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AUSCERT External Security Bulletin Redistribution
ESB-2021.3184
Multiple Cisco Operating Systems Unidirectional Link
Detection Denial of Service Vulnerability
23 September 2021
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AusCERT Security Bulletin Summary
---------------------------------
Product: FXOS Software
IOS Software
IOS XE Software
IOS XR Software
NX-OS Software
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2021-34714
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-nxos-xr-udld-dos-W5hGHgtQ
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Multiple Cisco Operating Systems Unidirectional Link Detection Denial of
Service Vulnerability
Priority: Medium
Advisory ID: cisco-sa-ios-nxos-xr-udld-dos-W5hGHgtQ
First Published: 2021 September 22 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCvw22670 CSCvw26126 CSCvw26127 CSCvw26129 CSCvw26130
CSCvw26152 CSCvw46194 CSCvw46239
CVE Names: CVE-2021-34714
CWEs: CWE-20
Summary
o A vulnerability in the Unidirectional Link Detection (UDLD) feature of
Cisco FXOS Software, Cisco IOS Software, Cisco IOS XE Software, Cisco IOS
XR Software, and Cisco NX-OS Software could allow an unauthenticated,
adjacent attacker to cause an affected device to reload.
This vulnerability is due to improper input validation of the UDLD packets.
An attacker could exploit this vulnerability by sending specifically
crafted UDLD packets to an affected device. A successful exploit could
allow the attacker to cause the affected device to reload, resulting in a
denial of service (DoS) condition.
Note: The UDLD feature is disabled by default, and the conditions to
exploit this vulnerability are strict. An attacker must have full control
of a directly connected device. On Cisco IOS XR devices, the impact is
limited to the reload of the UDLD process.
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-ios-nxos-xr-udld-dos-W5hGHgtQ
This advisory is part of the September 2021 release of the Cisco IOS and
IOS XE Software Security Advisory Bundled Publication. For a complete list
of the advisories and links to them, see Cisco Event Response: September
2021 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled
Publication.
Affected Products
o Vulnerable Products
At the time of publication, this vulnerability affected Cisco devices if
they were running a vulnerable release of the following Cisco software and
had the UDLD feature enabled:
IOS Software ( CSCvw46194 )
IOS XE Software ( CSCvw46194 )
IOS XR software ( CSCvw46239 )
At the time of publication, this vulnerability also affected the following
Cisco products if they were running a vulnerable release of Cisco FXOS or
NX-OS Software and had the UDLD feature enabled:
Firepower 4100 Series ( CSCvw26130 ) ^ 1
Firepower 9300 Security Appliances ( CSCvw26130 ) ^ 1
MDS 9000 Series Multilayer Switches ( CSCvw26126 )
Nexus 3000 Series Switches ( CSCvw22670 )
Nexus 5500 Platform Switches ( CSCvw26127 )
Nexus 5600 Platform Switches ( CSCvw26127 )
Nexus 6000 Series Switches ( CSCvw26127 )
Nexus 7000 Series Switches ( CSCvw26126 )
Nexus 9000 Series Switches in standalone NX-OS mode ( CSCvw22670 )
UCS 6200 Series Fabric Interconnects ( CSCvw26129 )
UCS 6300 Series Fabric Interconnects ( CSCvw26129 )
UCS 6400 Series Fabric Interconnects ( CSCvw26152 )
1. Firepower 4100 and 9300 products do not officially support UDLD;
however, the CLI includes commands to enable it. These products could be
vulnerable only if UDLD has been enabled in error. In such cases,
administrators are advised to disable UDLD to fully eliminate exposure to
this vulnerability.
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory.
