Brave leaking DNS servers

[Gaud]

Description of the issue:
Brave is leaking router DNS when Secure DNS is configured to use another DNS and when a VPN is extension is used. The same problem happens when Windows network adapter was configured with another DNS.

How can this issue be reproduced?

1. Set secure DNS with any provider (exemple used here: clouflare)

2. Visit http://www.whatsmydnsserver.com/ or https://browserleaks.com/ip
3. Check DNS servers
4. Cloudflare DNS appears along with my router DNS.

or

1. Activate a VPN extension (example used here: Windscribe but i tested with Avira Phanton too)

2. Visit http://www.whatsmydnsserver.com/ or https://browserleaks.com/ip
3. Check DNS servers
4. The VPN provider DNS appears along with my router DNS and the secure DNS config from above (Cloudflare).

Expected result:
The DNS tests should show only the private DNS or the VPN provider DNS in each situation.

Brave Version( check About Brave):

Version 1.18.77 Chromium: 87.0.4280.101 (Official Build) (64-bit)

Additional Information:

1)When VPN is used through a desktop app (and not an extension), the DNS is not leaked.

2. The same tests were repeated with Chrome and Edge, and none have leaked router DNS or the private DNS when VPN extension was active.

[gmacar]

@Gaud

1. Set secure DNS with any provider (exemple used here: clouflare)

2. Visit http://www.whatsmydnsserver.com/ or https://browserleaks.com/ip
3. Check DNS servers
4. Cloudflare DNS appears along with my router DNS.

Does Chrome have the same bug? It might depend on Chromium.

[SamGreenwood]

You could also run Cloudflare Warp on your computer so you have the Cloudflare DNS for the entire computer.

[Gaud]

No, Chromium browser doesn’t leak DNS. I tested Edge, Chrome and Firefox and they are not leaking anything. I reinstalled and restored Brave default configs too, and Brave still leaks DNS

[Gaud]

I’m actually using NextDNS and not Cloudflare. Anyway, Brave should notleaks dns when using any VPN…

[gmacar]

@Gaud

No, Chromium browser doesn’t leak DNS. I tested Edge, Chrome and Firefox and they are not leaking anything. I reinstalled and restored Brave default configs too, and Brave still leaks DNS

I guess you should report the bug on GitHub then: https://github.com/brave/brave-browser/issues

[gmacar]

@Gaud

1. Set secure DNS with any provider (exemple used here: clouflare)

@Gaud I’ve got an idea. Since you use Cloudflare, let’s check: open https://1.1.1.1/help and then copy-paste the (long) URL under “Please include this URL when you create a post in the community forum.”

[Gaud]

I did a similar test using NEXTDNS.

The user can check if everything is correct by entering #NextDNS. It shows an advise if you correctly configured when using NextDNS servers (or not). With NEXTDNS DoH configured through private DNS, the advise kept changing between “correct” and “wrong”. Add to that, it also pointed my router DNS when advise me about wrong configs. It only happens with Brave too.