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AUSCERT External Security Bulletin Redistribution
Cisco IOS XE Software IPv6 VPN over MPLS Denial of Service Vulnerability
29 September 2022
AusCERT Security Bulletin Summary
Product: Cisco IOS XE
Publisher: Cisco Systems
Operating System: Cisco
CVE Names: CVE-2022-20915
Comment: CVSS (Max): 7.4 CVE-2022-20915 (CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H)
CVSS Source: Cisco Systems
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Cisco IOS XE Software IPv6 VPN over MPLS Denial of Service Vulnerability
Advisory ID: cisco-sa-iosxe-6vpe-dos-tJBtf5Zv
First Published: 2022 September 28 16:00 GMT
Version 1.0: Final
Cisco Bug IDs: CSCwa41184
CVE Names: CVE-2022-20915
o A vulnerability in the implementation of IPv6 VPN over MPLS (6VPE) with
Zone-Based Firewall (ZBFW) of Cisco IOS XE Software could allow an
unauthenticated, adjacent attacker to cause a denial of service (DoS)
condition on an affected device.
This vulnerability is due to improper error handling of an IPv6 packet that
is forwarded from an MPLS and ZBFW-enabled interface in a 6VPE deployment.
An attacker could exploit this vulnerability by sending a crafted IPv6
packet sourced from a device on the IPv6-enabled virtual routing and
forwarding (VRF) interface through the affected device. A successful
exploit could allow the attacker to reload the device, resulting in a DoS
Cisco has released software updates that address this vulnerability. There
are workarounds that address this vulnerability.
This advisory is available at the following link:
This advisory is part of the September 2022 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
2022 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled
o Vulnerable Products
This vulnerability affects Cisco devices if they are running a vulnerable
release of Cisco IOS XE Software and have both 6VPE and ZBFW features
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory.
Determine the Device Configuration
Determine Whether IPv6 VPN Is Enabled
To determine whether IPv6 VPN is enabled, issue the show running-config |
include address-family vpnv6 CLI command. If there is an error or no
output, IPv6 VPN is not enabled. The following output shows a device with
IPv6 VPN enabled:
Router# show running-config | include address-family vpnv6
Determine Whether MPLS and ZBFW Are Enabled
To determine whether MPLS and ZBFW are enabled, issue the show
running-config | include interface|zone-member|mpls ip CLI command. The
following output shows an interface that has both MPLS and ZBFW enabled.
Router# show running-config | include interface|zone-member|mpls ip
zone-member security zone_name
If both mpls ip and zone-member security are displayed on the same
interface and address-family vpnv6 is configured, further verification is
required. Because 6VPE is the mechanism by which the IPv4 MPLS backbone
provides IPv6 VPN services, the IPv6 routing table must be investigated to
confirm whether IPv6 VPN networks are being forwarded though an IPv4 MPLS
backbone. For more information about 6VPE, see the MPLS Layer 3 VPNs
Configuration Guide .
Note : IPv6 over MPLS (6PE) configurations are not affected.
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
IOS XR Software
o There is a workaround that addresses this vulnerability. Administrators can
disable ICMPv6 unreachables on the mpls ip and zone-member security enabled
interface with the CLI command no ipv6 unreachables .
While this workaround has been deployed and was proven successful in a test
environment, customers should determine the applicability and effectiveness
in their own environment and under their own use conditions. Customers
should be aware that any workaround or mitigation that is implemented may
negatively impact the functionality or performance of their network based
on intrinsic customer deployment scenarios and limitations. Customers
should not deploy any workarounds or mitigations before first evaluating
the applicability to their own environment and any impact to such
o Cisco has released free software updates that address the vulnerability
described in this advisory. Customers with service contracts that entitle
them to regular software updates should obtain security fixes through their
usual update channels.
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:
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.
The Cisco Support and Downloads page on Cisco.com provides information
about licensing and downloads. This page can also display customer device
support coverage for customers who use the My Devices tool.
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
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
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
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
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 . This tool
identifies any Cisco security advisories that impact a specific 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 that are
described in all the advisories that the Software Checker identifies
("Combined First Fixed").
To use the tool, go to the Cisco Software Checker page and follow the
instructions. Alternatively, use the following form to determine whether a
release is affected by any Cisco Security Advisory. To use the form, follow
1. Choose which advisories the tool will search-only this advisory, only
advisories with a Critical or High Security Impact Rating (SIR) , or
2. Enter a release number-for example, 15.9(3)M2 or 17.3.3.
3. Click Check
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.
o This vulnerability was found during the resolution of a Cisco TAC support
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 2022 Semiannual Cisco IOS and IOS XE
Software Security Advisory Bundled Publication
| Version | Description | Section | Status | Date |
| 1.0 | Initial public release. | - | Final | 2022-SEP-28 |
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