Determine the Status of the UDLD Feature
To determine whether the UDLD feature is enabled on a device, follow the
product-specific instructions below:
Cisco FXOS Software and UCS Fabric Interconnects
Use the scope org command followed by the show udld-link-policy command at
the device CLI. The command output will display either Enabled or Disabled
under Admin State for the default and for any manually configured UDLD link
policy. The following example shows the command output on a device that has
UDLD disabled:
fxos# scope org
fxos# show udld-link-policy
UDLD link policy:
Name Admin State UDLD mode
---------- ----------- ---------
default Disabled Normal
Cisco IOS and IOS XE Software
Use the show udld | include "state: Enabled" command at the device CLI. If
the command returns output, the UDLD feature is configured on some
interfaces of the device. The following example shows the command output on
a device that has UDLD enabled:
Router# show udld | include "state: Enabled"
Port enable operational state: Enabled / in aggressive mode
Cisco IOS XR Software
Use the show ethernet udld interfaces brief command at the device CLI. If
the command returns output, the UDLD feature is configured on some
interfaces of the device. The following example shows the command output on
a device that has UDLD enabled:
RP/0/RSP0/CPU0:router# show ethernet udld interfaces brief
Port State Neighbor Device N'bor port
------------- -------------- ------------------------------- -------------
Gi0/1/0/1 Bidirectional london-xr22.cisco.com Gi3/12/0/24
Gi0/1/0/2 Bidirectional [2 neighbors] -
Gi0/1/0/3 Unknown - -
Gi0/1/0/4 Unidirectional sj-ios25.cisco.com Gi3/5
Te0/12/0/10 Admin Down - -
Te0/12/0/11 N'bor Mismatch long-device.cisco.com LongPortNam>>
Cisco NX-OS Software
Use the show running-config | include "feature udld" command at the device
CLI. If the command returns output, the UDLD feature is configured on the
device. The following example shows the command output on a device that has
UDLD enabled:
nxos# show running-config | include "feature udld"
feature udld
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
Meraki products
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
Workarounds
o There are no workarounds that address this vulnerability.
Fixed Software
o 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.
Cisco FXOS Software
At the time of publication, the release information in the following table
(s) was accurate. See the Details section in the bug ID(s) at the top of
this advisory for the most complete and current information.
The left column lists Cisco software releases, and the right column
indicates whether a release was affected by the vulnerability described in
this advisory and which release included the fix for this vulnerability.
Firepower 4100 Series and Firepower 9300 Security Appliances
Cisco FXOS Software Release First Fixed Release for this Vulnerability
2.2 2.2.2.148 ^1
2.3 2.3.1.216 ^1
2.4 2.4.1.273 ^1
2.6 2.6.1.224 ^1
2.7 2.7.1.143 ^1
2.8 2.8.1.143 ^1
2.9 2.9.1.135 ^1
2.10 Not vulnerable
1. Firepower 4100and 9300 products do not officially support UDLD; however,
the CLI includes commands to enable it. These products could be vulnerable
only if UDLD has been enabled in error. In such cases, administrators are
advised to disable UDLD to fully eliminate exposure to this vulnerability.
Cisco IOS and IOS XE Software
To help customers determine their exposure to vulnerabilities in Cisco IOS
and IOS XE Software, Cisco provides the Cisco Software Checker to identify
any Cisco Security Advisories that impact a specific software release and
the earliest release that fixes the vulnerabilities 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 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, a specific advisory, or all advisories in
the most recent bundled publication.
Customers can also use the following form to determine whether a release is
affected by any Cisco Security Advisory by entering a Cisco IOS or IOS XE
Software release-for example, 15.1(4)M2 or 3.13.8S :
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 on Cisco.com and check the Medium check box in the
drop-down list under Impact Rating when customizing a search.
Cisco IOS XR Software
At the time of publication, the release information in the following table
(s) was accurate. See the Details section in the bug ID(s) at the top of
this advisory for the most complete and current information, including SMU
availability.
The left column lists Cisco software releases, and the right column
indicates whether a release was affected by the vulnerability described in
this advisory and which release included the fix for this vulnerability.
Cisco IOS XR Software Release First Fixed Release for this Vulnerability
6.6 Vulnerable; migrate to a fixed release.
6.7 6.7.4
6.8 6.8.1
7.2 7.2.2
7.3 7.3.1, 7.3.15
7.4 7.4.1
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 UCS Software
At the time of publication, the release information in the following table
(s) was accurate. See the Details section in the bug ID(s) at the top of
this advisory for the most complete and current information.
The left column lists Cisco software releases, and the right column
indicates whether a release was affected by the vulnerability described in
this advisory and which release included the fix for this vulnerability.
UCS 6200, 6300 and 6400 Series Fabric Interconnects
Cisco UCS Software Release First Fixed Release for This Vulnerability
Earlier than 4.0 Migrate to a fixed release.
4.0 4.0(4l)
4.1 4.1(2c)
4.2 Not vulnerable.
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 by Marco Cassini of Cisco 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: September 2021 Semiannual Cisco IOS and IOS XE
Software Security Advisory Bundled Publication
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-nxos-xr-udld-dos-W5hGHgtQ
Revision History
o +----------+---------------------------+----------+--------+--------------+
| Version | Description | Section | Status | Date |
+----------+---------------------------+----------+--------+--------------+
| 1.0 | Initial public release. | - | Final | 2021-SEP-22 |
+----------+---------------------------+----------+--------+--------------+
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