VPN Sidedoor

Quick and dirty script for listening services to maintain a route back to the default gateway when connecting to a VPN.

Useful for SSH tunneling through a VPN connection on a remote system.

Run the script before starting the VPN Client. Once run, listening services will remain remotely accessible whilst any tunneled traffic will route through the tun0 adapter.

To configure route on a specific network adapter

$ sudo vpn-sidedoor.sh <adapter>

Example on eth0

$ sudo vpn-sidedoor.sh eth0

Omitting the <adapter> will enable the route on the first network adapter in the UP state.

$ sudo vpn-sidedoor.sh

Example SSH Config file ~/.ssh/config:

Host vpn-tunnel
        HostName 1.2.3.4
        Port 22
        User ubuntu
        IdentityFile ~/.ssh/vpn-tunnel.pem
        DynamicForward 1080

Host target-bastion
        HostName bastion.example.com
        Port 22
        User tester
        IdentityFile ~/.ssh/example/bastion.pem
        ProxyCommand ssh -q -W %h:%p vpn-tunnel
        # Optional: Uncomment below for proxychains-ng
        # DynamicForward 9050
        # LogLevel QUIET

Host *
        ServerAliveInterval 60