Wireguard and iptables restrictions for multiple users

README.md

Wireguard and iptables restrictions for multiple users

If you don't know what Wireguard is, well, you should. It's fast, easy to setup and highly configurable. We will configure Wireguard for multiple users with various restrictions using iptables.

Assumptions

This should fit most setups (not mine though 😉)

• LAN network: 192.168.1.0/24 (192.168.1.1 => 192.168.1.254)
• LAN DNS server address: 192.168.1.1
• Wireguard is installed (kernel and tools) on a Linux host (it should also work on other platforms though).
• The Linux host address: 192.168.1.10
• The Linux host main interface: enp4s0 (find it with ip a)

Initial server setup

1. Ensure your iptables firewall has its FORWARD table policy set to DROP:

   iptables -P FORWARD -j DROP

2. Generate a Wireguard private key

   echo "Private key: $(wg genkey)"

   Private key: OM5BUrGVAswOm/r8asLtdUgJB8rrXflD6TVFL5aGAHk=
   

3. Create a file /etc/wireguard/wg0.conf (or any other name than wg0) with content:

   [Interface]
   Address = 10.0.0.1/24
   ListenPort = 51820
   PrivateKey = OM5BUrGVAswOm/r8asLtdUgJB8rrXflD6TVFL5aGAHk=
   PostUp = /etc/wireguard/postup.sh
   PostDown = /etc/wireguard/postdown.sh
   

   Don't forget to replace the PrivateKey value with the one you generated

4. Create a file /etc/wireguard/postup.sh with content:

   WIREGUARD_INTERFACE=wg0
   WIREGUARD_LAN=10.0.0.0/24
   MASQUERADE_INTERFACE=enp4s0
   
   iptables -t nat -I POSTROUTING -o $MASQUERADE_INTERFACE -j MASQUERADE -s $WIREGUARD_LAN
   
   # Add a WIREGUARD_wg0 chain to the FORWARD chain
   CHAIN_NAME="WIREGUARD_$WIREGUARD_INTERFACE"
   iptables -N $CHAIN_NAME
   iptables -A FORWARD -j $CHAIN_NAME
   
   # Accept related or established traffic
   iptables -A $CHAIN_NAME -o $WIREGUARD_INTERFACE -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
   
   # Accept traffic from any Wireguard IP address connected to the Wireguard server
   iptables -A $CHAIN_NAME -s $WIREGUARD_LAN -i $WIREGUARD_INTERFACE -j ACCEPT
   
   # Drop everything else coming through the Wireguard interface
   iptables -A $CHAIN_NAME -i $WIREGUARD_INTERFACE -j DROP
   
   # Return to FORWARD chain
   iptables -A $CHAIN_NAME -j RETURN

5. Create a file /etc/wireguard/postdown.sh with content:

   WIREGUARD_INTERFACE=wg0
   WIREGUARD_LAN=10.0.0.0/24
   MASQUERADE_INTERFACE=enp4s0
   CHAIN_NAME="WIREGUARD_$WIREGUARD_INTERFACE"
   
   iptables -t nat -D POSTROUTING -o $MASQUERADE_INTERFACE -j MASQUERADE -s $WIREGUARD_LAN
   
   # Remove and delete the WIREGUARD_wg0 chain
   iptables -D FORWARD -j $CHAIN_NAME
   iptables -F $CHAIN_NAME
   iptables -X $CHAIN_NAME

First admin client

Let's setup a client with full access to Internet and your LAN through Wireguard.

1. Install Wireguard on your client device

2. On your client device, create a configuration file client.conf with content:

   [Interface]
   Address = 10.0.0.2/32
   DNS = 192.168.1.1
   PrivateKey = YOUR_CLIENT_PRIVATE_KEY
   
   [Peer]
   AllowedIPs = 0.0.0.0/0, ::/0
   Endpoint = 192.168.1.10:51820
   PersistentKeepalive = 25
   PublicKey = YOUR_SERVER_PUBLIC_KEY
   

3. Replace in the configuration above YOUR_SERVER_PUBLIC_KEY with the key shown using wg show wg0 public-key on your server. For example: p6aGalk69yCM8vNhbvC5mEH/HhJr1c8f55UaeJSChX0=.

