Cisco Security Advisory: Cisco CatOS Telnet, HTTP and SSH Vulnerability Jun 09 2004 04:27PM
Cisco Systems Product Security Incident Response Team (psirt cisco com)
Hash: SHA1

Cisco Security Advisory: Cisco CatOS Telnet, HTTP and SSH Vulnerability

Revision 1.0

For Public Release 2004 June 9 at 1600 UTC (GMT)



Affected Products
Software Versions and Fixes
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: FINAL
Revision History
Cisco Security Procedures



Cisco CatOS is susceptible to a TCP-ACK Denial of Service (DoS) attack on
the Telnet, HTTP and SSH service. If exploited, the vulnerability causes
the Cisco CatOS running device to stop functioning and reload.

This vulnerability is documented as Cisco bug IDs CSCec42751, CSCed45576,
and CSCed48590. There are techniques available to mitigate the potential
effects of this vulnerability in the workaround section of this advisory.
Cisco is providing fixed software, and recommends that customers upgrade
to it.

This advisory will be posted at

Affected Products

Vulnerable Products


* Catalyst 6000 series
* Catalyst 5000 series
* Catalyst 4500 series
* Catalyst 4000 series
* Catalyst 2948G, 2980G, 2980G-A, 4912G - use Catalyst 4000 series code
* Catalyst 2901, 2902, 2926[T,F,GS,GL], 2948 - use Catalyst 5000 series
code base


|CatOS Release Train| Affected Releases |
|8.xGLX |earlier than 8.3(2)GLX|
|8.x |earlier than 8.2(2) |
|7.x |earlier than 7.6(6) |
|6.x |earlier than 6.4(9) |
|5.x and earlier |earlier than 5.5(20) |

Products Confirmed Not Vulnerable

The following Catalyst switches do not run Cisco CatOS.

* Catalyst 8500 series
* Catalyst 4800 series
* Catalyst 4200 series
* Catalyst 4840G
* Catalyst 4908G-l3
* Catalyst 4224 Access Gateway Switch
* Catalyst 3750
* Catalyst 3750 Metro
* Catalyst 3560
* Catalyst 3550
* Catalyst 3500 XL
* Catalyst 2948G-l3
* Catalyst 2970
* Catalyst 2955
* Catalyst 2950
* Catalyst 2950 LRE
* Catalyst 2940
* Catalyst 2900 XL
* Catalyst 2900 LRE XL
* Catalyst 2820
* Catalyst 1900

Cisco IOS is not vulnerable to this issue.

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

To determine your software revision, type show version at the command line
prompt of the network device.


A TCP-ACK DoS attack is conducted by not sending the regular final ACK
required for a 3-way TCP handshake to complete, and instead sending an
invalid response to move the connection to an invalid TCP state. This
attack can be initiated from a remote spoofed source.

This vulnerability is currently known to be exploitable only if you have
the Telnet, HTTP or SSH service configured on a device which is running
Cisco CatOS.

CatOS release 5.4 was the first CatOS release which incorporated the HTTP
feature. Software releases that contain a "cv" in the image filename
support the HTTP feature. The HTTP server is disabled by default. It is
typically enabled to allow web based management of the switch using
CiscoView. To disable the HTTP server on the switch type set ip http
server disable.

CatOS K9 (crypto) release 6.1 was the first CatOS release which
incorporated the SSH feature. The SSH server is disabled by default. To
verify if SSH has been configured on the switch type show crypto key. If
this shows you the RSA key then SSH has been configured and enabled on the
switch. To remove the crypto key type clear crypto key RSA and this will
disable the SSH server on the switch.

To check if the HTTP or SSH services are enabled one can also do the
following: For HTTP, try and connect to the default HTTP port, TCP 80,
using Telnet. telnet ip_address_of_device 80. If the session connects, the
service is enabled and accessible. Similarly, for SSH try and connect to
the SSH port, TCP 22.

The Internetworking Terms and Cisco Systems Acronyms online guides can be
found at http://www.cisco.com/univercd/cc/td/doc/cisintwk/.

This vulnerability is documented in the Cisco Bug Toolkit as Bug IDs
CSCec42751 (registered customers only) , CSCed45576 (registered customers
only) , and CSCed48590 (registered customers only) .


When exploited, the vulnerability causes the Cisco CatOS running device to
stop functioning and reload.

Software Versions and Fixes

| CatOS Release Train | Fixed Releases |
|8.xGLX |8.3(2)GLX and later |
|8.x |8.2(2) and later |
|7.x |7.6(6) and later |
|6.x |6.4(9) and later |
|5.x and earlier |5.5(20) *1* |

The procedure to upgrade to the fixed software version is described at
Some Catalyst platforms may also require a boot ROM upgrade in conjunction
with a software upgrade, please refer to the appropriate software release

*1* If a device running fixed Cisco CatOS 5.5(20) version of code is being
actively attacked for this vulnerability, network management access over
the Ethernet interface may not be possible during that period; console
access would still be possible. This is due to the software architectural
limitations in 5.x. Customers are recommended to upgrade to 6.4(9) or

Obtaining Fixed Software

Cisco is offering free software upgrades to address this vulnerability for
all affected customers.

Customers with Service Contracts

Customers with contracts should obtain upgraded software through their
regular update channels. For most customers, this means that the software
upgrades should be obtained through the Software Center on Cisco's
worldwide website at http://www.cisco.com/tacpage/sw-center/sw-lan.shtml.

