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AUSCERT External Security Bulletin Redistribution
Cisco IOS XE Software Ethernet Virtual Private Network
Border Gateway Protocol Denial of Service Vulnerability
8 November 2017
AusCERT Security Bulletin Summary
Product: Cisco IOS XE Software
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2017-12319
Revision History: November 8 2017: Addition of Cisco bug identifier CSCui67191
November 6 2017: Initial Release
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Cisco Security Advisory
Cisco IOS XE Software Ethernet Virtual Private Network Border Gateway Protocol
Denial of Service Vulnerability
Advisory ID: cisco-sa-20171103-bgp
First Published: 2017 November 3 16:00 GMT
Version 1.1: Final
Workarounds: No workarounds available
Cisco Bug IDs:
Base 6.8 CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
A vulnerability in the Border Gateway Protocol (BGP) over an Ethernet Virtual
Private Network (EVPN) for Cisco IOS XE Software could allow an
unauthenticated, remote attacker to cause the device to reload, resulting in a
denial of service (DoS) condition, or potentially corrupt the BGP routing
table, which could result in network instability.
The vulnerability exists due to changes in the implementation of the BGP
MPLS-Based Ethernet VPN RFC (RFC 7432) draft between IOS XE software releases.
When the BGP Inclusive Multicast Ethernet Tag Route or BGP EVPN MAC/IP
Advertisement Route update packet is received, it could be possible that the
IP address length field is miscalculated. An attacker could exploit this
vulnerability by sending a crafted BGP packet to an affected device after the
BGP session was established. An exploit could allow the attacker to cause the
affected device to reload or corrupt the BGP routing table; either outcome
would result in a DoS.
The Cisco implementation of the BGP protocol only accepts incoming BGP traffic
from explicitly defined peers. To exploit this vulnerability, an attacker must
be able to send the malicious packets over a TCP connection that appears to
come from a trusted BGP peer, or inject malformed messages into the victim's
BGP network. This would require obtaining information about the BGP peers in
the affected system's trusted network.
The vulnerability may be triggered when the router receives a crafted BGP
message from a peer on an existing BGP session. At least one BGP neighbor
session must be established for a router to be vulnerable.
There are no workarounds that address this vulnerability.
This advisory is available at the following link:
This vulnerability affects all releases of Cisco IOS XE Software prior to
software release 16.3 that support BGP EVPN configurations. If the device is
not configured for EVPN, it is not vulnerable.
Determining the Cisco IOS XE Software Release
To determine which Cisco IOS XE Software release is running on a device,
administrators can log in to the device, use the show version command in the
CLI, and then refer to the system banner that appears. If the device is
running Cisco IOS XE Software, the system banner displays Cisco IOS Software,
Cisco IOS XE Software, or similar text.
The following example shows the output of the command for a device that is
running Cisco IOS XE Software Release 16.2.1 and has an installed image name
ios-xe-device# show version
Cisco IOS Software, Catalyst L3 Switch Software (CAT3K_CAA-UNIVERSALK9-M),
Version Denali 16.2.1, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2016 by Cisco Systems, Inc.
Compiled Sun 27-Mar-16 21:47 by mcpre
For information about the naming and numbering conventions for Cisco IOS XE
Software releases, see White Paper: Cisco IOS and NX-OS Software Reference
Guide. For additional information on EVPN configurations, see Carrier Ethernet
Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by this
Cisco has confirmed that this vulnerability does not affect Cisco IOS XR
Software and Cisco NX-OS Software.
There are no workarounds that address this vulnerability.
Cisco has released free software updates that address the vulnerability
described in this advisory. Cisco will continue to provide fixes for affected
releases as they become available.
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
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 IOS XE Software
This vulnerability is fixed in IOS XE software releases 16.3 and later.
To help customers determine their exposure to vulnerabilities in Cisco IOS XE
Software, Cisco provides a tool, the Cisco IOS Software Checker, that
identifies 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 this tool to perform the following tasks:
Initiate a search by choosing one or more releases from a drop-down menu or
uploading a file from a local system for the tool to parse
Enter the output of the show version command for the tool to parse
Create a custom search by including all previously published Cisco Security
Advisories, a specific advisory, or all advisories in the most recent bundled
To determine whether a release is affected by any published Cisco Security
Advisory, use the Cisco IOS Software Checker on Cisco.com or enter a Cisco IOS
XE Software releasefor example, 15.1(4)M2in the following field:
Exploitation and Public Announcements
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.
This vulnerability was reported to Cisco by a customer via a Cisco TAC case.
Version Description Section Status Date
1.1 Added a second Cisco Product Attribute Set Final 2017-November-07
bug identifier: CSCui67191.
1.0 Initial public release. Final 2017-November-03
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF
GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS
LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO
CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A standalone copy or paraphrase of the text of this document that omits the
distribution URL is an uncontrolled copy and may lack important information or
contain factual errors. The information in this document is intended for end
users of Cisco products.
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