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AUSCERT External Security Bulletin Redistribution
Cisco IOS XE Software for Cisco ASR 920 Series Routers Zero
Touch Provisioning Denial of Service Vulnerability
23 March 2017
AusCERT Security Bulletin Summary
Product: Cisco ASR 920 Series Aggregation Services Routers
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2017-3859
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Cisco IOS XE Software for Cisco ASR 920 Series Routers Zero Touch Provisioning
Denial of Service Vulnerability
Advisory ID: cisco-sa-20170322-ztp
First Published: 2017 March 22 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs:
Base 8.6, Temporal 8.6
A vulnerability in the DHCP code for the Zero Touch Provisioning feature of
Cisco ASR 920 Series Aggregation Services Routers could allow an
unauthenticated, remote attacker to cause an affected device to reload.
The vulnerability is due to a format string vulnerability when processing a
crafted DHCP packet for Zero Touch Provisioning. An attacker could exploit
this vulnerability by sending a specially crafted DHCP packet to an affected
device. An exploit could allow the attacker to cause the device to reload,
resulting in a denial of service (DoS) condition.
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:
This advisory is part of the March 22, 2017, release of the Cisco IOS and IOS
XE Software Security Advisory Bundled Publication, which includes five Cisco
Security Advisories that describe five vulnerabilities. All the
vulnerabilities have a Security Impact Rating of High. For a complete list of
the advisories and links to them, see Cisco Event Response: March 2017
Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled
This vulnerability affects Cisco ASR 920 Series Aggregation Services Routers
that are running an affected release of Cisco IOS XE Software and are
listening on the DHCP server port. By default, the devices do not listen on
the DHCP server port.
For information about which Cisco IOS XE Software releases are vulnerable, see
the Fixed Software section of this advisory.
To determine whether a device is listening on the DHCP server port, use the
show ip sockets privileged EXEC command on the device. The following example
shows the output of the show ip sockets command on a Cisco IOS XE device
configured as a DHCP server and/or a DHCP relay agent. The Port 67 output
confirms that the device is listening for DHCP server packets:
ASR920# show ip sockets
Proto Remote Port Local Port In Out Stat TTY OutputIF
17 0.0.0.0 0 192.168.0.1 18999 0 0 11 0
17 0.0.0.0 0 --any-- 67 0 0 22211 0
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 XE
Software or similar text.
The following example shows the output of the show version command on a device
that is running Cisco IOS XE Software Release 3.16.1aS:
Router> show version
Cisco IOS XE Software, Version 03.16.01a.S - Extended Support
Release Cisco IOS Software, ASR1000 Software (PPC_LINUX_IOSD-
ADVENTERPRISEK9-M), Version 15.5(3)S1a, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2015 by Cisco Systems, Inc.
Compiled Wed 04-Nov-15 17:40 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
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
Software, Cisco IOS XR Software, or Cisco NX-OS Software.
Indicators of Compromise
Exploitation of this vulnerability will cause an affected device to reload and
generate a crashinfo file. Contact the Cisco Technical Assistance Center (TAC)
to review the file and determine whether the device has been compromised by
exploitation of this vulnerability. The device may crash with the following
UNIX-EXT-SIGNAL: Segmentation fault(11), Process = DHCPD Receive
There are no workarounds that address this vulnerability.
Cisco has released free software updates that address the vulnerability
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:
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
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:
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.
Cisco IOS and IOS XE Software
To help customers determine their exposure to vulnerabilities in Cisco IOS and
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
Software or Cisco IOS XE Software releasefor example, 15.1(4)M2 or 3.1.4Sin
the following field:
For a mapping of Cisco IOS XE Software releases to Cisco IOS Software
releases, refer to the Cisco IOS XE 2 Release Notes, Cisco IOS XE 3S Release
Notes, or Cisco IOS XE 3SG Release Notes, depending on the Cisco IOS XE
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 found during the resolution of a support case.
Version Description Section Status Date
1.0 Initial public release. Final 2017-March-22
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