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CERT Coordination Center

Cisco VPN 3000 Concentrator forces device to reload when processing malformed SSH initialization packet

Vulnerability Note VU#317348

Original Release Date: 2003-06-23 | Last Revised: 2003-06-23


A vulnerability in some Cisco Virtual Private Network (VPN) products could allow a remote attacker to cause a denial of service.


The Cisco VPN 3000 Series Concentrators and the Cisco VPN 3002 Hardware Clients are Virtual Private Network (VPN) platforms designed to provide secure remote network access. Some models of these devices contain a vulnerability by which a malformed SSH initialization packet sent during the initial SSH session setup may reload the VPN 3000 series concentrator.


A denial-of-service condition can result from unexpected rebooting of the affected device.


Cisco Systems Inc. has released software patches and workaround information for this vulnerability. Please see the vendor information section of this document for more details.


Restrict access to the SSH server on the VPN concentrator by applying appropriate rules to the filters for the interfaces such that connections are permitted only from trusted client hosts. Sites may additionally wish to filter SSH connections on network devices that are upstream from the affected VPN Concentrator device. Sites may wish to apply this workaround in conjunction with the application of the recommended patches. As a general rule, the CERT/CC recommends that sites block all types of network traffic that are not explicitly required for normal operation.

Vendor Information


Cisco Systems Inc. Affected

Updated:  May 08, 2003



Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


Cisco Systems Inc. has released Cisco Security Advisory 20030507-vpn3k in response to this issue. Users are encouraged to review this advisory and apply the patches and workarounds it recommends.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

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Thanks to Cisco Systems Product Security Incident Response Team for reporting this vulnerability.

This document was written by Chad R Dougherty.

Other Information

CVE IDs: CVE-2003-0259
Severity Metric: 6.75
Date Public: 2003-05-07
Date First Published: 2003-06-23
Date Last Updated: 2003-06-23 18:13 UTC
Document Revision: 10

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