The SSH client must not permit tunnels.

From VMware ESXi Server 5.0 Security Technical Implementation Guide

Associated with: CCI-000366

SV-51086r3_rule The SSH client must not permit tunnels.

Vulnerability discussion

OpenSSH has the ability to create network tunnels (layer-2 and layer-3) over an SSH connection. This function can provide similar convenience to a Virtual Private Network (VPN) with the similar risk of providing a path to circumvent firewalls and network ACLs.

Check content

Disable lock down mode. Enable the ESXi Shell. Execute the following command(s): # grep Tunnel /etc/ssh/ssh_config If the "Tunnel" attribute is not set to "no", this is a finding. If the /etc/ssh/ssh_config file does not exist or the Tunnel option is not set, this is not a finding. Re-enable lock down mode.

Fix text

Disable lock down mode. Enable the ESXi Shell. Execute the following command(s): # vi /etc/ssh/ssh_config Add/modify the attribute line entry to the following (quotes for emphasis only): "Tunnel no" Re-enable lock down mode.

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