Products & Services

Contents

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

This section provides details on affected products.

Vulnerable Products

Products Confirmed Not Vulnerable

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.

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.

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

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.

The following workarounds can be implemented.

• If the ssh feature is available in the code base, use ssh instead of Telnet and disable Telnet.
  For instructions on how to do this, please refer to http://www.cisco.com/warp/public/707/ssh_cat_switches.html.
  
• Apply IP Permit List for Telnet to enable access to the switch's management interface only from the network management workstations.
  For instructions on how to do this, please refer to http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_6_3/config/ip_perm.htm.
  Please note, this 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.
  
• On the Catalyst 6000 series switches, if the VLAN Access Control List (ACL) (VACL) feature is available in the code base, you can use VACLs instead of the IP Permit List workaround above.
  For instructions on how to do this, please refer to http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/catos/6.x/configuration/guide/acc_list.html.
  Please note, this 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.
  
• Implement the best practice to assign all of the management interfaces of all the switches in the network to a different VLAN, and apply appropriate ACLs on the router switching between the VLANs.
  For an example, see http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/catos/6.x/configuration/guide/acc_list.html.
  
• Apply ACLs on routers / switches / firewalls in front of the vulnerable switches such that traffic destined for the Telnet port 23 on the vulnerable switches is only allowed from the network management workstations.
  For an example, see http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/catos/6.x/configuration/guide/acc_list.html.
  

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 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 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 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.

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.

This advisory is posted on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/cisco-sa-20020129-catos-telrcv.shtml.

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.

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.