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AUSCERT External Security Bulletin Redistribution
ESB-2017.0771
Cisco IOS and IOS XE Software DHCP Client Denial of Service Vulnerability
23 March 2017
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco IOS
Cisco IOS XE
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2017-3864
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170322-dhcpc
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Cisco IOS and IOS XE Software DHCP Client Denial of Service Vulnerability
High
Advisory ID: cisco-sa-20170322-dhcpc
First Published: 2017 March 22 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs:
CSCuu43892
CVSS Score:
Base 8.6, Temporal 8.6
CVE-2017-3864
CWE-399
Summary
A vulnerability in the DHCP client implementation of Cisco IOS and Cisco IOS
XE Software could allow an unauthenticated, remote attacker to cause a denial
of service (DoS) condition.
The vulnerability occurs during the parsing of a crafted DHCP packet. An
attacker could exploit this vulnerability by sending crafted DHCP packets to
an affected device that is configured as a DHCP client. A successful exploit
could allow the attacker to cause a reload of an affected device, resulting in
a 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:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170322-dhcpc
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
Publication.
Affected Products
Vulnerable Products
This vulnerability affects Cisco devices that are running a vulnerable release
of Cisco IOS or IOS XE Software and using a specific DHCP client
configuration.
For information about which Cisco IOS and IOS XE Software releases are
vulnerable, see the Fixed Software section of this advisory.
To determine whether a Cisco device running Cisco IOS or IOS XE Software is
affected, perform the following steps:
Confirm whether the device is configured as a DHCP client by using the
show running-config | include dhcp privileged EXEC command on the device.
The following is the output of the show running-config | include dhcp
command for a Cisco IOS device configured as a DHCP client. The ip address
dhcp output confirms that the feature is enabled on one of the interfaces:
Router# show running-config | include dhcp
ip address dhcp
If the device is not configured as a DHCP client, the device is not
vulnerable. If the device is configured as a DHCP client, proceed to the next
step.
Confirm whether the device is configured as a DHCP server or DHCP relay
agent by using the show running-config | include helper|(ip dhcp pool)
privileged EXEC command on the device.
The following is the output of the show running-config | include
helper|(ip dhcp pool) command for a Cisco IOS device configured as a DHCP
relay agent. The ip helper-address 192.168.0.1 output confirms that the
feature is enabled on one of the interfaces:
Router# show running-config | include helper|(ip dhcp pool)
ip helper-address 192.168.0.1
If the device is not configured as a DHCP server or DHCP relay agent, the
device is not vulnerable; otherwise, proceed to the next step.
Confirm whether the device is configured to send DHCP Inform and Discover
messages by using the show run | include (ip dhcp-client network-discovery)
privileged EXEC command on the device.
The following is the output of the show run | include (ip dhcp-client
network-discovery) command for a Cisco IOS device configured to send DHCP
Inform and Discover messages. The ip dhcp-client network-discovery informs 1
discovers 1 period 15 output confirms that the feature is enabled:
Router# show running-config | include (ip dhcp-client
network-discovery)
ip dhcp-client network-discovery informs 1 discovers 1 period 15
Router#
If the device is configured to send DHCP Inform and Discover messages, the
device is not vulnerable.
The following table depicts the preceding information in a tabular format:
Vulnerable State Configuration
DHCP Client DHCP Server/Relay DHCP Inform/Discover
Not Vulnerable *
Not Vulnerable *
Not Vulnerable *
Vulnerable * *
Not Vulnerable * *
Not Vulnerable * *
Not Vulnerable * * *
Determining the Cisco IOS Software Release
To determine which Cisco IOS 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 Software, the system banner displays text similar to Cisco
Internetwork Operating System Software or Cisco IOS Software. The banner also
displays the installed image name in parentheses, followed by the Cisco IOS
Software release number and release name. Some Cisco devices do not support
the show version command or may provide different output.
The following example identifies a Cisco product that is running Cisco IOS
Software Release 15.5(2)T1 with an installed image name of
C2951-UNIVERSALK9-M:
Router> show version
Cisco IOS Software, C2951 Software (C2951-UNIVERSALK9-M),
Version 15.5(2)T1, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2015 by Cisco Systems, Inc.
Compiled Mon 22-Jun-15 09:32 by prod_rel_team
.
.
.
For information about the naming and numbering conventions for Cisco IOS
Software releases, see White Paper: Cisco IOS and NX-OS Software Reference
Guide.
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
Guide.
Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by this
vulnerability.
Cisco has confirmed that this vulnerability does not affect Cisco IOS XR 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. A stack trace may point to Process = DHCPD
Receive.
Workarounds
There are no workarounds that address this vulnerability.
Fixed Software
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:
http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.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:
http://www.cisco.com/en/US/support/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.
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 publication
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:
Note: Cisco IOS XE Software trains were patched early via Cisco bug CSCsy76009
(registered customers only). Use the Cisco IOS Software Checker to obtain a
list of affected releases.
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
Software release.
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.
Source
This vulnerability was found during the resolution of a support case.
URL
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170322-dhcpc
Revision History
Version Description Section Status Date
1.0 Initial public release. Final 2017-March-22
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