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Home : Advisories : Cisco Catalyst Memory Leak Vulnerability

Title: Cisco Catalyst Memory Leak Vulnerability
Released by: Cisco
Date: 6th December 2000
Printable version: Click here

Cisco Catalyst Memory Leak Vulnerability

Revision 1.0

For Release 2000 December 6 08:00 AM US/Pacific (UTC+0700)



A series of failed telnet authentication attempts to the switch can cause

the Catalyst Switch to fail to pass traffic or accept management

connections until the system is rebooted or a power cycle is performed. All

types of telnet authentication are affected, including Kerberized telnet,

and AAA authentication.

This vulnerability has been assigned Cisco bug ID CSCds66191.

The complete advisory can be viewed at


Affected Products

Catalyst 4000 and 5000 images running version  4.5(2) up to 5.5(4) and


Catalyst 6000 images running version 5.3(1)CSX, up to and including 5.5(4),


No other releases of Cisco Catalyst software are affected by this


No other Cisco products are affected by this vulnerability.


The telnet process fails to release resources upon a failed authentication,

or a successful login of extremely short duration such as a telnet from

within an automated script. This memory leak eventually results in the

failure of the switch to perform any other processes, such as forwarding

traffic or management; a power cycle or reboot is required for recovery.

The command "show process memory" will indicate increased "Holding" memory

after failed telnet authentication attempts. This value will not decrease

over time except when a reboot, reload, or power cycle occurs. This bug may

be triggered over a period of time in the course of normal operation by

legitimate users that occasionally fail authentication.

lt-6509-e> (enable) sh proc mem

Memory Used:   3974544

       Free:  15265168

      Total:  19239712

PID        TTY        Allocated  Freed      Holding    Process

- ---------- ---------- ---------- ---------- ---------- ---------------

1          -2         1707632    3488       1704144    Kernel and Idle

24         -2         16         0          16         telnetd


This vulnerability enables a Denial of Service attack on the Catalyst


Software Versions and Fixes

Cisco has made the following fixed software available to customers:

Catalyst Release 4.5(10) for Catalyst 4000 and 5000.

Catalyst Release 5.5(4b) for Catalyst 4000, 5000 and 6000.

The fix will be carried forward into all future releases.

Getting Fixed Software

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 through the Software Center on Cisco's Worldwide Web

site at http://www.cisco.com.

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)

   * e-mail: tac@cisco.com

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. Please do not contact either "psirt@cisco.com" or

"security-alert@cisco.com" for software upgrades.


There is no configuration workaround to eliminate the problem.  However, if

you are unable to upgrade to an unaffected version, you may use other

devices to strictly control or prohibit telnet access to the switch,

permitting only connections from your local network.

Access control lists on the switch can limit the remote exploitation of the

vulnerability.  To limit access to known hosts use the following commands:

    set ip permit enable telnet

    set ip permit  [mask]

Remote management of the switch can also be disabled.

The above workarounds are provided as an option; however, the

recommendation is to upgrade to fixed code as soon as possible.

Exploitation and Public Announcements

Cisco Systems knows of no public discussion nor active exploits involving

this vulnerability, which was reported by a customer who noted the memory


Status of This Notice: FINAL

This is a final field notice. Although Cisco cannot guarantee the accuracy

of all statements in this notice, all of the facts have been checked to the

best of our ability. Cisco does not anticipate issuing updated versions of

this notice unless there is some material change in the facts. Should there

be a significant change in the facts, Cisco may update this notice.


This notice will be posted on Cisco's Worldwide Web site at

http://www.cisco.com/warp/public/707/catalyst-memleak-pub.html. 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

   * Various internal Cisco mailing lists

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.

Revision History

 Revision 1.006-DEC-2000 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

Web site at

http://www.cisco.com/warp/public/707/sec_incident_response.html. This

includes instructions for press inquiries regarding Cisco security notices.


This notice is copyright 2000 by Cisco Systems, Inc. This notice may be

redistributed freely after the release date given at the top of the text,

provided that redistributed copies are complete and unmodified, including

all date and version information.



Version: PGP 6.0.2









(C) 1999-2000 All rights reserved.