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Cisco Security Advisory

Cisco Catalyst Supervisor Remote Reload

Advisory ID: cisco-sa-19990324-cat7161

Revision 1.2

For Public Release 1999 March 24 20:00  UTC (GMT)


A software bug (Cisco bug ID CSCdi74333) allows remote TCP/IP users to cause reloads of Cisco Catalyst LAN switches running Catalyst 5000 supervisor software versions from 1.0 through 2.1(5). The affected software was last shipped with new units in early 1997. In addition to the Catalyst 5xxx series, some, but not all, Catalyst 29xx family switches may run the affected software; see "Who is Affected" for more information.

A similar bug, Cisco bug ID CSCdj71684, exists in the supervisor software for the older, and now discontinued, Catalyst 12xx family, up through software version 4.29.

Fixes are available for both bugs. The fixes have been in the field for some time. Most Catalyst switch users have probably already installed the fixes.

This advisory is posted at

Affected Products

This section provides details on affected products.

Vulnerable Products

The following Cisco Catalyst LAN switch models are affected by this vulnerability--

  • The Catalyst 12xx family, running supervisor software versions up to and including 4.29.
  • The Catalyst 29xx family (but not the Catalyst 2900XL), running supervisor software versions up to and including 2.1(5), 2.1(501), and 2.1(502). This includes the Catalyst 2901, 2902, and 2903 switches. Catalyst 2926 switches are not affected, because the Catalyst 2926 was not released until after the software fix was made. Catalyst 2900XL switches run unrelated software, and are not affected by this vulnerability.
  • The Catalyst 5xxx series (including the Catalyst 55xx family), running supervisor software versions up to and including 2.1(5), 2.1(501), and 2.1(502).

Fixed software for the Catalyst 5xxx and Catalyst 29xx series began shipping with new switches in mid-1997. Sales of the Catalyst 12xx family were stopped before the release of software version 4.30; if you have not upgraded your software since installing your Catalyst 12xx switch, you are affected by this vulnerability.

The affected Cisco Catalyst LAN switches are rack-mountable units typically found in data centers and cable closets.

Products Confirmed Not Vulnerable

Catalyst 5xxx and 29xx switches running versions 2.1(6) and later are not affected. Catalyst 12xx switches running versions 4.30 and later are not affected. Some Cisco Catalyst switches include intelligent modules that run software independent of the supervisor software. These modules, which include a variety of media controllers as well as the route switch module (RSM), are not affected.

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


For the Catalyst 29xx and Catalyst 5xxx switches, this vulnerability has Cisco bug ID CSCdi74333. The bug is present in all supervisor software versions through 2.1(5), including the spot fix releases 2.1(501) and 2.1(502). The bug is fixed in 2.1(6) and later versions, including all 2.2, 2.3, and 2.4 versions, and all 3.x, 4.x, and later versions.

For the Catalyst 1200, this vulnerability has Cisco bug ID CSCdj71684. The bug is present in all software versions through 4.29, and is fixed in 4.30 and later versions.

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 .

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at .


A remote attacker who knows how to exploit this vulnerability, and who can make a connection to TCP port 7161 on an affected switch, can cause the supervisor module of that switch to reload. While the supervisor is reloading, the switch will not forward traffic, and the attack will therefore deny service to the equipment attached to the switch. The switch will recover automatically, but repeated attacks can extend the denial of service indefinitely.

Software Versions and Fixes

When considering software upgrades, also consult and any subsequent advisories to determine exposure and a complete upgrade solution.

In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center ("TAC") or your contracted maintenance provider for assistance.


This vulnerability may be worked around by assigning no IP addresses to affected Cisco Catalyst switches. However, this workaround will have the effect of disabling all remote management of those switches.

Another possible workaround is to use the filtering capabilities of surrounding routers and/or dedicated firewall devices to prevent untrusted hosts from making connections to TCP port 7161 on affected switches.

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, or as otherwise set forth at Downloads at

Do not contact either "" or "" 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

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 in obtaining fixed software through their point of sale should obtain software patches and bug fixes 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:

Have your product serial number available and provide the URL of this notice as evidence of entitlement to a software patch or bug fix. Customers without service contracts should request a software patch or bug fix through the TAC.

Refer to 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

Cisco knows of no public announcements or discussion of this vulnerability before the date of this notice. Cisco has had no reports of malicious exploitation of this vulnerability. These bugs were identified and reported by outside companies conducting laboratory testing.

No special tools, and only the most basic of skills, are needed to exploit this vulnerability. It would not be difficult for a person with minimal sophistication to find a way to exploit this vulnerability.

Cisco thanks the Internet Security Systems (ISS) X-Force, for independently discovering this matter and bringing it to the attention of Cisco's Product Security Incident Response Team (PSIRT).

The initial report of CSCdi74333 was received before the establishment of the PSIRT, from a customer who has neither requested credit nor given permission to be named in this notice. Cisco security notices do not name or credit third parties without their specific permission.

Status of This Notice: Final


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 and Usenet news recipients.

  • (includes CERT/CC)
  • Various internal Cisco mailing lists

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, 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


Initial public release.

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 This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at

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