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             AUSCERT External Security Bulletin Redistribution

  Cisco Catalyst 4000 Series Switches TCP Denial of Service Vulnerability
                             26 September 2019


        AusCERT Security Bulletin Summary

Product:           Catalyst 4000 switches
Publisher:         Cisco Systems
Operating System:  Cisco
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2019-12652  

Original Bulletin: 

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Cisco Catalyst 4000 Series Switches TCP Denial of Service Vulnerability

Priority:        High
Advisory ID:     cisco-sa-20190925-cat4000-tcp-dos
First Published: 2019 September 25 16:00 GMT
Version 1.0:     Final
Workarounds:     No workarounds available
Cisco Bug IDs:   CSCvk66730

CVSS Score:


  o 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:

    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

  o 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.


  o 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.


  o 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

  o 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:

    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

    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:

    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

    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:

    [                    ] [Check]

    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

  o 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.


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


  o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/

Revision History

  o +---------+------------------------+---------+--------+-------------------+
    | Version |      Description       | Section | Status |       Date        |
    | 1.0     | Initial public         | -       | Final  | 2019-September-25 |
    |         | release.               |         |        |                   |

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