Summary

• The Smart Install client feature in Cisco IOS and IOS XE Software contains a vulnerability that could allow an unauthenticated, remote attacker to cause a memory leak and eventual denial of service (DoS) condition on an affected device.
  
  The vulnerability is due to incorrect handling of image list parameters. An attacker could exploit this vulnerability by sending crafted Smart Install packets to TCP port 4786. A successful exploit could cause a Cisco Catalyst switch to leak memory and eventually reload, resulting in a DoS condition.
  
  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability other than disabling Smart Install functionality on the affected device.
  
  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160928-smi
  
  This advisory is part of the September 28, 2016, release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication, which includes 10 Cisco Security Advisories that describe 11 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: September 2016 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.
  

Affected Products

• The Smart Install client feature in Cisco IOS and IOS XE Software is a plug-and-play configuration and image-management feature that provides zero-touch deployment for new switches. The feature allows a customer to ship a Cisco switch to any location, install it in the network, and power it on without additional configuration requirements.

  Vulnerable Products

  This vulnerability affects Cisco devices that are running a vulnerable release of Cisco IOS Software or Cisco IOS XE Software with the Smart Install client feature enabled.
  
  For information about which Cisco IOS and IOS XE Software releases are vulnerable, see the Fixed Software section of this advisory.
  
  Smart Install client functionality is enabled by default on Cisco IOS switches. Cisco devices that are configured as a Smart Install director are not affected by this vulnerability. Switches running releases earlier than Cisco IOS Software Release 12.2(52)SE are not Smart Install capable, but they can be Smart Install clients if they support the archive download-sw privileged EXEC command.
  
  To determine whether a device is configured with the Smart Install client feature enabled, use the show vstack config privileged EXEC command on the Smart Install client. The following is the output of the show vstack config command in a Cisco Catalyst Switch configured as a Smart Install client. The output for Role: Client from the show vstack config command confirms that the feature is enabled on the device.
  

  switch#show vstack config  
   Role: Client  Vstack Director IP address: 10.1.1.100

  
  

  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 command-line interface (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 Software or Cisco NX-OS Software.

Indicators of Compromise

• Exploitation of this vulnerability will cause an affected device to leak memory and eventually reload.

Workarounds

• There are no workarounds that address this vulnerability other than disabling the Smart Install feature. The Smart Install Feature is enabled by default on client switches. No configuration is needed in the client switches.
  
  In certain releases of Cisco IOS and IOS XE Software, the Smart Install client feature can be disabled with the global configuration command no vstack. In certain releases of Cisco IOS and IOS XE Software where the command is available, the vulnerability can be addressed by disabling the Smart Install client feature.

  The following example shows the output of the show vstack config command in a Cisco Catalyst Switch with the Smart Install client feature disabled:

  switch#show vstack config  
   Role: Client (SmartInstall disabled)  
  Vstack Director IP address: 10.1.1.100
  

  Note: Use of the no vstack global configuration command to disable the Smart Install client feature was introduced with the fix for Cisco bug CSCtj75729 (Ability to shut Smart Install default service on TCP port 4786). If a Cisco IOS or IOS XE Software release supports the Smart Install client feature but the no vstack command does not exist, the release does not contain the fix for Cisco bug CSCtj75729.

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 Technical Assistance Center (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 release—for example, 15.1(4)M2 or 3.1.4S—in 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.

Source

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

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160928-smi

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2016-September-28

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