Whilst setting up one of my development laptops to port some software to Windows I noticed Windows 10 doing crazy things like installing or updating apps and games by default after initial setup. The one I noticed in particular was Candy Crush Soda Saga which for those who don't know of it is some cheesy little puzzle game originally for consumer devices. I honestly did not want software like this near to a development machine. It has also been reported that Windows 10 now also updates core system software without notifying the user. Surely this destroys any vaguely deterministic behaviour, in my opinion making Windows 10 by default almost useless for development testbeds.
Deciding instead to start from scratch but this time to set the inbuilt Windows Firewall to be very restrictive and only allow a few select programs to communicate. In this case all I really needed to be online was Firefox, Subversion and Putty. To my amusement (and astonishment) I found out that the Windows firewall could be modified to give access very easily by programs during installation (usually because this task needs to be done with admin privileges). It also seems that Windows store Apps can change the windows firewall settings at any point. One way to get around this issue could be to install a 3rd party firewall that most software will not have knowledge about and thus not attempt to break through. However the only decent firewall I have used was Sygate Pro which unfortunately is no longer supported by recent operating systems. The last supported versions was 2003, XP and 2000. In short, I avoid 3rd party firewalls.
Instead I decided to trap Windows 10 (and all of it's rogue updaters) behind a virtual machine running OpenBSD. This effectively provided me with a full blown firewall appliance. From here I could then allow specific software I trusted through the firewall (via a proxy) in a safe, controlled and deterministic manner. For other interested developers (and security conscious users) and for my own reference, I have listed the steps taken here:
1) First and foremost disable the Windows DHCP service - this is so no IP can be obtained on any interface. This effectively stops any communication with any network on the host system. This can be done by running services.msc with admin privileges and stopping and disabling the service called DHCP Client.
2) Install or enable your favorite virtualization software - I have tested this with both VirtualBox and Hyper-V. Note that on non-server versions of Windows, in order to get Hyper-V working, your processor also needs to support SLAT which is daft so to avoid faffing about, I recommend using VirtualBox to get round this seemingly arbitrary restriction.
3) Install OpenBSD on the VM - Note, if you decide to use Hyper-V, its hardware support isn't 100% perfect to run OpenBSD and you will need to disable a couple of things in the kernel. At the initial boot prompt, run the following commands.
config -e -o /bsd /bsd
4) Add a host only virtual adapter to the VM - This is the one which we are going to connect through the VM with. Look at the IP that VirtualBox assigns this in network manager on the host machine. Mine was [b]192.168.56.1[/b]. Set up the adapter in the OpenBSD VM to have a static address on the same subnet. For example [b]192.168.56.2[/b]. If you are using Hyper-V and OpenBSD, make sure you add a "Legacy Interface" because no guest additions are available. Then set up a virtual switch which is host only.
5) Add a bridged adapter to the VM - then assign it to whichever interface you wanted to connect to the external network with. Note that if using Wireless, set the bridged adapters MAC address to the same as your physical device or the access point will reject it. This is not needed (or possible) on Hyper-V because the actual device is "shared" rather than bridged so the same MAC address is used. Again, if you use Hyper-V, then add another virtual switch and attach it to your chosen external interface. VMs in Hyper-V "share" an adapter within a virtual switch and there is the option to also disable the hosts ability to use this interface at the same time which is fine for an additional level of security if those pesky rogue apps and updaters can also enable / disable DHCP service one day which wouldn't be too surprising.
6) Connect to your network in the host OS - In case of Wireless, select the correct network from the list and type in a password if needed. Windows will probably say "no internet available", it also does not assign an IP address which is fine.
7) Install the Squid proxy package on the OpenBSD guest and enable the daemon
# pkg_add squid
# echo 'squid_flags=""' >> /etc/rc.conf.local
# /etc/rc.d/squid start
We will use this service for a limited selection of "safe and trusted" programs to connect to the outside world from within the Windows 10 host. You can also use putty on the host to connect to the VM via SSH and create a SOCKS proxy which software like Firefox can also use to connect externally.
8) Configure the software you want to be able to access the external network with
- Firefox - go to the connection settings and specify the VMs IP address for the proxy.
- Subversion - modify the %HOME%\AppData\Roaming\Subversion\servers file and change the HTTP proxy field to the VMs IP. This is important to communicate with GitHub via https:// (Yes, GitHub also supports Subversion). For svn:// addresses you can use Putty to port forward.
- Chromium/Chrome - unfortunately uses the global Windows proxy settings which defeats much of the purpose of this exercise if we were going to allow *all* of Windows access to the internet via the proxy. It would become mayhem again. However we can still use Putty to create a SOCKS proxy and then launch the browser with the following flags:
--proxy-server="socks5://<VM IP>:<SOCKS PORT>"
--host-resolver-rules="MAP * 0.0.0.0 , EXCLUDE <VM IP>"
9) Congratulations, you are now done - Admittedly this process can be a bit fiddly to set up but it completely prevents Windows 10 from making a complete mess. This solution is probably also useful for those who like privacy or don't like the idea of their software "phoning home". Hope you find this useful and if you have any issues, please feel free to leave questions in the comments.