-----BEGIN PGP SIGNED MESSAGE-----
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)

----------------------------------------------------------------------

Contents

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

----------------------------------------------------------------------

Summary

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
http://www.cisco.com/warp/public/707...9-catos.shtml.

Affected Products

Vulnerable Products

Hardware

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

Software

+------------------------------------------+
|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
vulnerability.

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

Details

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) .

Impact

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
http://www.cisco.com/univercd/cc/td/...gd/images.htm.
Some Catalyst platforms may also require a boot ROM upgrade in conjunction
with a software upgrade, please refer to the appropriate software release
notes.

*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
later.

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@cisco.com

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@cisco.com" or
"security-alert@cisco.com" for software upgrades.

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

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
http://www.cisco.com/public/sw-cente...singswc.shtml.

Workarounds

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
http://www.cisco.com/en/US/partner/p...0094713.shtml.

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
http://www.cisco.com/univercd/cc/td/.../acc_list.htm.

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
http://www.cisco.com/univercd/cc/td/...rsf/scfrpf.htm