os# install commit
Note: These instructions apply to only this particular type of SMU.
| Cisco NX-OS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| Earlier than 7.1 |
7.3(6)N1(1) |
| 7.1 | 7.3(6)N1(1) |
| 7.3 |
7.3(6)N1(1) |
| Cisco NX-OS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| Earlier than 6.2 |
6.2(24) |
| 6.2 |
6.2(24) |
| 7.2 | 7.3(5)D1(1) |
| 7.3 |
7.3(5)D1(1) |
| 8.0 |
8.2(5) |
| 8.1 |
8.2(5) |
| 8.2 |
8.2(5) |
| 8.3 |
8.4(2) (Mar 2020) or appropriate SMU1 |
| 8.4 |
8.4(2) (Mar 2020) or appropriate SMU1 |
For details on where to download and how to install SMUs in Cisco NX-OS Software for Cisco Nexus 7000 Series Switches, see the Performing Software Maintenance Upgrades chapter of the Cisco Nexus 7000 Series NX-OS System Management Configuration Guide.
| Cisco NX-OS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| Earlier than 13.1 |
13.2(9b) |
| 13.1 |
13.2(9b) |
| 13.2 |
13.2(9b) |
| 14.0 |
14.2(1j) |
| 14.1 |
14.2(1j) |
| 14.2 |
14.2(1j) |
| Cisco UCS Software Release |
First Fixed Release for This Vulnerability |
|---|---|
| Earlier than 3.2 |
3.2(3n) |
| 3.2 | 3.2(3n) |
| 4.0 | 4.0(4g) |
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.
To determine the best release for Cisco UCS, see the Recommended Releases documents in the release notes for the device.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
The Cisco Product Security Incident Response Team (PSIRT) is aware of public announcements about the vulnerability that is described in this advisory. Cisco PSIRT is not aware of any malicious use of this vulnerability.
Cisco would like to thank Barak Hadad of Armis for reporting this vulnerability.
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 |
|---|---|---|---|---|
| 1.3 | Updated available first fixed releases tables. | Fixed Software | Interim | 2020-February-21 |
| 1.2 | Removed FXOS 2.5 which does not exist. Updated FXOS CDP information under Vulnerable Products and Workarounds. | Vulnerable Products, Workarounds, Fixed Software | Interim | 2020-February-07 |
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