Title

The SSH daemon must not permit tunnels. (Cat II impact)

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

Check the SSH daemon configuration for the PermitTunnel setting. # grep -i PermitTunnel /etc/ssh/sshd_config | grep -v '^#' If the setting is not present, or set to yes, this is a finding.

Fix Text

Edit the SSH daemon configuration and add or edit the PermitTunnel setting value to no.

Additional Identifiers

Rule ID: SV-26774r1_rule

Vulnerability ID: V-22480

Group Title: GEN005531

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.