Simple AD Cyber Security Lab (Part 3) - OPNSense Gateway

In the pervious part we installed VirtualBox and prepared to start installing our VMs.  In this part we will finish the networking part of the lab setup.

    As we get started with building our lab we have some plumbing we should take care of.  With the gateway, we will be able to allow our lab access to the Internet but prevent it from accessing our home network.  This is important as it will allow us to do updates and install applications while protecting our home network from unintended targeting by any tools we run in our lab.

Warning:  This is in no way a best practices guide and should not be used for the installation of a production or even home firewall.

Create VM

First, let's Download and extract the installer for OPNSense

Download from https://opnsense.org/download/ we want the "amd64" and "dvd" options

Once downloaded right click select 7-Zip and Extract here

Open up VirtualBox select Machine and New

Set our Name and Operating system

• Name: GW - OPNSense
• Folder: This should be the default location we set in part 2, only change this if you need to store your VM's in different locations
• ISO Image: select the installer we extracted
• Type: BSD
• Subtype: FreeBSD(this is what OPNSense runs  under the hood)

Next let's go to hardware, I know this is not what is on the plan from part 1.  The installer can fail with less then 3GB of ram and the extra CPU just makes the install much faster.  We will turn these back down after the install is complete.

• Base Memory: 3096 MB
• Processors: 2

Lastly, let's go to Hard Disk set our size and Finish

• Hard Disk File location and Size:  Size to 16.00 GB (even if you have extra space no need to go larger here)

Now we have our VM but we still need to tweak our network interfaces.  By default, we only get one and it is not set the way we want it

Select our VM and click on the settings gear

Go down to Network and change Adapter 1 to bridged, the Name should be the host's active network adaptor, in my case that is the built in WiFi.  This will be our WAN/Internet interface.  

Take note of the MAC Address listed we will want that in a later step

On the Adaptor 2 tab we will set up our LAN/lab interface, then click OK.

• Enable Network Adaptor: check
• Attached to: Host-only Adaptor
• Name: VirtualBox Host-Only Ethernet Adaptor #2 ( the one we created in part 2)

We are now done with the initial setup of the VM and ready to install OPNSense

Install OPNSense

With our GW VM selected click on the start arrow, you can also use the detached mode from the down arrow on the start button to get a larger separate window.

This will boot up the live disk it may take a while

Once we get to the login prompt we will log in with the user "installer" and password "opnsense" to begin the install

• User: installer
• Password: opnsense

Select your keyboard layout using the arrow keys and the spacebar then Select

Take the default Install (ZFS) and OK

You should only see this if you selected less than 3 GB of ram, from my experience the installer will fail if you continue.  Power off the VM and adjust the ram under the settings menu

We have one drive and don't need redundancy for this lab so select stripe

Select your drive with the spacebar then OK

Yes, we really want to destroy our virtual drive, as long as you have the VirtualBox menu and icons here you are safe to proceed, the disk listed is a file on your host's storage so this will not hurt your host ssytem

Now we wait while the installer runs, if you added that second CPU just imagine how slow this would be with out it.  If you didn't add it, you might want to find something to do for a while...

And the install is finally done, let's set a root password

Type in then confirm your password

Complete Install

Select Halt now, this will power off our VM so we can go in an update the hardware

Back in the settings under System then Motherboard set our ran to 512 MB

• Base Memory: 512 MB

On the Processor tab we can go back to 1,  If you have extra CPU you can leave this but this VM really won't need more than 1

• Processors: 1

Under Storage let's remove our install media, select the DVD ISO and Remove Attachment

Yes, we want to remove the optical drive, it is unneeded past the installer

Now we have OPNSense fully installed we can move on to configuring it.

Configure OPNSense

Let's start our VM back up and login with root and the password we created

First, we need to assign our interfaces, OPNSense will take a guess at it but is not always correct.

Enter 1 to assign interfaces

No LAGGs or VLANs needed for our lab setup

Okay for our WAN interface, this will be Adaptor 1 in our VM, if you noted the MAC address from before you can use it to select the correct interface.  You can also go into the VM settings and look if needed.   Type in the name em0/em1 of the matching interface and hit enter

We will then enter the other interface for our LAN then just hit enter for Optional Interface 1 as we only have 2 interfaces.  If your WAN and LAN interface selection looks correct Y to proceed

Back at the main menu, type in 2 to set our IP addresses

We only need to configure our LAN interface it should be option 1

• LAN IPv4 address: 172.16.254.1
• Subnet Mask: 24

Select No(n) the rest of the way through the interface config

Now OPNSense is installed and configured.  One last set to go.

Create Rule

    Now for the reason, we are using a firewall and not just a router.  Let's create a rule that will prevent our lab from talking to any private networks our host computer happens to be connected to.

From your host computer, you should be able to browse to https://172.16.254.1, here we should find the web gui for OPNSense login with root and the password you created.

