sshtunnel.txt

# Inspired from:
# https://dev.to/bulletmark/create-a-reverse-ssh-tunnel-for-remote-access-to-a-restricted-machine-1ma0
# https://unix.stackexchange.com/questions/474848/ssh-remote-port-forwarding-with-multiple-ports

# ----------------------------------------------- #

# On local restricted machine to access
sudo mkdir -p /etc/sshtunnel && \
sudo ssh-keygen -qN "" -f /etc/sshtunnel/id_rsa && \
sudo vim /etc/systemd/system/sshtunnel.service

# BEGIN File content
[Unit]
Description=Service to maintain an ssh reverse tunnel
Wants=network-online.target
After=network-online.target
StartLimitIntervalSec=0

[Service]
Type=simple
ExecStart=/usr/bin/ssh -qgNn \
  -o ServerAliveInterval=30 \
  -o ServerAliveCountMax=3 \
  -o ExitOnForwardFailure=yes \
  -o StrictHostKeyChecking=no \
  -o UserKnownHostsFile=/dev/null \
  -o PreferredAuthentications=publickey \
  -i /etc/sshtunnel/id_rsa \
  -R 0.0.0.0:3389:localhost:3389 \
  -R 0.0.0.0:60022:localhost:22 \
  -R 0.0.0.0:8080:localhost:80 \
  -R 0.0.0.0:60443:localhost:443 \
  -R 0.0.0.0:10000:localhost:10000 \
  sshtunnel@domain.tld -p 22
Restart=always
RestartSec=60

[Install]
WantedBy=multi-user.target
# END File content

# Make sure to only use key authentication and
# disallow root login in /etc/ssh/sshd_config
PermitRootLogin no
PasswordAuthentication no
PermitEmptyPasswords no
ChallengeResponseAuthentication no

# ----------------------------------------------- #

# On the server used to tunnel connexions
sudo useradd -m -s /bin/true sshtunnel &&
sudo mkdir -p ~sshtunnel/.ssh &&
sudo vim ~sshtunnel/.ssh/authorized_keys
# paste the content of local id_rsa.pub in ~sshtunnel/.ssh/authorized_keys and save-quit
sudo chown -R sshtunnel:sshtunnel ~sshtunnel/.ssh && \
sudo chmod 700 ~sshtunnel/.ssh && \
sudo chmod 600 ~sshtunnel/.ssh/authorized_keys


# WARNING: Exposes the restricted machine's ssh access to the public Internet
# Make sure to use key authentication on the restricted machine!

# Set the following in /etc/ssh/sshd_config
GatewayPorts yes
AllowTcpForwarding yes

# Check with:
sshd -T | grep -E 'GatewayPorts|AllowTcpForwarding'

# Use after editing /etc/ssh/sshd_config
sudo systemctl restart ssh

# Edit /etc/apache2/sites-available/vhost-sub.domain.tld.conf
<VirtualHost *:80>
	ServerName vhost-sub.domain.tld

	Redirect permanent / "https://vhost-sub.domain.tld"
</VirtualHost>

<VirtualHost *:443>
	ServerName vhost-sub.domain.tld

	ProxyPreserveHost On
	ProxyRequests Off
	ProxyVia On
	RequestHeader set "X-Forwarded-Proto" expr=%{REQUEST_SCHEME}
            
	# Proxy all traffic to vhost-sub.domain.tld
	ProxyPass / http://localhost:60080/
	ProxyPassReverse / http://vhost-sub.domain.tld/
</VirtualHost>

# ----------------------------------------------- #

# On local restricted machine to access

sudo systemctl enable --now sshtunnel
sudo systemctl status sshtunnel
sudo journalctl -u sshtunnel

# ----------------------------------------------- #

# Removal

# On the restricted machine:
sudo systemctl disable --now sshtunnel
sudo rm /etc/systemd/system/sshtunnel.service
sudo rm -rf /etc/sshtunnel
# On the server:
sudo userdel -r sshtunnel

# Set the following in /etc/ssh/sshd_config
GateWayPorts no

# Use after editing /etc/ssh/sshd_config
sudo systemctl restart ssh