Software Engineering Institute

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.

Workarounds

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.