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AUSCERT External Security Bulletin Redistribution
ESB-2021.2874
Cisco Nexus 9500 Series Switches Access Control List Bypass Vulnerability
26 August 2021
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AusCERT Security Bulletin Summary
---------------------------------
Product: Nexus 9500 Series Switches
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Unauthorised Access -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2021-1591
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nexus-acl-vrvQYPVe
- --------------------------BEGIN INCLUDED TEXT--------------------
Cisco Nexus 9500 Series Switches Access Control List Bypass Vulnerability
Priority: Medium
Advisory ID: cisco-sa-nexus-acl-vrvQYPVe
First Published: 2021 August 25 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCvx65385
CVE Names: CVE-2021-1591
CWEs: CWE-284
Summary
o A vulnerability in the EtherChannel port subscription logic of Cisco Nexus
9500 Series Switches could allow an unauthenticated, remote attacker to
bypass access control list (ACL) rules that are configured on an affected
device.
This vulnerability is due to oversubscription of resources that occurs when
applying ACLs to port channel interfaces. An attacker could exploit this
vulnerability by attempting to access network resources that are protected
by the ACL. A successful exploit could allow the attacker to access network
resources that would be protected by the ACL that was applied on the port
channel interface.
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-nexus-acl-vrvQYPVe
This advisory is part of the August 2021 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: August 2021 Cisco
FXOS and NX-OS Software Security Advisory Bundled Publication .
Affected Products
o Vulnerable Products
At the time of publication, this vulnerability affected Cisco Nexus 9500
Series Switches if they were running a vulnerable release of Cisco NX-OS
Software and had port channels configured with ACLs enabled. This
vulnerability is more likely to be exploited in port channels that have
member interfaces configured with subinterfaces.
For information about which Cisco software releases are vulnerable, see the
Fixed Software 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
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
Nexus 9000 Series Switches in standalone NX-OS mode, other than the
models referenced in Vulnerable Products
UCS 6200 Series Fabric Interconnects
UCS 6300 Series Fabric Interconnects
UCS 6400 Series Fabric Interconnects
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 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.
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 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: August 2021 Semiannual Cisco FXOS and NX-OS Software
Security Advisory Bundled Publication
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nexus-acl-vrvQYPVe
Revision History
o +----------+---------------------------+----------+--------+--------------+
| Version | Description | Section | Status | Date |
+----------+---------------------------+----------+--------+--------------+
| 1.0 | Initial public release. | - | Final | 2021-AUG-25 |
+----------+---------------------------+----------+--------+--------------+
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