HEADS UP: Be aware of Trusted Recursive Resolver (TRR) in Firefox

tman222

I have a few Linux systems that use the ESR version of Firefox (60.x). On those systems the default setting is 0 and setting it to 5 appears to break DNS altogether. So I'm guessing 5 is not a supported option on the ESR version. Checking out a more recent version of Firefox on a couple Mac's did allow me to set the option to 5 and everything still works.

Some more info about disabling DoH from Mozilla:

https://support.mozilla.org/en-US/kb/configuring-networks-disable-dns-over-https

Glad that Pi-hole is already had a PR on this.

@johnpoz - can you explain what "local-zone: "use-application-dns.net" static" does exactly and how in NXDOMAIN being returned? Thanks in advance.

johnpoz

So per their disable article you linked to, if that domain returns a NX vs actual IP then firefox is not suppose to use doh..

So if you set that in your options box.
server:
local-zone: "use-application-dns.net" static

When a query is done for that - it will return NX.

$ dig @192.168.9.253 use-application-dns.net

; <<>> DiG 9.14.4 <<>> @192.168.9.253 use-application-dns.net
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 23041
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;use-application-dns.net.       IN      A

;; Query time: 0 msec
;; SERVER: 192.168.9.253#53(192.168.9.253)
;; WHEN: Sun Sep 08 14:22:35 Central Daylight Time 2019
;; MSG SIZE  rcvd: 52

Notice the
status: NXDOMAIN

I have sent a PM to bbcan177, but haven't heard anything back yet... But yeah would be nice if pfsense works out something - say if pfblocker is being used, unbound will auto return the NX for that, or something..

Or maybe pfsense could put in a check box to have that return NX..

I really don't now what Mozilla is thinking here.. That is great you want to offer this for your clients - but it really should be OPT IN ONLY!!! Run a PR campaign to get your users to set it.. but making it default is WRONG..

I have set the network.trr to 5 again, will keep an eye on that, and have set
security.enterprise_roots.enabled
To true as well.. so will be watching that as well, when the next update comes out.. Running 69.0 currently of firefox.

tman222

@johnpoz said in HEADS UP: Be aware of Trusted Recursive Resolver (TRR) in Firefox:

local-zone: "use-application-dns.net" static

Thanks @johnpoz - I appreciate the follow up an explanation. I was actually more curious what that configuration line did exactly and why you chose it specifically to solve this issue?

Is the idea just to create a local DNS Zone with this domain, but since no actual (local) records exist for it, it will simple return NXDOMAIN?

Thanks again!

johnpoz

Exactly, when you set the local zone as static, and no local entries - NX gets returned. So when NX gets returned when the browser looks for that, it is suppose to not enable DOH because local filtering is in place and the user has opted to use that vs doh.

edit: I can foresee future posts about why pfblocker is not working because browser is using doh vs asking the local dns which is using pfblocker.

tman222

Thanks @johnpoz - when entering into Unbound's option box, for multiple configuration options, is the correct syntax:

server:
config line 1
config line 2

OR

server:
config line 1

server:
config line 2

Apologies, I can never quite remember. Thanks again for your help.

kiokoman

bind9 + rpz
cloudflare-dns.com IN CNAME .

johnpoz

You only need 1 server: at the top

For example here are all my entries.
server:
private-domain: "plex.direct"
local-zone: "use-application-dns.net" static
so-reuseport: no
#log-queries: yes
#log-replies: yes
#private-address: ::/0 # filters out all AAAA !

I leave the log entries in there and the private address thing to stop AAAA because I enable them on the fly sometimes for testing.. I just leave them # out normally when I don't need them. I think I can remove that so-reuseport: no since I think that was changed in an update a while back.. Not sure on that one. But yeah you only need the one server: entry.

pfSenseTest

@johnpoz said in HEADS UP: Be aware of Trusted Recursive Resolver (TRR) in Firefox:

I think I can remove that so-reuseport: no since I think that was changed in an update a while back.. Not sure on that one.

I was wondering about this myself and haven't been able to confirm if it is still needed or not.

johnpoz

@johnpoz said in HEADS UP: Be aware of Trusted Recursive Resolver (TRR) in Firefox:

so-reuseport: no

I just commented it out and restarted unbound, and there are still multiple threads.. So its no longer needed..
https://forum.netgate.com/post/809158

JimP goes over in that post

JeGr

The whole use case Mozilla and the DoH folks that promote it that much are telling is falling apart IMHO. If a simple NXDOMAIN for the use-application-dns.net Zone is "blocking" the use of DoH in Firefox alltogether, how in the hell is the DoH implementation in Firefox well-thought in the first place? They are pointing fingers at MITM or Rogue ISPs etc. to protect your data and privacy against. OK, fair point, but how in the hell is that protecting if you

completely screw up a fine configured local DNS resolver setup with internal domains by using a DoH server from an external source (and handing your DNS data to them!?)
can override your privacy-DoH-firefox-thingy by said rogue ISP to simply hand out a nxdomain for the use-application-dns.net zone?
begin to segregate DNS into "per application use"? Firefox using DoH with Cloudflare, System using local resolver with internal domains, next Browser/Application uses whatever the f*** they want? How is that transparent and protecting anything about your privacy if you don't have a clue anymore what your system does? It's something like the whole Linux-systemd-everything. NTP? DNS resolving? Yay let's put it into systemd, too! What!?

