Advisory ID: cisco-sa-20001213-catalyst-ssh-mismatch
For Public Release 2000 December 13 18:00 UTC (GMT)
Non-Secure Shell (SSH) connection attempts to an enabled SSH service on
a Cisco Catalyst 6000, 5000, or 4000 switch might cause a "protocol mismatch"
error, resulting in a supervisor engine failure. The supervisor engine failure
causes the switch to fail to pass traffic and reboots the switch. This problem
is resolved in release 6.1(1c). Due to a very limited number of customer
downloads, Cisco has chosen to notify affected customers directly.
This vulnerability has been assigned Cisco bug ID CSCds85763.
The full text of this advisory can be viewed at
This section supplies details on affected products.
Catalyst 6000, 5000, 4000 images with SSH support. Version 6.1(1),
6.1(1a), 6.1(1b) with 3 Data Encryption Standard (DES) features only.
Only the following images are affected:
Cisco IOS 12.1 SSH implementation is not affected by this
vulnerability. No other Cisco devices are affected.
Non SSH protocol connection attempts to the SSH service cause a
"protocol mismatch" error, which causes a switch to reload. SSH is not enabled
by default, and must be configured by the administrator.
To verify if your image is affected, run the command show
version. If the image filename is listed above, and you have
enabled SSH, you are affected by this vulnerability and should upgrade to a
fixed version immediately.
Cisco has provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS version 2.0.
CVSS is a standards-based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.
Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.
Cisco has provided an FAQ to answer additional questions regarding CVSS at
Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at
This vulnerability enables a Denial of Service attack on the Catalyst
This defect is resolved in Cisco Catalyst version 6.1(1c). Previous
affected versions will be deferred, and will no longer be available for
The workaround for this vulnerability is to disable SSH service. For
most customers using this image, SSH support is necessary, so the recommended
action is to upgrade to a fixed version.
Cisco is offering free software upgrades to remedy this vulnerability
for all affected customers.
Customers with contracts should obtain upgraded software through their
regular update channels. For most customers, this means that upgrades should be
obtained via the Software Center on Cisco's Worldwide Web site at
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 guidance and assistance with the appropriate course of
action in regards to this advisory.
The effectiveness of any workaround or fix is dependent on specific
customer situations such as product mix, network topology, traffic behavior,
and organizational mission. Due to the variety of affected products and
releases, customers should consult with their service provider or support
organization to ensure any applied workaround or fix is the most appropriate
for use in the intended network before it is deployed.
Customers without contracts 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)
of this notice as evidence of your entitlement to a free upgrade. Free upgrades
for non-contract customers must be requested through the TAC. Please do not
contact either "email@example.com" or "firstname.lastname@example.org" for software
This vulnerability was reported to Cisco by a customer who discovered
the issue during routine networking tests. There has been no public disclosure,
and no reports of malicious activity with regard to this vulnerability.
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.
This advisory will be posted on Cisco's worldwide website at
In addition to Worldwide Web posting, a text version of this notice is
clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail
Various internal Cisco mailing lists
Specifically affected customers
Future updates of this notice, if any, will be placed on Cisco's
Worldwide Web server, but may or may not be actively announced on mailing lists
or newsgroups. Users concerned about this problem are encouraged to check the
URL given above for any updates.
Updated list of affected products.
Updated list of affected products.
Initial public release.