SSH tunnel in Browsers are easy! What about curl via SSH tunnels? Yeah – it`s easy, too!

Preparation

Check minimal firewall rules and SSH configuration on target host.

# ensure ssh service is enabled
$ firewall-cmd --list-services
...
ssh

# ensure AllowTcpForwarding is allowed
$ sshd -T | grep -i AllowTcpForwarding
...
allowtcpforwarding yes

Create SSH tunnel

Some basics about SSH tunnel…

# create ssh tunnel (foreground process)
$ ssh -ND localhost:9000 <user>@<host>
$ ssh -C4ND localhost:9000 <user>@<host>
$ ssh -C4ND localhost:9000 <user>@<host> -v
$ ssh -C4ND localhost:9000 <user>@<host> -p 22 -v

# create ssh tunnel (background process)
$ ssh -C4ND localhost:9000 <user>@<host> -f

• C: use compression (level can be set in configuration file)
• 4: forces ssh to use IPv4 only
• N: do not execute a remote command
• D: specifies dynamic application-level port forwarding
• v: verbose mode
• f: go to background before command execution
• p: port to connect to on the remote host

Check SSH tunnel

The following examples will help you to monitor the connection to the target server.

# check ssh tunnel (local)
$ ps aux | grep ssh

# check ssh tunnel via lsof (target)
$ lsof -nPi | grep ssh

# check ssh tunnel via ss (target)
$ ss -4t

Use SSH tunnel

Now we use the tunnel via curl. With the service ipinfo.io we can verify.

# curl for external ip (without tunnel)
$ curl https://ipinfo.io/ip

# curl for external ip
$ curl --socks5 localhost:9000 https://ipinfo.io/ip

# curl for external ip (since curl v7.21.7)
$ curl -x socks5://localhost:9000 https://ipinfo.io/ip

Note: There are two protocol prefixes socks5:// and socks5h://. The 2nd will let the SOCKS server handle DNS-queries.

Kill SSH tunnel

The simplest and hardest way to kill SSH tunnels (on background) is following example. But be careful it kills all ssh connections!

# kill all ssh tunnel
$ sudo killall ssh