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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
CVE Names: CVE-2019-12652
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Cisco Catalyst 4000 Series Switches TCP Denial of Service Vulnerability
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
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
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 .
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
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
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
| Version | Description | Section | Status | Date |
| 1.0 | Initial public | - | Final | 2019-September-25 |
| | release. | | | |
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