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OpenBSD firewalling Windows 10, NetBSD’s return to ptrace, TCP Alternative Backoff, the BSD Poetic license, and AsiaBSDcon 2018 videos available.

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Preventing Windows 10 and untrusted software from having full access to the internet using OpenBSD

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