ncik20

Setting up WireGuard vpn to work in restricted networks that block UDP traffic.

• vpn
• wireguard

Basic Idea

• Run wstunnel to tunnel UDP traffic to vpn server
• Configure local wg-quick to use localhost as endpoint

Sounds easy, and it’s not hard, but there are some gotchas to be aware off:

• Have to do your own routing setup
• Possible issues with DNS when wstunnel needs to re-connect

Prerequisite

I’m going to assume that you have already got WireGuard working over UDP with Linux server in the cloud and MacOS client. If not, there are plenty of guides on-line. For me the main stumbling block was not realising early enough that even though WireGuard itself doesn’t have a concept of server/client, the way you configure the server and the way you configure clients is actually somewhat different. On a client side you have a single peer with the public key of your server and with Endpoint pointing to the domain of your server, you also probably want to configure DNS.

Something like this example:

[Interface]
PrivateKey = oCkFT5ZmTJZapiCm2zZ/vNRhdVRFhKFhnkVFKRJW+2U=
Address = 10.10.0.2/24
DNS = 1.1.1.1
DNS = 8.8.8.8

[Peer]
PublicKey = xWdX6PjqZPG+So5ndzgjBa3OxSEgPA5Exi+GMLknHWA=
AllowedIPs = 0.0.0.0/0, ::0
Endpoint = yourhost.tld:51820

The important part above is AllowedIPs = 0.0.0.0/0, ::0, which tells wg-quick to route all the traffic (v4 and v6) through the tunnel when setting up the connection. Also you should avoid using SaveConfig option on the client side as it will overwrite domain name of the server with IP address, which is probably not what you want.

On the server side things might look something like this:

[Interface]
PrivateKey = AL7WeXT59GebMA5RLnI97fMarjKS1dnSFIDCLhxTymE=
Address = 10.10.0.1/24
PostUp = iptables -A FORWARD -i %i -j ACCEPT; iptables -t nat -A POSTROUTING -o ens3 -j MASQUERADE
PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -t nat -D POSTROUTING -o ens3 -j MASQUERADE
ListenPort = 51820

[Peer]
PublicKey = kAodaLwCyX6t4Olxh0r6/ohxoIvYTQ24QIT/sijAAB0=
AllowedIPs = 10.10.0.2/32

[Peer]
...

Note differences in the [Interface] section, it includes PostUp/PostDown rules to setup/tear down packet forwarding from the wireguard interface (%i) to your main network interface (ens3 in this case). There is also ListenPort directive and no DNS.

In the [Peer] section, AllowedIPs is set to the value of Interface.Address in the client config file, also Endpoint is omitted. Each peer has to have unique address, and different from that of a server.

UDP Tunnel

Head over to wstunnel releases and download linux version for your server and MacOS version for the client.

On a server we run

wstunnel -v -s wss://0.0.0.0/ --restrictTo 127.0.0.1:51820

This will listen for a TLS connection on port 443 and will only forward packets destined to a localhost and wireguard port.

Client will run this:

wstunnel -v --udp --udpTimeoutSec -1 -L 127.0.0.1:51820:127.0.0.1:51820 wss://yourhost.tld/

This will listen on port 51820 on localhost only and forward these packets to port 51280 on yourhost.tld.

Nginx as Proxy

If you would like to run webserver on the same machine that runs wstunnel then you don’t want port 443 to be used solely for UDP tunnelling. With nginx, websockets tunnelling is possible with a configuration similar to below:

You will then run wstunnel server on port 33344, binding to localhost and without TLS:

wstunnel --server ws://127.0.0.1:33344 --restrictTo=127.0.0.1:51820

You probably want to make this auto-start on your server:

Extra advantage you gain by using nginx as reverse proxy is a kind of “authentication”. Only requests made to https://yourhost.tld/{longish-random-string}/... will be forwarded to wstunnel server, and since we are using TLS {longish-random-string} shouldn’t be visible to any middleman. You also get access logs and proper TLS (wstunnel only has one hard-coded certificate).

