DNS leaks using OpenVPN client tunnel

[strangegopher]

Do you not see this under Services/DHCP Server/LAN?

[Derelict]

That DOES NOT MEAN that you do not have static DNS servers on the client you are testing, bro.

This really is. not. that. hard.

[gschmidt]

Ok….I have created the rule =Block rule.jpg
Added the google dns servers = "DHCP Server DNS Server.jpg"
and the ExpressVPN DNS servers = Static DHCP Mapping.jpg"

dnsleaktest result= dnsleaktest.jpg

:o


[gschmidt]

I did an nslookup at the client W10 PC
Which shows the DNS server of ExpressVPN
Which I entered in the Static Mapping DNS servers in pfSense

[strangegopher]

try removing the ExpressVPN DNS servers from Static DHCP Mapping and replacing it with 8.8.8.8 and 8.8.4.4

[Derelict]

It doesn't matter where anything is configured. What are the DNS servers configured on the client. Use ipconfig /all

Hell, if you're having this much trouble, configure them statically.

[gschmidt]

ipconfig /all

I dont see static dns servers?
Only the express vpn dns servers i have specified in pfsense

[strangegopher]

my guess is expressvpn dns servers might be the issue, so try using 8.8.8.8 in windows go to Control Panel\Network and Internet\Network Connections right click your interface, select properties, double click "Internet Protocol Version 4", select "Use Following DNS server addresses" and enter 8.8.8.8 and 8.8.4.4

and run dns leak test again

[gschmidt]

@strangegopher:

try removing the ExpressVPN DNS servers from Static DHCP Mapping and replacing it with 8.8.8.8 and 8.8.4.4

Check!…Still leaking Google and openDNS servers....looks exact the same as with the NAT redirection of port 53
I just did a default pfsense 2.4.2 setup (update to 2.4.3), nothing special

[strangegopher]

Well I am out of ideas then. I don't know what could be going wrong.

[Derelict]

What matters is that they are not coming from YOU. You cannot control where the resolvers you query go to get their information. If the resolvers you query don't do what you like, use different resolvers.

[gschmidt]

@strangegopher:

Well I am out of ideas then. I don't know what could be going wrong.

Look now I have removed the DNS servers at System/General Setup
And in DNS Resolver i set (see picture)
In DHCP Server all DNS Servers are empty
Also Clients have no DNS specified
Your rule (stopped temporarily)

See dnsleaktest pic!


[gschmidt]

But with this setup, all my network clients use the EXPRESSVPN interface….so if this interface is down...no internet for all

[strangegopher]

you can try setting the outgoing interface in dns to WAN and try with dhcp settings and firewall rule again and see if that works.

[gschmidt]

@Derelict:

What matters is that they are not coming from YOU. You cannot control where the resolvers you query go to get their information. If the resolvers you query don't do what you like, use different resolvers.

….my knowledge is not that fancy of pfsense I admit...but i knew that my clients did NOT have static dns servers
On a simple modem with OPENWRT this was a piece of cake....on their forum they helped instead of shouting

[gschmidt]

@strangegopher:

you can try setting the outgoing interface in dns to WAN and try with dhcp settings and firewall rule again and see if that works.

Thanx man for your help sofar, I will try tomorrow…have to get some sleep now...ciao!

[gcu_greyarea]

In my opinion handing out DNS Servers via DHCP isn't sufficient to prevent DNS Leaks. There are Clients that will use hard coded DNS Servers. E.g. I had a Roku Player and a Fire TV that bypassed my specified DNS Server with hard coded Google DNS Servers. Perhaps even Apps installed on the FireTV may use their own DNS Server.
The only thing that worked reliably was to port forward (DNAT) DNS Requests (Dest. Port 53) to my DNS Server of Choice, which is my VPN providers own internal DNS Server. If you trust your VPN provider with your Data traffic you might as well trust them with your DNS Traffic.

My VPN Provider also has a public DNS Server which pfSense uses to resolve the VPN Servers. Once the Tunnel is up my LAN clients will send their DNS Queries through the Tunnel to the VPN providers internal DNS Server.

For Clients that do not need tunneling via VPN you can hand out DNS Servers via DHCP (e.g. Google or OpenDNS). You do not need to have a DNS Forwarder or Resolver run on your pfSense box.

@gschmitt:
In your screenshot your Windows IP Config shows a DNS Server of 85.203.37.1. That is a public DNS Server. Use this Server under pfSense General Setup.
Uncheck "Allow DNS server list to be overridden by DHCP/PPP on WAN"
Check "Do not use the DNS Forwarder/DNS Resolver as a DNS server for the firewall"

I assume you use the pfSense OpenVPN Client to connect to Express VPN. Express VPN will assign you an RFC1918 Address (an internal IP Address) . E.g.

10.8.0.5 with a Gateway of 10.8.0.1

My VPN Provider (Mullvad) also has a DNS Server listening on 10.8.0.1.

So the DNAT(Port Forward rule) should forward DNS Traffic to 10.8.0.1 and there shouldn't be any leaks anymore.

[gschmidt]

Thanx for the effort man!

"I assume you use the pfSense OpenVPN Client to connect to Express VPN"

Yes

In your screenshot your Windows IP Config shows a DNS Server of 85.203.37.1. That is a public DNS Server.

Aha…I used the "public DNS Server: 85.203.37.1" for port forwarding the DNS server 53
85.203.37.1 and 85.203.37.2 are the DNS servers ExpressVPN is showing on their site.
In my pfsense dashboard I also see at the EXPRESSVPN Gateway a internal ip-address 10.111.0.21 and a remote/virtual ip-adress of 10.111.0.22
Which one should I use to DNAT port forward?

Use this (85.203.37.1) Server under pfSense General Setup

Both 85.203.37.1 and 85.203.37.2? With or without selected EPRESSVPN gateway?
Any other DNS Servers here?

Should I set DNS Servers at my DHCP Server/LAN? (for clients not going trough the VPN tunnel)
I have made static mappings for the client(s) that I want to go through EXPRESSVPN gateway.
And a firewall alias of those clients

Any special settings for System/AdvancedFirewall & NAT/Network Address Translation?
I currently have "Pure NAT"and the rest is unchecked

Greetzzz


[strangegopher]

@gcu_greyarea:

In my opinion handing out DNS Servers via DHCP isn't sufficient to prevent DNS Leaks. There are Clients that will use hard coded DNS Servers. E.g. I had a Roku Player and a Fire TV that bypassed my specified DNS Server with hard coded Google DNS Servers. Perhaps even Apps installed on the FireTV may use their own DNS Server.

I have a chromecast that uses hardcoded google dns servers primarily for geo blocking netflix, hulu, etc.

I am not sure how it works but technically even if client is using its own dns server, it shouldn't leak the real IP address.

edit: I use a vpn server in the same city as me, for speed and reliability, so geo blocking is not a concern for me.

[gschmidt]

Express VPN will assign you an RFC1918 Address (an internal IP Address) . E.g. 10.8.0.5 with a Gateway of 10.8.0.1

My VPN Provider (Mullvad) also has a DNS Server listening on 10.8.0.1.

So the DNAT(Port Forward rule) should forward DNS Traffic to 10.8.0.1 and there shouldn't be any leaks anymore.

I have difficulties finding the RFC1918 Address of the expressvpn gateway…
When i use the internal ip-adress I thought was the gateway (see previous attachment), the clients that have to go through the expressvpn tunnel have no internet connection.

Besides that, every time I reboot pfsense or restart the OpenVPN (ExpressVPN) service I get different RFC1918 Addresses.
Is this pfsense or expressvpn responible for the change?