Narf

kiokoman

simple. privacy is a businness after all. it will not be strange if that work was sponsorized by cloudflare and the like. they are only selling all your data to them and telling you that this way you are more protected
i hate when company make fun of customers. if they left it as an option instead of imposing it as a default it would have been something else

johnpoz

Now it seems google/chrome wants to join in on the data mining fun.. WTF!!!
https://www.zdnet.com/article/google-to-run-dns-over-https-doh-experiment-in-chrome/

dot is easy to block since uses its own port... But guess its time to start compiling list of all known doh servers and blocking them.. Gawd Damn it!!!

JeGr

@johnpoz said in HEADS UP: Be aware of Trusted Recursive Resolver (TRR) in Firefox:

But guess its time to start compiling list of all known doh servers and blocking them.. Gawd Damn it!!!

They are also contradicting their own argumentation. Mozilla for example arguments over governmental or rogue ISPs grabbing your data. At the same time they 1) send all your data to a single provider instead of using resolvers to dsitribute the DNS calls to a wide range of servers and 2) use use-application-dns.net as their canary to determine wether or not to disable automagic DoH. So we roll out some application specific black magic BS that breaks your local setup but hand out the free pass for their own attackers to disable it. WTF? How is that thought-out? First thing a rogue ISP or anyone else would be to hand out NXDOMAIN to use-application-dns.net calls to disable that. And if anyone does that... yeah.

Pushing OS developers to include DoT and DoH in their base OS and as next step push all DNS servers to wide-range adaption of both protocols would be the right way. Then you could just tell your local resolver to use either DoH/DoT for resolving (and do or don't fallback to normal udp/53 DNS). Their tactic? No just send it all to Google/Cloudflare etc. Right...

kiokoman

the Internet Services Providers Association (ISPAUK), a trade association for internet service providers in the UK, decided to nominate Mozilla for its award of 2019 Internet Villain, next to Donald Trump and the EU's Article 13 Copyright Directive.

https://www.zdnet.com/article/mozilla-no-plans-to-enable-dns-over-https-by-default-in-the-uk/

https://www.ispreview.co.uk/index.php/2019/07/ispa-pulls-uk-internet-villain-category-over-mozilla-doh-fallout.html

ISPAUK have a point here

An application switching to DoH should ensure that this switch does not undermine choices that have been previously made by the user. For example, if parents have decided to filter an internet connection in their home via network or local level DNS controls, these choices should not simply be ignored by the application.

If DoH doesn’t work or is slow, a customer’s internet access will be affected. The customer will contact their ISP, not the DoH provider, but the ISP won’t be able to fix things for them. As a minimum, any application switching to DoH should ensure that the selected resolver should provide a 24/7 user call centre reachable via low-cost/local rate telephony and an online support capability. Support for fault-diagnosis and resolution between ISP, resolver and users should also be provided.

johnpoz

@kiokoman said in HEADS UP: Be aware of Trusted Recursive Resolver (TRR) in Firefox:

An application switching to DoH should ensure that this switch does not undermine choices that have been previously made by the user

All of which just SCREAMS this can not be opt-out, but MUST be OPT-IN to switch...Where the users has to specifically do something to actually use it, vs just using the OS already set dns..

edit:
I think the thought process has gone something like this.
Q: How can we mine more data from our users without logging and sending the info where they go.. "telemetry" they don't seem to like that.

A: Lets have them use us for dns, so that we know everywhere they they go.

Q: How can we get them to do that?
A: We will tell them its for their own security, from the bad isp they are paying every month for internet.

Q: Well they are not switching over fast enough, and we don't want to actually spend any money on PR to have them think this is best option for their "security/privacy"

A: Lets just switch them over, and state that is for their own good if they complain, because they are just too stupid anyway.

bcruze

https://apple.news/AREysIdXnROWCIANTguz06A

Not sure if the link will work, they are trying a personal vpn now..

johnpoz

They can offer whatever they want - just don't freaking make something like that default... If the user has to turn it on, and make an effort to use it..

johnpoz

So I found this listing of known doh servers
https://github.com/curl/curl/wiki/DNS-over-HTTPS#publicly-available-servers

I have a pm out of @BBcan177 asking if he plans on easy way of blocking these in pfblocker, if not will be working my own listing of them to use in firewall rules and host overrides to block queries for them.

Will prob have dns queries for their fqdn point to a specific IP that I block and log, and any hits to that rule get attention and any devices doing it will if not easy to disable be off the network..

JeGr

I'd also use

local-zone: "use-application-dns.net" static

in the DNS Resolver "custom options" box so to answer with an NXDOMAIN to the canary domain Mozilla uses. Won't help if they switch their approach or simply use a service manually entered but at least the "automagic switch" should be off then.

johnpoz

Yeah been in place for some time already ;)

Notice I posted how to do it like 8 days ago ;) Look back over the thread..