Configure wg-quick to use UDP Tunnel

Copy wg0.conf into wg1.conf and make this change

[Peer]
PublicKey = xWdX6PjqZPG+So5ndzgjBa3OxSEgPA5Exi+GMLknHWA=
AllowedIPs = 0.0.0.0/0, ::0
- Endpoint = yourhost.tld:51820
+ Endpoint = 127.0.0.1:51820

If at this point you try wg-quick up wg1, things won’t work for the following reasons:

1. wg-quick
   

   will route all traffic through tunnel including traffic to

   yourhost.tld
   

   • We can solve this by adding custom route to yourhost.tld in PreUp

2. wg-quick
   

   will route all traffic to

   127.0.0.1
   

   through your default gateway, and so won’t be able to talk to

   wstunnel
   

   in the first place

   • No easy solution to this one, have to disable routing within wg-quick altogether with Table = off option, then setup routing manually

3. wstunnel
   

   will fail to connect due to DNS failure, since DNS traffic will be routed through a tunnel that hasn’t been established yet. This might not happen right away due to DNS caching, but will become a problem when trying to re-connect

   • Option 1: use IP address of the server on a client side, downside no vhost routing if using nginx, no TLS verification.
   • Option 2: write current server IP to /etc/hosts
   • Option 3: run dnsmasq on client side, configure dnsmasq rather than /etc/hosts

I have written this script that helps with setting up correct routes, launching wstunnel and updating /etc/hosts. To use it copy it to /etc/wireguard/ directory and add the following to your [Interface] section of wg1.conf

[Interface]
PrivateKey = oCkFT5ZmTJZapiCm2zZ/vNRhdVRFhKFhnkVFKRJW+2U=
+ Table = off
+ PreUp = source /etc/wireguard/wstunnel.sh && pre_up %I
+ PostUp = source /etc/wireguard/wstunnel.sh && post_up %i %I
+ PostDown = source /etc/wireguard/wstunnel.sh && post_down %i %I

Setup script reads configuration from /etc/wireguard/{wg_interface}.wstunnel

REMOTE_HOST=yourhost.tld
REMOTE_PORT=51820
UPDATE_HOSTS='/etc/hosts'
# if using nginx with custom prefix for added security, configure it here
WS_PREFIX='E7m5vGDqryd55MMP'

# Can change local port of the wstunnel, don't forget to change Peer.Endpoint
#LOCAL_PORT=${REMOTE_PORT}

# If using dnsmasq can supply other file than /etc/hosts
# UPDATE_HOSTS='/usr/local/etc/dnsmasq.d/hosts/tunnels'
# Will send -HUP to dnsmasq to reload hosts
# USING_DNSMASQ=1

Save above to /etc/wireguard/wg1.wstunnel and customise. Then all you have to do is sudo wg-quick up wg1. Behind the scenes wstunnel.sh will:

1. Obtain current IP of yourhost.tld

2. Update /etc/hosts with current IP of yourhost.tld

3. Add custom route to yourhost.tld via default gateway

4. Launch client side of wstunnel (as nobody)

5. Route all traffic through wireguard tunnel

6. Clean up when you are done

   sudo wg-quick down wg1
   

   • stop tunnel app
   • cleanup /etc/hosts

Limitations

Currently Wi-Fi disconnects are likely to cause non-recoverable errors and will require bringing wireguard interface down and then back up manually. This is because route to the server is set up once and is not updated as you connect to a new router with possibly different gateway.

I have only needed this on MacOS, Linux client will be very similar, but will likely need some changes here and there.

Notes on Security

It’s important to use --restrictTo=127.0.0.1:51820 option of wstunnel on the server as wstunnel is not authenticated and you don’t want to let others use your machine as a proxy. With that option “bad guys” would only be able to send UDP packets to a port that is already open anyway and will appear silent unless they have your private key.

Don’t run wstunnel as root, systemd file above launches wstunnel as nobody.

Make sure that wstunnel on a client side listens on localhost only, and doesn’t run as root.

Make sure files under /etc/wireguard/ are accessible by root only, wg-quick runs as root and so is wstunnel.sh, and it sources wg1.wstunnel as root also, so make sure they are not writable by anyone except root.

Notes on Debugging

• netstat -nr -f inet display routing table for ipv4

• Use

  nc
  

  (netcat) for testing UDP tunnel

  • server nc -u -l 51820 (stop wireguard first)
  • client nc -u 127.0.0.1 51820

• Check your public ip: curl http://api.ipify.org/

• If using nginx view logs: sudo tail -f /var/log/nginx/access.log

• Change -q to -v on the server, then sudo journalctl -fu wstunnel

• wg-quick is just a bash script