1766723 - DNS lookups in .pac proxy config don't use DNS over HTTPS

Status: RESOLVED WONTFIX

(Core :: Networking: DNS, defect)

Description

[ra_hardy]

Steps to reproduce:

1. My organisation has a proxy autoconfigured with a .pac file in Windows
2. The pac does a DNS lookup using isInNet()
3. Firefox is configured to use the system proxy stetings
4. I've selected the 'enable DNS over HTTPS' option in the settings
5. In Firefox, go to example.com
6. At a command prompt run ipconfig /displaydns

Actual results:

The DNS lookup for example.com displays in the Windows DNS cache

Expected results:

The isInNet() call should use DNS over HTTPS and not use the system DNS

It seems that when a .pac is configured and has DNS lookups in it, then the 'enable DNS over HTTPS' option essentially has no effect since the DNS lookups aren't secured.

I've tested using the .pac URL directly in Firefox instead of the 'system proxy' setting, and the result is the same.

I've also tested by breaking the .pac URL. In that case the DNS lookup is using DNS over HTTPS instead of the system DNS.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Networking: DNS' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Kershaw Chang [:kershaw]]

Please see bug 1640091.
This is an expected behavior - DNS lookups from pac cannot use DoH.

Comment 3

[ra_hardy]

As the setting for 'Enable DNS over HTTPS' setting has no effect, should it be disabled, or have a small explanation.