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             AUSCERT External Security Bulletin Redistribution

 Cisco IOS XE Software Web User Interface Denial of Service Vulnerability
                               23 March 2017


        AusCERT Security Bulletin Summary

Product:           Cisco IOS XE
Publisher:         Cisco Systems
Operating System:  Cisco
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2017-3856  

Original Bulletin: 

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Cisco IOS XE Software Web User Interface Denial of Service Vulnerability


Advisory ID:     cisco-sa-20170322-webui
First Published: 2017 March 22 16:00 GMT
Version 1.0:     Final
Workarounds:     No workarounds available
Cisco Bug IDs:
CVSS Score:
Base 8.6, Temporal 8.6


A vulnerability in the web user interface of Cisco IOS XE Software could allow
an unauthenticated, remote attacker to cause an affected device to reload.

The vulnerability is due to insufficient resource handling by the affected 
software when the web user interface is under a high load. An attacker could 
exploit this vulnerability by sending a high number of requests to the web 
user interface of the affected software. A successful exploit could allow the
attacker to cause the affected device to reload, resulting in a denial of 
service (DoS) condition.

To exploit this vulnerability, the attacker must have access to the management
interface of the affected software, which is typically connected to a 
restricted management network.

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 

Affected Products

Cisco IOS XE Software provides a web user interface that allows users to 
manage and monitor most aspects of a device by using an easy-to-read graphical
interface. To access a device by using the interface, the interface must be 
enabled for the device and a persistent web user interface transport map must
be configured and applied to the device. The transport map defines how the 
device handles incoming requests for the web user interface.

Vulnerable Products

This vulnerability affects Cisco devices that are running a vulnerable release
of Cisco IOS XE Software, if the web user interface of the software is 
enabled. By default, the web user interface is not enabled.

For information about which Cisco IOS XE Software releases are vulnerable, see
the Fixed Software section of this advisory.

Assessing the Web User Interface Configuration

To determine whether the web user interface is enabled and configured for a 
device, administrators can log in to the device and use the CLI to check for 
the presence of the following commands...

 transport-map type persistent webui transport-map-name

 transport type persistent webui input transport-map-name

...in addition to the ip http server or ip http secure-server global 
configuration command.

If those commands are present and configured, the web user interface is 
enabled and configured for the device. To determine whether those commands are
present and configured, administrators can use the show running-config | 
include http|transport command in the CLI.

The following example shows the output of the show running-config | include 
http|transport command for a router that is enabled and configured to use the
web user interface:

 Router# show running-config | include http|transport
 transport-map type persistent webui https-webui
 transport-map type persistent webui http-webui
 no ip http server
 ip http authentication local
 ip http secure-server
 transport type persistent webui input http-webui

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.


There are no workarounds that address this vulnerability. However, 
administrators can mitigate this vulnerability by disabling the web user 
interface for an affected device until the device is upgraded to a software 
release that addresses 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: 

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 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:

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.


This vulnerability was found during the resolution of a support case.



Revision History

Version Description 		Section 	Status 	Date 
1.0 	Initial public release. 		Final 	2017-March-22

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