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TUCoPS :: Cisco :: ciacl068.txt

Cisco vpn3000 concentrator vulnerability


                       The U.S. Department of Energy
                     Computer Incident Advisory Center
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___

                             INFORMATION BULLETIN

                Cisco VPN3000 Concentrator TELNET Vulnerability

April 6, 2001 19:00 GMT                                           Number L-068
PROBLEM:       The SSL and telnet connections are not handled properly for 
               failed logon attempts. 
PLATFORM:      Cisco VPN 3000 series concentrators running software releases 
               up to but not including version 3.0.00 are affected by this 
               vulnerability. This series includes models 3005, 3015, 3030, 
               3060, and 3080. 
DAMAGE:        A flood of data sent to either the SSL or telnet port can cause 
               Cisco VPN 3000 series concentrators to reboot. The concentrator 
               will reboot each time the port is flooded with data. This 
               results in a denial of service (DoS) condition. 
SOLUTION:      To determine if a Cisco VPN 3000 series concentrator is running 
               affected software, check version via the web interface or the 
               console login. If the system requires patching, follow Cisco 
               instructions for obtaining the patch. 
VULNERABILITY  The risk is LOW. There have been no reports of this DoS in the 
ASSESSMENT:    wild. 

[******  Begin Cisco Bulletin  ******]

Cisco Security Advisory: VPN3000 Concentrator TELNET Vulnerability
Revision 1.0

For Public Release 2001 March 28 08:00 (UTC -0800)



Sending a flood of data to the SSL or regular telnet port can cause the
Cisco VPN 3000 series concentrators to reboot. After rebooting, the
equipment would function normally until the flood of data is sent again.

To remove the vulnerability, Cisco is offering free software upgrades to
revision 3.0.00 for all affected platforms. The defect is described in DDTS
record CSCds90807.

This notice will be posted at

Affected Products

Cisco VPN 3000 series concentrators running software releases up to but not
including version 3.0.00 are affected by this vulnerability. This series
includes models 3005, 3015, 3030, 3060, and 3080.

Any model running version 3.0.00 or later is unaffected.

This vulnerability does not affect the VPN 5000 series concentrators. No
other Cisco product is affected by this vulnerability.

To determine if a Cisco VPN 3000 series concentrator is running affected
software, check version via the web interface or the console login.


The vulnerability occurs because the SSL or regular telnet session does not
disconnect after repeated failed attempts and the system keeps trying to
interpret the data coming in on the SSL or regular telnet port. Therefore,
data coming in at an uncontrolled rate can flood the telnet queues causing
a shortage of memory on the system resulting in a reboot. This has been
fixed by ensuring that a SSL or regular telnet session is terminated after
three repeated failed attempts. The vulnerability is documented as DDTS


Sending a flood of data to the SSL or regular telnet port can cause the VPN
3000 series concentrators to reboot. While reloading, the device cannot
handle any traffic. Repeatedly causing the affected device to reload will
result in a denial of service, thus affecting the availability of the

SSL and regular telnet service on the external interface is disabled by

Software Versions and Fixes

The vulnerability has been fixed in revision 3.0.00 code. The fix will be
carried forward into all future releases.

Obtaining Fixed Software

Cisco is offering free software upgrades to eliminate 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 via Cisco's Software Center at

Customers without contracts or warranty should get their upgrades by
contacting the Cisco Technical Assistance Center (TAC) as shown below:

   * (800) 553-2447 (toll-free in North America)
   * +1 408 526 7209 (toll call from anywhere in the world)
   * e-mail:

See for
additional TAC contact information, including instructions and e-mail
addresses for use in various languages.

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 "" or
"" for software upgrades; faster results will be
obtained by contacting the TAC directly.


The vulnerability can be avoided by disabling all Telnet access to the
equipment until you upgrade.

There are two ways to disallow telnet on any given interface - you can use
a filter whose rules don't allow telnet, or by creating a rule that
specifically denies telnet access and applying that to your existing
Further details can be found at the this URL


After disabling SSL and regular telnet the equipment can be managed via the
console port or via browser access.

Exploitation and Public Announcements

The Cisco PSIRT is not aware of any public announcements or malicious use
of the vulnerabilities described in this advisory.
This was reported to Cisco by a customer who discovered this vulnerability
as a side effect of using a SSL telnet tool.

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

In addition to Worldwide Web posting, a text version of this notice will be
clear-signed with the Cisco PSIRT PGP key and will be posted to the
following e-mail and Usenet news recipients:

   * (including CERT/CC)
   * 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   2001-03-28Initial 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 This
includes instructions for press inquiries regarding Cisco security notices.

This notice is Copyright 2001 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, and include
all date and version information.


All contents are Copyright  1992--2001 Cisco Systems Inc. All rights
reserved. Important Notices and Privacy Statement.

[******  End Cisco Bulletin  *****]

CIAC wishes to acknowledge the contributions of Cisco Systems, Inc. for the 
information contained in this bulletin.

CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
Institutes of Health (NIH). CIAC is located at the Lawrence Livermore
National Laboratory in Livermore, California. CIAC is also a founding
member of FIRST, the Forum of Incident Response and Security Teams, a
global organization established to foster cooperation and coordination
among computer security teams worldwide.

CIAC services are available to DOE, DOE contractors, and the NIH. CIAC
can be contacted at:
    Voice:    +1 925-422-8193 (7x24)
    FAX:      +1 925-423-8002
    STU-III:  +1 925-423-2604

Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.

   World Wide Web:
                        (or -- they're the same machine)
   Anonymous FTP:
                        (or -- they're the same machine)

PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
communities receive CIAC bulletins.  If you are not part of these
communities, please contact your agency's response team to report
incidents. Your agency's team will coordinate with CIAC. The Forum of
Incident Response and Security Teams (FIRST) is a world-wide
organization. A list of FIRST member organizations and their
constituencies can be obtained via WWW at

This document was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor the University of California nor any of their
employees, makes any warranty, express or implied, or assumes any
legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately
owned rights. Reference herein to any specific commercial products,
process, or service by trade name, trademark, manufacturer, or
otherwise, does not necessarily constitute or imply its endorsement,
recommendation or favoring by the United States Government or the
University of California. The views and opinions of authors expressed
herein do not necessarily state or reflect those of the United States
Government or the University of California, and shall not be used for
advertising or product endorsement purposes.

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