Now go to the Firewall menu and Aliases, click on the Add button

Let's create the following Alias and save

• Name: RFC1918_Addresses
• Type: Network(s)
• Content: 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16
• Description: Private address blocks

After saving we need to Apply our changes

On to the Rules then WAN menu still under Firewall and select Add

Here we will create the rule using our Alias then save at the bottom

• Action: Block
• Direction: out
• Destination: RFC1918_Addresses

After saving we need to Apply changes

This rule will take a few seconds to apply but will prevent our lab from being able to communicate with the private IPv4 networks that are used for both home and business networks.  

Now that our plumbing is finished we will move on to getting Active Directory setup in the next part.

OPNSense force DNS over TLS network wide

 DNS is a critical service for the Internet.  Not only every webpage you visit but even much of the content on each website requires a DNS lookup to find the server where the content is located.  DNS by default is also not encrypted, allowing anyone in your traffic path such as your ISP to see every web page you visit even if you are not using their DNS servers.  Because of this, it has become one way of tracking people online.  We do have a few options to at least cut our ISP off from some of our data.  We could use a VPN but they are not always ideal.  So today I am going to focus on DNS over TLS.  TLS(Transport Layer Security) is the same encryption used to protect websites and also allows us to verify that the server we are talking to is who we think it is.

 

 

Using OPNSense, we need to do only a few things to protect our entire network.  Let’s get started!

 

• Enable DNS over TLS
• Prevent DNS leakage
• Test

 

Enable DNS over TLS

 

For this, we will be using Unbound DNS, which should be installed by default on OPNSense.  If you have any other DNS servers enabled on OPNSense, you must turn them off.

 

Open up the Services Menu

 

 

Then open Unbound DNS.

 

On the general tab check to enable Unbound, make sure the port is 53 and you have the network interfaces you host DNS on selected.  By default, this is just LAN.

 

 

On the Query Forwarding tab we want to make sure “Use System Nameservers” is disabled.  This setting will prevent the use of DNS over TLS.

 

On the DNS over TLS tab, we want to make sure “Use System Nameservers” is disabled.  This setting will prevent the use of DNS over TLS.  The new will add the name servers we want to use.  I’ll use Cloudflare in this example but feel free to use your preferred DNS service.

 

 

Add server, for Cloudflare the servers are 1.1.1.1 and 1.0.0.1 on port 853.  The CN(Common Name) is used to verify the TLS certificate, so we can be sure we're talking to Cloudflare.

 

 

Once our servers are added click apply.

 

Now all the DNS requests that come into OPNSense should be forwarded to the name servers we defined over TLS!  Note, that the DNS requests made by OPNSense itself won’t use TLS when it reaches out for things like updates.

 

 

 

Prevent DNS leakage

Unfortunately, not everything will honor the DNS settings we provide from our DHCP.  Smart home and IoT devices are notorious for preferring their own DNS settings.  While we can’t configure them directly, we can block them from reaching out on their own so they have to use our DNS.  Let’s put in a firewall rule to block all outbound DNS traffic over port 53(the default unencrypted DNS port).

 

For this, we will be under the Firewall menu.

 

Go to Rules

 

We are looking for DNS traffic destined for the Internet so we will put the rule on the WAN interface.

 

 

Click on the button to add a rule.

 

The Action should be “Reject”

Quick “Apply the action immediately on match” this will stop further processing of firewall rules once this rule is matched.

The interface should be WAN.

Direction Out

 

Destination port range from any to (other) port 53

 

Let’s also enable logging so we can verify, feel free to disable this later as it may generate a lot of logging in your environment.

 

Save our rule

 

It should look like this on the rules list.

 

Apply our new rule

Now we have enabled our firewall to receive plain unencrypted DNS requests on our network and forward them out over TLS and have a firewall rule to prevent devices from bypassing our DNS settings and going out unencrypted.

Test

So we implemented all this stuff but is it working?  Let’s find out.

 

From your browser, you can use the below site to verify your browser is using the DNS servers you specified.  In this example, Cloudflare’s DNS servers 1.1.1.1 and 1.0.0.1 are load-balanced IP addresses.  Each of them has many DNS servers behind them all over the world.  Our responses won’t be from  1.1.1.1 or 1.0.0.1 but they should be from Cloudflare and the Country should be in your region.  I’m in the southwestern US so this looks good.
https://www.dnsleaktest.com/

 

It is good to see our computers are using the correct setting but what about the other pesky devices on our network?  Let’s see how our firewall rule is doing.

Back under the Firewall, we can look at the logging we enabled

 

Select Live View.

 

Let’s put in some filters so we can see what is happening to DNS traffic trying to bypass our settings.

 

Destination port(dst_port) is 53(the default DNS port for nonencrypted DNS)

 

The interface is wan, this will show us just what is going out to the Internet, you may also see inbound DNS attempts from the Internet this is why we have firewalls……

I have one other rule just to prevent my current public IP from being listed.

 

You may see a sea of red as I do, smart home devices sure are uh fun….  If you see devices reaching out and getting a pass(green) you may need to look at if you have other firewall rules allowing the traffic.

 

Now our ISP can no longer see all of our DNS traffic!

 

One thing we didn’t do is block DNS over TLS to providers other than the one we set up. Some browsers use their DNS over TLS to “Protect” the user or so they get your tracking information depending on how you look at it.