Summary

• A vulnerability in the ingress packet processing function of Cisco IOS Software for Cisco Catalyst 4000 Series Switches could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.

  The vulnerability is due to improper resource allocation when processing TCP packets directed to the device on specific Cisco Catalyst 4000 Series Switches. An attacker could exploit this vulnerability by sending crafted TCP streams to an affected device. A successful exploit could cause the affected device to run out of buffer resources, impairing operations of control plane and management plane protocols, resulting in a DoS condition.

  This vulnerability can be triggered only by traffic that is 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.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190925-cat4000-tcp-dos

  This advisory is part of the September 25, 2019, release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication, which includes 12 Cisco Security Advisories that describe 13 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: September 2019 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco devices if they are running a vulnerable release of Cisco IOS Software:

  • Cisco Catalyst 4500 Supervisor Engine 6-E
  • Cisco Catalyst 4500 Supervisor Engine 6L-E
  • Cisco Catalyst 4900M Switch
  • Cisco Catalyst 4948E Ethernet Switch
  • Cisco Catalyst 4948E-F Ethernet Switch

  For information about which Cisco IOS Software releases were vulnerable at the time of publication, see the Fixed Software section of this advisory.

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

  Cisco has confirmed that this vulnerability does not affect Cisco IOS XE Software, Cisco IOS XR Software, or Cisco NX-OS Software.

Details

• Exploitation of this vulnerability may lead to exhaustion of buffer resources on an affected device, which in turn may prevent the device from accepting and processing unicast IP packets destined for the device. This may cause management protocols and control plane protocols relying on unicast IP traffic, including the BGP routing protocol, to stop working properly on the affected device, resulting in a DoS condition.

  This vulnerability can be exploited using crafted TCP streams over either IPv4 or IPv6. This vulnerability can be triggered only by TCP traffic that is destined to an affected device and cannot be exploited using traffic that transits an affected device.

  To exploit this vulnerability, an attacker must establish TCP connections to an open TCP port on the affected device. As a consequence, an attack cannot be performed using spoofed IP addresses.

Workarounds

• There are no workarounds that address this vulnerability.

  Use of infrastructure access control lists (iACLs) and vty ACLs as recommended in the Cisco Guide to Harden Cisco IOS Devices can help reduce the attack surface by allowing access only from explicitly trusted source IP addresses.

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:
  https://www.cisco.com/c/en/us/products/end-user-license-agreement.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 TAC:
  https://www.cisco.com/c/en/us/support/web/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 Software

  To help customers determine their exposure to vulnerabilities in Cisco IOS Software, Cisco provides a tool, the Cisco IOS Software Checker, that identifies any Cisco Security Advisories that impact a specific Cisco IOS 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 list 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 release—for example, 15.1(4)M2—in the following field:

  By default, the Cisco IOS Software Checker includes results only for vulnerabilities that have a Critical or High Security Impact Rating (SIR). To include results for Medium SIR vulnerabilities, use the Cisco IOS Software Checker on Cisco.com and check the Medium check box in the Impact Rating drop-down list.

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

• Cisco would like to thank Tim April, Trevers Astheimer, Aaron Block, John-Nicholas Furst, and Eric Kloster of Akamai for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190925-cat4000-tcp-dos

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2019-September-25

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