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Cisco Security Advisory

Cisco CatOS Telnet Buffer Vulnerability

Advisory ID: cisco-sa-20020129-catos-telrcv

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20020129-catos-telrcv

Revision 1.2

For Public Release 2002 January 29 15:00  UTC (GMT)

Related Resources:

View related Security AdvisoryView related Alert

Summary

Some Cisco Catalyst switches, running certain CatOS based software releases, have a vulnerability wherein a buffer overflow in the Telnet option handling can cause the Telnet daemon to crash and result in a switch reload.

This vulnerability can be exploited to initiate a denial of service (DoS) attack. This vulnerability is documented as Cisco bug ID CSCdw19195. There are workarounds available to mitigate the vulnerability.

This advisory is available at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20020129-catos-telrcv.

Affected Products

This section provides details on affected products.

Vulnerable Products

The following Cisco Catalyst Switches are vulnerable:

  • Catalyst 6000 series
  • Catalyst 5000 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

For the switches above, the following CatOS-based switch software revisions are vulnerable.

Release 4 code base

Release 5 code base

Release 6 code base

Release 7 code base

Catalyst 6000 series

Not applicable

Earlier than 5.5(13)

Earlier than 6.3(4)

Earlier than 7.1(2)

Catalyst 5000 series

Earlier than 4.5(13a)

Earlier than 5.5(13)

Earlier than 6.3(4)

Not applicable

Catalyst 4000 series

All releases

Earlier than 5.5(13)

Earlier than 6.3(4)

Earlier than 7.1(2)

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

Products Confirmed Not Vulnerable

Cisco's various Catalyst family of switches run CatOS-based releases or IOS-based releases. IOS-based releases are not vulnerable.

The following Cisco Catalyst switches are not vulnerable:

  • Catalyst 8500 series
  • Catalyst 4800 series
  • Catalyst 4200 series
  • Catalyst 3900 series
  • Catalyst 3550 series
  • Catalyst 3500 XL series
  • Catalyst 4840G
  • Catalyst 4908G-l3
  • Catalyst 2948G-l3
  • Catalyst 2950
  • Catalyst 2900 XL
  • Catalyst 2900 LRE XL
  • Catalyst 2820
  • Catalyst 1900

No other Cisco products are currently known to be affected by these vulnerabilities.

Details

Some Cisco Catalyst switches, running certain CatOS-based software releases, have a vulnerability wherein a buffer overflow in the Telnet option handling can cause the Telnet daemon to crash and result in a switch reload. This vulnerability can be exploited to initiate a denial of service (DoS) attack. Once the switch has reloaded, it is still vulnerable and the attack can be repeated as long as the switch is IP reachable on port 23 and has not been upgraded to a fixed version of CatOS switch software.

This vulnerability is documented as Cisco bug ID CSCdw19195, which requires a CCO account to view and can be viewed after 2002 January 30 at 1500 UTC.

Vulnerability Scoring Details

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
http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html .

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at
http://intellishield.cisco.com/security/alertmanager/cvss .


Impact

This vulnerability can be exploited to produce a denial of service (DoS) attack. When the vulnerability is exploited it can cause the Cisco Catalyst switch to crash and reload.

Software Versions and Fixes

This vulnerability has been fixed in the following switch software revisions and the fix will be carried forward in all future releases.

Release 4 code base

Release 5 code base

Release 6 code base

Release 7 code base

Catalyst 6000 series

Not applicable

5.5(13) and later

6.3(4) and later

7.1(2) and later

Catalyst 5000 series

4.5(13a)

5.5(13) and later

6.3(4) and later

Not applicable

Catalyst 4000 series

Not available

5.5(13) and later

6.3(4) and later

7.1(2) and later

All previous releases must upgrade to the above releases. CatOS switch software release 4.5(13a) for the Catalyst 5000 series is expected on CCO by 2002 February 4. CatOS switch software release 7.1(2) is expected on CCO by 2002 February 6.

Software upgrade can be performed via the console interface. Please refer to software release notes for instructions.


Workarounds

The following workarounds can be implemented.

Obtaining Fixed Software

Cisco has made free software available to address this vulnerability for affected customers. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

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-center/sw-usingswc.shtml.

Do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades.

Customers with Service Contracts

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

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 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 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

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

Refer to 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 languages.

Exploitation and Public Announcements

This vulnerability has been exploited to initiate denial of service (DoS) attacks.

This vulnerability was reported by TESO and is detailed at http://www.cert.org/advisories/CA-2001-21.html.

Status of This Notice: Final

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.


Distribution

This advisory is posted on Cisco's Worldwide Web site at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20020129-catos-telrcv.

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 and Usenet news recipients.

  • cust-security-announce@cisco.com
  • bugtraq@securityfocus.com
  • firewalls@lists.gnac.com
  • first-teams@first.org (includes CERT/CC)
  • cisco@spot.colorado.edu
  • cisco-nsp@puck.nether.net
  • comp.dcom.sys.cisco
  • Various internal Cisco mailing lists

Future updates of this advisory, if any, will be placed on Cisco's Worldwide Web site, 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 1.2

2002-Feb-05

Minor Updates

Revision 1.1

2002-Jan-30

More Workarounds Added

Revision 1.0

2002-Jan-29

For Public Release 2002 January 29 at 1500 UTC

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/go/psirt. This includes instructions for press inquiries regarding Cisco security notices.


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