Defence against the DoH! Arts

I’m afraid it’s another post about DNS-over-HTTPS, but there’s a lot going on. Whilst the current crop of DoH servers don’t suffer from the same problems as normal open DNS resolvers, they do have issues of their own. Whilst fans of DoH are right when they that nothing stopped applications from doing their own DNS before and that the bad guys have always tunnelled data over other protocols. It is also true that DoH has massively lowered the bar for them both in terms of readily available libraries and in the provision of vast, highly resilient, free, tunnelling infrastructure provisioned by reputable companies. However I don’t want to get back into that again, instead lets review the latest happenings in the world of Doh. In the last month we’ve had : a DoH controlled spam campaign, the first malware to leverage DoH and Mozilla nominated for Internet villain of the… Continue reading

DoH no!

As was entirely predictable DNS-over-HTTPS has now been implicated in a spam campaign. Google DoH instance was used to access TXT records to control the spam campaign via a bit of javascript on web pages. This isn’t a weakness in DNS or for that matter in DoH, it’s just using Googles DoH as a side channel. They could have achieved the same thing by accessing a specific web page, but that would be more easily blocked or shut down. There are also mobile application, both IOS and android, that are using DoH by default without giving the user a choice in the matter*. At this point if you use DNS as part of your security posture – either via RPZ, pi-hole or some other mechanism ( and if you aren’t you really should ) then you need to be blocking DoH. At present there are over 70 advertised public DoH… Continue reading

RPZs a personal history

Ten years ago today at a “secure off site meeting” ( i.e. in the pub ) I asked a colleague if there was any reason why we couldn’t use DNS load balancers to “load balance” bad domains to an address of our choosing. After some thought there didn’t seem to be any reason why we couldn’t do it or why it wouldn’t work. So the next morning as it still seemed like a good idea we added load balancing rules for three choice domains with less than savoury reputation. This quickly proved to be quite a successful tactic so we dubbed it “the naughty step”, and assumed that as it was such an “obvious” thing to do loads of other people must also be doing it. After we’d been going on like this for a while Paul Vixie published his excellent article on taking back DNS, which gave us a… Continue reading