Summary

• A vulnerability in the implementation of Network Address Translation (NAT) functionality in Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload.
  
  The vulnerability is due to improper handling of malformed ICMP packets by the affected software. An attacker could exploit this vulnerability by sending crafted ICMP packets that require NAT processing by an affected device. A successful 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:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160928-esp-nat
  
  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

• Vulnerable Products

  This vulnerability affects Cisco devices that are running a vulnerable release of Cisco IOS XE Software and have NAT configured on one or more device interfaces.

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

  Assessing the NAT Configuration

  To determine whether NAT is configured on one or more interfaces, administrators can log in to the device and do either of the following in the command-line interface (CLI):

  • Issue the show running-config | include ip nat|^interface command and check the output for the presence of ip nat outside or ip nat inside interface configurations
  • Issue the show ip nat statistics command and check the output for interfaces that have NAT configured

  The following example shows the output of the show running-config | include ip nat|^interface command on a router that has NAT configured on the Tunnel0, GigabitEthernet0/0/1, and GigabitEthernet0/0/2 interfaces:
  

  Router#show running-config | include ip nat|^interface
  interface Loopback0
  interface Tunnel0
   ip nat outside
  interface GigabitEthernet0/0/0
  interface GigabitEthernet0/0/1
   ip nat outside
  interface GigabitEthernet0/0/2
   ip nat inside
  interface GigabitEthernet0/0/3
  interface GigabitEthernet0/0/4
  interface GigabitEthernet0
  ip nat translation icmp-timeout 300
  .
  .
  .

  The following example shows the output of the show ip nat statistics command on the same router:

  Router#show ip nat statistics
  Total active translations: 0 (0 static, 0 dynamic; 0 extended)
  Outside interfaces:
    GigabitEthernet0/0/1, Tunnel0
  Inside interfaces:
    GigabitEthernet0/0/2
  Hits: 0  Misses: 0
  Expired translations: 0
  Dynamic mappings:
  -- Inside Source
  .
  .
  .

  
  

  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 Software, Cisco IOS XR Software, or Cisco NX-OS Software.

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 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-esp-nat

Revision History

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

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