Glossary
DNS leak
When the domain lookups of a browser behind a proxy go to the user's own DNS server, usually the home internet provider's, instead of through the proxy. A test page can then see a resolver that doesn't match the proxy's location.
Also called: DNS leak test.
A DNS leak test makes the browser look up random domain names and records which DNS servers ask for them. BrowserLeaks' test resolves 50 names and warns that faulty VPN or proxy software "can lead to your device sending DNS requests directly to your ISP's server."
With the right proxy type, Chrome doesn't do the lookup itself. Chromium's documentation says that with an HTTP proxy "name resolution is always deferred to the proxy" and with SOCKS5 it is "always done proxy side," while with SOCKS4 it happens on your device. Antidetects such as Dolphin{anty}, Octo Browser and Kameleo send DNS through the proxy by default.
A public resolver in another country isn't a leak by itself, because big public DNS services often answer from a different country than your IP. What gives you away is your home provider's resolver next to a proxy IP somewhere else.
Related terms: WebRTC leak, Proxy, Residential proxy, Browser profile.