Summary

• A vulnerability in the Overlay Transport Virtualization (OTV) generic routing encapsulation (GRE) implementation of the Cisco Nexus 7000 and 7700 Series Switches could allow an unauthenticated, adjacent attacker to cause a reload of the affected system or to remotely execute code.
  
  The vulnerability is due to incomplete input validation performed on the size of OTV packet header parameters, which can result in a buffer overflow. An attacker could exploit this vulnerability by sending a crafted OTV UDP packet to the OTV interface on an affected device. An exploit could allow the attacker to execute arbitrary code and obtain full control of the system or cause a reload of the OTV related process on the affected device.
  
  Cisco has released software updates that address this vulnerability. A workaround to mitigate this vulnerability is available.
  
  This advisory is available at the following link:
  
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20161005-otv

Affected Products

• Vulnerable Products

  The following Cisco products are affected by this vulnerability when configured to use the OTV functionality:
  

  • Nexus 7000 Series Switches
  • Nexus 7700 Series Switches

  This vulnerability affects Cisco Nexus 7000 and 7700 Series Switches with the OTV feature enabled. The OTV feature was introduced with Cisco NX-OS Software Release 5.0(3) or later for the Nexus 7000 Series, and Cisco NX-OS Software Release 6.2(2) or later for the Nexus 7700 Series. 
  
  To determine whether a Nexus device is configured to use the OTV functionality, administrators can use the show running | include otv command from the NX-OS command-line interface (CLI) and verify that the feature is enabled. The following example shows the OTV feature enabled on Nexus 7700 Series Switch:
  

  nxos-switch# show running-config | include otv
  feature otv
    otv join-interface ...
  nxos-switch#

  To determine whether a device is running a vulnerable release of Cisco NX-OS Software, administrators can use the show version command in the NX-OS CLI. The following example shows the output of this command for a Nexus 7000 Series Switch running Cisco NX-OS Software Release 6.2(14):
  

  nxos-switch# show version
  Cisco Nexus Operating System (NX-OS) Software
  TAC support: http://www.cisco.com/tac
  Documents:
  http://www.cisco.com/en/US/products/ps9372/tsd_products_support_series_home.html
  Copyright (c) 2002-2015, Cisco Systems, Inc. All rights reserved.
  The copyrights to certain works contained in this software are
  owned by other third parties and used and distributed under
  license. Certain components of this software are licensed under
  the GNU General Public License (GPL) version 2.0 or the GNU
  Lesser General Public License (LGPL) Version 2.1. A copy of each
  such license is available at
  http://www.opensource.org/licenses/gpl-2.0.php and
  http://www.opensource.org/licenses/lgpl-2.1.php
  
  Software
    BIOS:      version 2.12.0
    kickstart: version 6.2(14)
    system:    version 6.2(14)
  .
  .
  .

  Products Confirmed Not Vulnerable

  Cisco has confirmed that this vulnerability does not affect the following Cisco products:
  

  • Multilayer Director Switches
  • Nexus 1000 Series Switches
  • Nexus 2000 Series Fabric Extenders
  • Nexus 3000 Series Switches
  • Nexus 3500 Series Switches
  • Nexus 4000 Series Switches
  • Nexus 5000 Series Switches 
  • Nexus 9000 Series Switches in NX-OS mode
  • Nexus 9000 Series Switches in ACI mode
  • Unified Computing System (UCS) 6100 Series Fabric Interconnects
  • Unified Computing System (UCS) 6200 Series Fabric Interconnects

  No other Cisco products are currently known to be affected by this vulnerability.
  

Indicators of Compromise

• Exploitation of this vulnerability could cause an affected device to reload and generate an Intermediate System-to-Intermediate System (ISIS) core file. To view the ISIS core file, administrators can use the show core command in the NX-OS CLI. Contact the Cisco Technical Assistance Center (TAC) to review the ISIS core file and determine whether the device has been compromised by exploitation of this vulnerability.

Workarounds

• The following Access Control List (ACL) can be configured to drop malformed OTV control packets.
  

  IP access list OTV_PROT_V1
    10 deny udp any any fragments 
    20 deny udp any any eq 8472 packet-length lt 54 
    30 permit ip any any

  Please note the following considerations when applying this ACL workaround:
  

  • The deny udp fragment must be the first line of the ACL.
  • In the example between sequences 10-20 and 20-30 other Access Control Entries (ACEs) can be added as long as they don't contradict sequence 10 or 20.
  • The ACL must be configured on the ingress ACL for the OTV join interface.
  • In the example instead of any as the destination address there can be multiple ACEs each with an OTV interface IP address.

  The command show system internal access-list interface <interface> input statistics can be used to verify the ACL status.

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 consult the Cisco Security Advisories and Responses archive at http://www.cisco.com/go/psirt and review subsequent advisories to determine exposure and a complete upgrade solution.
  
  In all cases, customers should ensure that the devices to upgrade 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.
  
  Fixed Releases
  
  Customers should upgrade to an appropriate release as indicated in the applicable table in this section. To help ensure a complete upgrade solution, consider that this advisory is part of a collection that includes the following advisories:
  
  cisco-sa-20161005-bgp: Cisco NX-OS Border Gateway Protocol Denial of Service Vulnerability
  cisco-sa-20161005-dhcp1: Cisco NX-OS Software Crafted DHCPv4 Packet Denial of Service Vulnerability
  cisco-sa-20161005-dhcp2: Cisco NX-OS Software Malformed DHCPv4 Packet Denial of Service Vulnerability
  cisco-sa-20161005-nxaaa: Cisco NX-OS Software-Based Products Authentication, Authorization, and Accounting Bypass Vulnerability
  cisco-sa-20161005-otv: Cisco Nexus 7000 and 7700 Series Switches Overlay Transport Virtualization Buffer Overflow Vulnerability
  
  In the following table, the left column lists major releases of Cisco NX-OS Software. The center column indicates whether a major release is affected by the vulnerability described in this advisory and the first minor release that includes the fix for this vulnerability. The right column indicates whether a major release is affected by all the vulnerabilities described in this collection of advisories and which release includes fixes for those vulnerabilities.
  
  

  Cisco NX-OS Software Major Release - Nexus 7000 and 7700 Series Switches	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  Prior to 5.2	Affected; migrate to 7.2(2)D1(1)	7.2(2)D1(1)
  5.2	Affected; migrate to 7.2(2)D1(1)	7.2(2)D1(1)
  6.0	Affected; migrate to 7.2(2)D1(1)	7.2(2)D1(1)
  6.1	Affected; migrate to 7.2(2)D1(1)	7.2(2)D1(1)
  6.2	Affected; migrate to  7.2(2)D1(1)	7.2(2)D1(1)
  7.2	7.2(2)D1(1)	7.2(2)D1(1)
  7.3	7.3(0)DX(1) 7.3(1)D1(1)	7.3(1)D1(1)

  
  Release Recommendations
  
  For additional assistance in determining the best Cisco NX-OS Software release for a Cisco Nexus Switch, refer to the recommended release document for the switch:
  

  • Cisco Nexus 7000 Series Switches

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-20161005-otv

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2016-October-05

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