4. Generate keys for your client:

   priv=`wg genkey` && printf "Private key: $priv\nPublic key: `echo "$priv" | wg pubkey`\n" && unset -v priv

   Private key: 2L4L8YwusK4Ot4jVoo/1wwQfLAeRM6kJ/WWxzfnWKm4=
   Public key: GmVyaj+K36xEk7ko/8jijMB9XX9dFgi4mJxsAEFMHmA=
   

5. Replace in client.conf YOUR_CLIENT_PRIVATE_KEY with the private key just generated above.

6. Use the public key shown above to add the following block to /etc/wireguard/wg0.conf on your server:

   [Peer]
   # Your first admin client
   PublicKey = GmVyaj+K36xEk7ko/8jijMB9XX9dFgi4mJxsAEFMHmA=
   AllowedIPs = 10.0.0.2/32
   

7. On your server, start Wireguard: wg-quick up wg0.

8. You should now be able to connect to the Wireguard server from your client. You can check on the server with wg and it should show a latest handshake line.

LAN only user

Let's add a user who should only have access to the LAN.

1. Repeat steps 1 to 5 from the First admin client section above.

2. Use the public key shown in step 4 to add the following block to /etc/wireguard/wg0.conf on your server:

   [Peer]
   # LAN only user
   PublicKey = 7GneIV/Od7WEKfTpIXr+rTzPf3okaQTBwsfBs5Eqiyw=
   AllowedIPs = 10.0.0.3/32
   

3. Shutdown Wireguard: wg-quick down wg0

4. Modify /etc/wireguard/postup.sh:

   • Limit full access to our first admin client 10.0.0.2 only by changing:

     iptables -A $CHAIN_NAME -s 10.0.0.0/24 -i $WIREGUARD_INTERFACE -j ACCEPT

     to

     iptables -A $CHAIN_NAME -s 10.0.0.2 -i $WIREGUARD_INTERFACE -j ACCEPT

   • Add a new line to allow our new user to LAN access only

     iptables -A $CHAIN_NAME -s 10.0.0.3 -i $WIREGUARD_INTERFACE -d 192.168.1.0/24 -j ACCEPT

5. Start Wireguard: wg-quick up wg0

6. Note that the client should set its AllowedIPs = 0.0.0.0/0, ::/0 to AllowedIPs = 192.168.1.0/24 so it tunnels only to when trying to reach an address on the LAN.

Restrict the user to a port

Let's re-use the user we previously created. Let's only allow him to access port 445 (Samba) on a server 192.168.1.20 for example.

1. Shutdown Wireguard: wg-quick down wg0

2. Modify

   iptables -A $CHAIN_NAME -s 10.0.0.3 -i $WIREGUARD_INTERFACE -d 192.168.1.0/24 -j ACCEPT

   to

   iptables -A $CHAIN_NAME -s 10.0.0.3 -i $WIREGUARD_INTERFACE -d 192.168.10.20 -p tcp --dport 445 -j ACCEPT

3. Start Wireguard: wg-quick up wg0

Restrict the user to limited Web browsing only

That's useful for our friends who want to stream restricted content on Netflix without allowing them on your LAN 😉

1. Shutdown Wireguard: wg-quick down wg0

2. Modify

   iptables -A $CHAIN_NAME -s 10.0.0.3 -i $WIREGUARD_INTERFACE -d 192.168.10.20 -p tcp --dport 445 -j ACCEPT

   to

   # DNS
   iptables -A $CHAIN_NAME -s 10.0.0.3 -i $WIREGUARD_INTERFACE -d 192.168.1.1 -p udp --dport 53 -j ACCEPT
   # Drop traffic to your any private IP address
   iptables -A $CHAIN_NAME -s 10.0.0.3 -i $WIREGUARD_INTERFACE -d 10.0.0.0/8,172.16.0.0/12,192.168.0.0/16 -j DROP
   # Accept outgoing connections to HTTP(S) ports to any IP address (public because of rule above)
   iptables -A $CHAIN_NAME -s 10.0.0.3 -i $WIREGUARD_INTERFACE -d 0.0.0.0/0 -p tcp -m multiport --dports 80,443 -j ACCEPT

3. Start Wireguard: wg-quick up wg0

4. Don't forget to set back the client to AllowedIPs = 0.0.0.0/0, ::/0

More rules

Feel free to comment, I'll try my best to make you a rule 😉

Enjoy!