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AUSCERT External Security Bulletin Redistribution
ESB-2020.0245.2
Cisco IOS XR Software BGP EVPN Denial of Service Vulnerabilities
10 February 2020
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco IOS XR
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2019-16023 CVE-2019-16022 CVE-2019-16021
CVE-2019-16020 CVE-2019-16019
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20200122-ios-xr-evpn
Revision History: February 10 2020: Advisory "cisco-sa-20200122-ios-xr-evpn"
revised to version 1.1; Included information on configurations that may
expose the vulnerabilities in the advisory
January 24 2020: Initial Release
- --------------------------BEGIN INCLUDED TEXT--------------------
Cisco IOS XR Software BGP EVPN Denial of Service Vulnerabilities
Priority: High
Advisory ID: cisco-sa-20200122-ios-xr-evpn
First Published: 2020 January 22 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCvr74413CSCvr74986CSCvr80793CSCvr83742CSCvr84254
CVE-2019-16019
CVE-2019-16020
CVE-2019-16021
CVE-2019-16022
CVE-2019-16023
CWE-399
CVSS Score:
8.6 AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
Summary
o Multiple vulnerabilities in the implementation of Border Gateway Protocol
(BGP) Ethernet VPN (EVPN) functionality in Cisco IOS XR Software could
allow an unauthenticated, remote attacker to cause a denial of service
(DoS) condition.
The vulnerabilities are due to incorrect processing of BGP update messages
that contain crafted EVPN attributes. An attacker could exploit these
vulnerabilities by sending BGP EVPN update messages with malformed
attributes to be processed by an affected system. A successful exploit
could allow the attacker to cause the BGP process to restart unexpectedly,
resulting in a DoS condition.
The Cisco implementation of BGP accepts incoming BGP traffic only from
explicitly defined peers. To exploit these vulnerabilities, the malicious
BGP update message would need to come from a configured, valid BGP peer, or
would need to be injected by the attacker into the victim's BGP network on
an existing, valid TCP connection to a BGP peer.
Cisco has released software updates that address these vulnerabilities.
There are no workarounds that address these vulnerabilities.
This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-20200122-ios-xr-evpn
Affected Products
o Vulnerable Products
These vulnerabilities affect Cisco devices if they are running a vulnerable
release of Cisco IOS XR Software later than 6.6.1 and are configured for
BGP on a device with the L2VPN EVPN address family.
Determine Whether the Device Has a Vulnerable Configuration
To determine whether the device is configured for BGP, administrators can
use the show running-config router bgp EXEC command in the CLI. If the
router is configured for BGP, this command will return output.
The following example shows the partial output of the show running-config
router bgp command on a device that is configured for BGP:
# show running-config router bgp
router bgp 65536
.
.
.
To determine whether the device is configured for the EVPN address family,
administrators can use the show running-config router bgp AS-Number
address-family l2vpn evpn EXEC command in the CLI . If the router is
configured for the BGP EVPN address family, this command will return
output.
The following example shows the partial output of the show running-config
router bgp AS-Number address-family l2vpn evpn command on a device with the
EVPN address family configured:
# show running-config router bgp 65536 address-family l2vpn evpn
router bgp 100
address-family l2vpn evpn
.
.
.
To determine whether the device has the EVPN configuration, administrators
can use the show running-config l2vpn and show running-config evpn EXEC
commands in the CLI. If the device is a provider edge router for EVPN, this
command will return output.
The following examples show the show running-config l2vpn and show
running-config evpn commands on a provider edge EVPN device:
# show running-config l2vpn
l2vpn
bridge group <bridge_group>
bridge-domain <bridge_domain>
.
.
.
interface <>
evi <evi>
!
!
!
.
.
.
# show running-config evpn
evpn
interface <interface>
ethernet-segment
identifier type <type and Ethernet Segment Identifier>
.
.
.
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory
are known to be affected by these vulnerabilities.
Cisco has confirmed that these vulnerabilities do not affect Cisco IOS
Software, Cisco IOS XE Software, or Cisco NX-OS Software.
Details
o Ethernet VPN (EVPN) is a next-generation solution that provides Ethernet
multipoint services over MPLS networks. Customers can learn more about EVPN
and configuration options in guides such as the L2VPN and Ethernet Services
Configuration Guide for Cisco ASR 9000 Series Routers and in guides for
other platforms that support this feature.
Workarounds
o There are no workarounds that address these vulnerabilities.
Fixed Software
o Cisco has released free software updates that address the vulnerabilities
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.
Fixed Releases
Cisco will fix these vulnerabilities in Cisco IOS XR Software Releases
6.6.3, 7.0.2, and 7.1.1.
At time of publication, the SMUs in the following table were available.
Customers who require SMUs for other platforms and releases are advised to
contact their support organization.
IOS XR Release Platform SMU Name ^1
6.6.1 NCS5500 ncs5500-6.6.1.CSCvr91660
6.6.1 ASR9K-X64 asr9k-x64-6.6.1.CSCvr91660
6.6.1 NCS540 ncs540-6.6.1.CSCvr91660
6.6.1 NCS6K ncs6k-6.6.1.CSCvr91660
6.6.2 ASR9K asr9k-px-6.6.2.CSCvr91676
6.6.2 ASR9K-X64 asr9k-x64-6.6.2.CSCvr91676
6.6.2 CRS
6.6.2 NCS5K
6.6.2 XRV9K xrv9k-6.6.2.CSCvr91676
6.6.25 NCS540
6.6.25 NCS540L
6.6.25 NCS560 ncs560-6.6.25.CSCvr91676
6.6.25 NCS5500 ncs5500-6.6.25.CSCvr91676
7.0.1 ASR9K-X64 asr9k-x64-7.0.1.CSCvr91676
7.0.1 NCS1K
7.0.1 NCS5K
7.0.1 NCS6K
7.0.1 NCS540
7.0.1 NCS540L
7.0.1 NCS560
7.0.1 NCS5500
7.0.1 XRV9K
1. Fixes for the vulnerabilities described in this advisory were provided
in the fixes for CSCvr91660 and CSCvr91676.
CSCvr91660 includes the fixes for CSCvr84254, CSCvr74986, CSCvr74413,
CSCvr80793, CSCvr83742, CSCvr74902, CSCvo90073, and CSCvr69950.
CSCvr91676 includes the fixes for CSCvr84254, CSCvr74986, CSCvr74413,
CSCvr80793, CSCvr83742, CSCvr74902, and CSCvr69950.
To download the software from the Software Center on Cisco.com do the
following:
1. Click Browse All .
2. Choose IOS and NX-OS Software > IOS XR > IOS XR Software > Optical
Networking or Routers .
3. Choose a specific product from the right pane of the product selector.
4. Choose a release from the left pane of the product page.
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 vulnerabilities that are
described in this advisory.
Source
o These vulnerabilities were found by Mrinmoy Ghosh 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.
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-20200122-ios-xr-evpn
Revision History
o +---------+------------------------+----------+--------+------------------+
| Version | Description | Section | Status | Date |
+---------+------------------------+----------+--------+------------------+
| | Included information | | | |
| | regarding additional | | | |
| 1.1 | configurations that | Affected | Final | 2020-February-07 |
| | may expose the | Products | | |
| | vulnerabilities in | | | |
| | this advisory. | | | |
+---------+------------------------+----------+--------+------------------+
| 1.0 | Initial public | - | Final | 2020-January-22 |
| | release. | | | |
+---------+------------------------+----------+--------+------------------+
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