Customers using Third-party Support Organizations

Customers whose Cisco products are provided or maintained through prior or
existing agreement with third-party support organizations such as Cisco
Partners, authorized resellers, or service providers should contact that
support organization for assistance with the upgrade, which should be free
of charge.

Customers without Service Contracts

Customers who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third-party vendors
but are unsuccessful at obtaining fixed software through their point of
sale should get their upgrades by contacting the Cisco Technical
Assistance Center (TAC). TAC contacts are as follows.

* +1 800 553 2447 (toll free from within North America)
* +1 408 526 7209 (toll call from anywhere in the world)
* e-mail: tac (at) cisco (dot) com [email concealed]

Please have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free software upgrade. Free
upgrades for non-contract customers must be requested through the TAC.

Please do not contact either "psirt (at) cisco (dot) com [email concealed]" or
"security-alert (at) cisco (dot) com [email concealed]" for software upgrades.

See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for
additional TAC contact information, including special localized telephone
numbers and instructions and e-mail addresses for use in various

Customers may only install and expect support for the feature sets they
have purchased. By installing, downloading, accessing or otherwise using
such software upgrades, customers agree to be bound by the terms of
Cisco's software license terms found at
http://www.cisco.com/public/sw-license-agreement.html, or as otherwise set
forth at Cisco.com Downloads at


Implement the best practice of assigning all switch management interfaces
to a dedicated VLAN and apply appropriate access controls on routers
switching between the switch management interface VLAN and the rest of the
network. To read more about best practices for Catalyst 4500/4000,
5500/5000, and 6500/6000 Series Switches running CatOS configuration and
management, refer to

Apply ACLs on routers / switches / firewalls in front of the vulnerable
switches such that traffic destined for the Telnet TCP port 23, HTTP TCP
port 80 and SSH TCP port 22 on the vulnerable switches is only allowed
from the network management workstations. Refer to
http://www.cisco.com/warp/public/707/iacl.html for examples on how to
apply access control lists (ACLs) on Cisco routers.

On the Catalyst 6000 series switches, if the VLAN Access Control List
(VACL) feature is available in the code base, you can use VACLs to enable
Telnet, HTTP and SSH access to the switch's management interface only from
the network management workstations, refer to

Please note, these workarounds will not prevent spoofed IP packets with
the source IP address set to that of the network management station from
reaching the switch's management interface. For more information on
anti-spoofing refer to http://www.cisco.com/warp/public/707/21.html#sec_ip
and http://www.ietf.org/rfc/rfc2827.txt. The Unicast Reverse Path
Forwarding (Unicast RPF) feature helps to mitigate problems that are
caused by malformed or forged IP source addresses that are passing through
a router, refer to

IP Permit Lists will not provide any mitigation against this

The Cisco PSIRT recommends that affected users upgrade to a fixed software
version of code.

Exploitation and Public Announcements

The Cisco PSIRT is not aware of any public announcements or malicious use
of the vulnerability described in this advisory.

This vulnerability was found internally during testing.

Status of This Notice: FINAL

This Advisory is provided on an "as is" basis and does not imply any kind
of guarantee or warranty of any kind. Your use of the information on the
Advisory or materials linked from the Advisory is at your own risk. Cisco
reserves the right to change or update this notice at anytime.

A stand-alone copy or paraphrase of the text of this security advisory
that omits the distribution URL in the following section is an
uncontrolled copy, and may lack important information or contain factual


This advisory will be posted on Cisco's worldwide website at
http://www.cisco.com/warp/public/707/cisco-sa-20040609-catos.shtml .

In addition to worldwide web posting, a text version of this notice is
clear-signed with the Cisco PSIRT PGP key having the fingerprint 8C82 5207
0CA9 ED40 1DD2 EE2A 7B31 A8CF 32B6 B590 and is posted to the following
e-mail and Usenet news recipients.

* cust-security-announce (at) cisco (dot) com [email concealed]
* first-teams (at) first (dot) org [email concealed] (includes CERT/CC)
* bugtraq (at) securityfocus (dot) com [email concealed]
* vulnwatch (at) wulnwatch (dot) org [email concealed]
* cisco (at) spot.colorado (dot) edu [email concealed]
* cisco-nsp (at) puck.nether (dot) net [email concealed]
* full-disclosure (at) lists.netsys (dot) com [email concealed]
* comp.dcom.sys.cisco (at) newsgate.cisco (dot) com [email concealed]
* Various internal Cisco mailing lists

Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on mailing
lists or newsgroups. Users concerned about this problem are encouraged to
check the above URL for any updates.

Revision History

|Revision 1.0|2004-Jun-9|Initial public |
| | |release. |

Cisco Security Procedures

Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and registering to
receive security information from Cisco, is available on Cisco's worldwide
website at
http://www.cisco.com/warp/public/707/sec_incident_response.shtml. This
includes instructions for press inquiries regarding Cisco security
notices. All Cisco security advisories are available at


All contents are Copyright (c) 1992-2004 Cisco Systems, Inc. All rights
reserved. Important Notices and Privacy Statement.

Comment: Sharad Ahlawat, sha (at) cisco (dot) com [email concealed], Cisco Systems PSIRT


[ reply ]


Privacy Statement
Copyright 2010, SecurityFocus