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AUSCERT External Security Bulletin Redistribution
Cisco IOS XR Software Border Gateway Protocol Attribute
Denial of Service Vulnerability
24 January 2020
AusCERT Security Bulletin Summary
Product: Cisco IOS XR
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2019-15989
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Cisco IOS XR Software Border Gateway Protocol Attribute Denial of Service
Advisory ID: cisco-sa-20200122-ios-xr-bgp-dos
First Published: 2020 January 22 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds availableCisco Bug IDs: CSCvr69950
o A vulnerability in the implementation of the Border Gateway Protocol (BGP)
functionality in Cisco IOS XR Software could allow an unauthenticated,
remote attacker to cause a denial of service (DoS) condition.
The vulnerability is due to incorrect processing of a BGP update message
that contains a specific BGP attribute. An attacker could exploit this
vulnerability by sending BGP update messages that include a specific,
malformed attribute 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 this vulnerability, 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 this vulnerability. There
are no workarounds that address this vulnerability.
This advisory is available at the following link:
o Vulnerable Products
At the time of publication, this vulnerability affected Cisco devices if
they running a vulnerable release of Cisco IOS XR Software and are
configured for BGP.
Cisco has confirmed that this vulnerability affects both Cisco IOS XR
32-bit Software and Cisco IOS XR 64-bit Software.
For information about which Cisco IOS XR Software releases were vulnerable
at the time of publication, see the Fixed Software section of this
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
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 Cisco IOS
Software, Cisco IOS XE Software, or Cisco NX-OS Software.
o The specific, malformed BGP update attribute that can allow this
vulnerability to be exploited is a non-transitive attribute. This means
that this vulnerability affects only Interior BGP (iBGP). The bad attribute
would be dropped at Autonomous System (AS) boundaries and could not be
transmitted through Exterior BGP (eBGP).
o There are no workarounds that address this vulnerability.
o 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
At the time of publication, Cisco planned to fix this vulnerability in
Cisco IOS XR Software releases 7.0.2, 7.1.1, and 7.2.1.
At the 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 XRV9K xrv9k-6.6.2.CSCvr91676
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
1. Fixes for the vulnerability described in this advisory were provided in
the fix 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.
For information about fixed software releases, see the Details section in
the bug ID(s) at the top of this advisory.
To download the SMUs from the Software Center on Cisco.com , do the
1. Click Browse All .
2. Choose IOS and NX-OS Software > IOS XR > IOS XR Software > Optical
Networking or Routers .
3. Choose the appropriate product and model from the right pane of the
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 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.
| Version | Description | Section | Status | Date |
| 1.0 | Initial public release. | - | Final | 2020-January-22 |
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