Summary

• 4A vulnerability in the TCP stack of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.
  
  The vulnerability is due to improper processing of certain TCP packets in the closing sequence of a TCP session while the affected device is in a TIME_WAIT state. An attacker could exploit this vulnerability by sending a specific TCP packet to an affected device on a TCP session that is already in a TIME_WAIT state. An exploit could allow the attacker to cause a reload of the TCP stack on the affected device, resulting in a DoS condition.
  
  This vulnerability can be exploited using either IPv4 or IPv6 packets. The vulnerability can be triggered by a crafted sequence of TCP packets destined for TCP ports listening on the device. The packets may use the IPv4 or IPv6 unicast address of any interface configured on the device.
  
  This vulnerability can be triggered only by traffic destined to an affected device and cannot be exploited using traffic that transits an affected device.
  
  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.comsecurity/center/content/CiscoSecurityAdvisory/cisco-sa-20160302-netstack

Affected Products

• 
  

  Vulnerable Products

  This vulnerability affects the following products:
  

  • Cisco Nexus 1000V Series Switches
  • Cisco Nexus 3000 Series Switches
  • Cisco Nexus 4000 Series Switches
  • Cisco Nexus 5000 Series Switches
  • Cisco Nexus 6000 Series Switches
  • Cisco Nexus 7000 Series Switches
  • Cisco Unified Computing System (UCS) running Cisco NX-OS Software

  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 command-line interface (CLI).
  
  The following example shows the output of this command for a Cisco Nexus 5000 Series Switch running Cisco NX-OS Software Release 7.1(1)N1(1):
  

  # 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) 2002-2012, Cisco Systems, Inc. All rights reserved.
  The copyrights to certain works contained herein are owned by
  other third parties and are used and distributed under license.
  Some parts of this software are covered under the GNU Public
  License. A copy of the license is available at
  http://www.gnu.org/licenses/gpl.html.
  
  Software
  BIOS:      version 3.6.0
  loader:    version N/A
  kickstart: version 7.1(1)N1(1)
  system:    version 7.1(1)N1(1)

  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 Multilayer Director Switches.

Indicators of Compromise

• Exploitation of this vulnerability will cause an affected device to reload and generate a netstack core file. Contact the Cisco Technical Assistance Center (TAC) to review the core file and determine whether the device has been compromised by exploitation of this vulnerability.

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 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-20160302-n5ksnmp: Cisco NX-OS Software SNMP Packet Denial of Service Vulnerability
  • cisco-sa-20160302-netstack: Cisco NX-OS Software TCP Netstack Denial of Service Vulnerability
  • cisco-sa-20160302-n3k: Cisco Nexus 3000 Series and 3500 Platform Switches Insecure Default Credentials 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 - Cisco UCS	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  Prior to 2.1	Affected; migrate to 2.2(2c)	2.2(2c) or later
  2.1	Affected; migrate to 2.2(2c)	2.2(2c) or later
  2.2	2.2(2c)	2.2(2c) or later
  3.0	Not affected	Not affected

  
  

  Cisco NX-OS Software Major Release - Nexus 1000V 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 5.2(1)SV3(1.1)	5.2(1)SV3(1.1) or later
  5.2	5.2(1)SV3(1.1)	5.2(1)SV3(1.1) or later

  
  

  Cisco NX-OS Software Major Release - Nexus 3000 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 6.0	Affected; migrate to 6.0(2)U1(1)	6.0(2)U6(5a) or later
  6.0	6.0(2)U1(1)	6.0(2)U6(5a) or later
  7.0	Not affected	Not affected

  
  

  Cisco NX-OS Software Major Release - Nexus 3500 Platform Switches	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  Prior to 6.0	Affected; migrate to 6.0(2)A1(1)	6.0(2)A6(5a) or later
  6.0	6.0(2)A1(1)	6.0(2)A6(5a) or later
  7.0	Not affected	Not affected

  
  

  Cisco NX-OS Software Major Release - Nexus 4000 Series Switches	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Collection of Advisories
  4.1	4.1(2)E1(1n)	4.1(2)E1(1n) or later

  
  

  Cisco NX-OS Software Major Release - Nexus 5000 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 5.2(1)N1(9)	5.2(1)N1(9) or later
  5.2	5.2(1)N1(9)	5.2(1)N1(9)or later

  
  

  Cisco NX-OS Software Major Release - Nexus 5500 Platform and 6000 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 5.2(1)N1(9)	7.1(2)N1(1) or later
  5.2	5.2(1)N1(9)	5.2(1)N1(9) or later
  6.0	6.0(2)N2(7)	6.0(2)N2(7) or later
  7.0	7.0(0)N1(1)	7.0(0)N1(1) or later
  7.1	Not affected	7.1(2)N1(1) or later
  7.2	Not affected	7.1(2)N1(1) or later

  
  

  Cisco NX-OS Software Major Release - Nexus 7000 Series 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 5.2(9)	5.2(9) or later
  5.2	5.2(9)	5.2(9) or later
  6.0	Affected; migrate to 6.1(4a)	6.1(4a) or later
  6.1	6.1(4a)	6.1(4a) or later
  6.2	6.2(2)	6.2(2) or later
  7.2	Not affected	Not affected
  7.3	Not affected	Not affected

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

  • Cisco Nexus 1000V for VMware Switches
  • Cisco Nexus 3000 Series and 3500 Series Switches
  • Cisco Nexus 5000 Series Switches
  • Cisco Nexus 5500 Platform Switches
  • Cisco Nexus 6000 Series Switches
  • Cisco Nexus 7000 Series Switches

  To determine the best NX-OS software release for Cisco UCS or a Cisco Nexus 4000 Series Switch, refer to the Recommended Releases documents in the release notes for the device.

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.comsecurity/center/content/CiscoSecurityAdvisory/cisco-sa-20160302-netstack

Revision History

• Version	Description	Section	Status	Date
  1.4	Metadata update.	—	Final	2017-December-05
  1.3	Metadata update.	—	Final	2017-November-28
  1.2	Metadata update.	—	Final	2017-October-20
  1.1	Updated the first fixed release for Nexus 3000 Series Switches.	Fixed Software	Final	2016-March-03
  1.0	Initial public release.	—	Final	2016-March-02

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