Cisco Security Advisory

Denial-of-Service of TCP-based Services in CatOS

Advisory ID: cisco-sa-20030709-swtcp

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20030709-swtcp

Revision 1.5

For Public Release 2003 July 9 16:00  UTC (GMT)


Summary

After receiving eight TCP connection attempts using a non-standard TCP flags combination, a Catalyst switch will stop responding to further TCP connections to that particular service. In order to re-establish functionality of that service, the switch must be rebooted. There is no workaround. This vulnerability affects only CatOS. No other Cisco products are affected.

This advisory is available at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20030709-swtcp.

Affected Products

Vulnerable Products

The CatOS for the following Catalyst models are affected:

  • Catalyst 4000 Series including models 2948G and 2980G/2980G-A 
  • Catalyst 5000 Series including models 2901, 2902 and 2926 
  • Catalyst 6000 

Products Confirmed Not Vulnerable

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

Details

After receiving eight connection attempts on any TCP service, the switch will stop responding to any further connection attempts to that service. These attempts must use a non-standard combination of TCP flags. The switch will continue to pass other switched traffic normally and the console is also not affected. Only the service to which connections were made will become unresponsive. Standard TCP services include HTTP, Telnet, and SSH.

This vulnerability is documented as Cisco Bug ID CSCdw52219 ( registered customers only) .

Vulnerability Scoring Details

Cisco has not provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS).  At the time of original publication, CVSS scoring in Cisco security publications was not yet adopted.

Impact

By exploiting this vulnerability, an attacker can prevent further use of the specified TCP-based service. Depending on the configuration of the device, if SSH or Telnet are enabled and exploited, the availability of those services could be affected, possibly resulting in a loss of management capability using those same services. However, UDP-based services such as Simple Network Management Protocol (SNMP) would still be available and unaffected.

Software Versions and Fixes

The vulnerability is fixed in the following releases. All previous releases are vulnerable and all higher releases, from the ones in the table, are fixed.

Train

Description of Image or Platform

Availability of Fixed Releases*

   

Rebuild

Interim**

Maintenance

4.x

Catalyst 4000, 5000

Affected, no fix planned

4.5

Catalyst 4000, 5000

 

4.5(13.1)

4.5(14)

5.1

Catalyst 4000, 5000, 6000

Affected, no fix planned

5.2

Catalyst 4000, 5000, 6000

Affected, no fix planned

5.3

Catalyst 6000

Affected, no fix planned

5.4

Catalyst 4000, 5000, 6000

Affected, no fix planned

5.5

Catalyst 4000, 5000, 6000

 

5.5(13.5)

5.5(14)

6.1

Catalyst 4000, 5000, 6000

Affected, no fix planned

6.2

Catalyst 4000, 5000, 6000

Affected, no fix planned

6.3

Catalyst 4000, 5000, 6000

 

6.3(5.10)

6.3(6)

6.4

Catalyst 4000, 5000, 6000

Not affected

7.1

Catalyst 4000, 6000

Affected, no fix planned

7.2

Catalyst 4000, 6000

 

7.2(0.65)

7.2(1)

7.3

Catalyst 4000, 6000

Not affected

7.4

Catalyst 4000, 6000

 

7.4(0.2)CLR

7.4(1)

7.5

Catalyst 4000, 6000

Not affected

7.6

Catalyst 4000, 6000

Not affected

8.1

Catalyst 6000

Not affected

* All dates are estimates and subject to change.

** Interim releases are subjected to less rigorous testing than regular maintenance releases, and may have serious bugs.


Workarounds

There is no workaround. In order to continue using an affected TCP service, the switch must be rebooted.

It is possible to mitigate the exposure by configuring VLAN Access Control Lists (VACLs) on the switch (where they are supported) that will allow only legitimate hosts to connect to the desired services. This must be combined with Unicast Reverse Path Forwarding (uRPF), or some other anti-spoofing technique, on the network edge to protect against spoofed packets from the outside of the network.

Obtaining Fixed Software

Cisco has released free software updates that address these vulnerabilities. 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/en/US/docs/general/warranty/English/EU1KEN_.html , or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml .

Do not contact 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 agreements 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 do not hold a Cisco service contract, and customers who purchase through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should acquire 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

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

Refer to http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html for additional TAC contact information, including localized telephone numbers, and instructions and e-mail addresses for use in various languages.

Exploitation and Public Announcements

This vulnerability has been reported to Cisco by a customer. The Cisco PSIRT has received no reports of malicious exploitation of this vulnerability and we are not aware of any public discussion.

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 will be posted on the Cisco Worldwide Web site at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20030709-swtcp.

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 
  • first-teams@first.org (includes CERT/CC) 
  • cisco@spot.colorado.edu 
  • comp.dcom.sys.cisco 
  • firewalls@lists.gnac.com 
  • Various internal Cisco mailing lists 

Future updates of this advisory, if any, will be placed on the Cisco 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.


Revision History

Revision 1.0

2003-July-09 16:00 UTC (GMT)

Initial public release

Revision 1.1

2003-July-10 18:00 UTC (GMT)

Added 4.x, 6.1, 6.2 and 7.1 releases to the "Software Versions and Fixes" table

Revision 1.2

2003-July-14 20:30 UTC (GMT)

Added 5.1, 5.2, 5.3, 5.4, and 7.3 to the "Software Versions and Fixes" table

Revision 1.3

2003-July-15 20:30 UTC (GMT)

Added 7.5 and 7.6 to the "Software Versions and Fixes" table

Revision 1.4

2003-July-28 22:00 UTC (GMT)

Corrected description field for CatOS 7.1 in the "Software Versions and Fixes" table

Revision 1.5

2003-September-08 12:24 UTC (GMT)

Added 4.5 to the "Software Versions and Fixes" table

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/web/about/security/psirt/security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.


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