uBO is leaking DNS (c name uncloak) again

[ThurahT]

Prerequisites

• [✅] I verified that this is not a filter issue
  • Filter issues MUST be reported at filter issue tracker
• [✅] This is not a support issue or a question
  • Support issues and questions are handled at /r/uBlockOrigin
• [✅] I performed a cursory search of the issue tracker to avoid opening a duplicate issue
  • Your issue may already be reported.
• I tried to reproduce the issue when...
  • uBlock Origin is the only extension
  • uBlock Origin with default lists/settings
  • using a new, unmodified browser profile
• [✅] I am running the latest version of uBlock Origin
• [✅] I checked the documentation to understand that the issue I report is not a normal behavior

Description

uBO is leaking DNS (c name uncloak) again

A specific URL where the issue occurs

https://old.reddit.com/ https://browserleaks.com/dns

Steps to Reproduce

1. setup proxy (polipo/privoxy/tinyproxy) and config it to not do own DNS lookups
2. control proxy settings in uBO and FF
3. realize there is DNS leakage when cname is uncloaked in uBO and browserleak page confirms it

Expected behavior:

uBO should not do DNS lookup when proxied

Actual behavior:

It does on this machine

Your environment

• uBlock Origin version: 1.30.2
• Browser Name and version: Firefox ESR 78.3.0esr (64-bit)
• Operating System and version: Devuan GNU/Linux 2.1 (ascii) x86_64 Kernel: 4.9.0-13-amd64

Pictures:
01: cname uncloak (fastly) - https://i.imgur.com/NktShRP.png
02: uBO settings - https://i.imgur.com/C1tA2Je.png
03: FF settings - https://i.imgur.com/Ci5E2MG.png
04: browserleaks show my real DNS server plus the Tor one - https://i.imgur.com/z8LRasS.png

[gorhill]

uBO just uses a browser API to resolve cname, it does not get to decide how the DNS requests are made. You will have to disable cname-uncloaking through advanced settings if you do not want this feature.

[gorhill]

Alright I will look at this when I get the time.

If you can investigate why this does not work anymore that would save me a lot of time -- I am feeling rather burdened at the moment.

[gorhill]

Did you restart uBO after you changed your proxy settings?

[gwarser]

This is fixed in Firefox 80, OP is using ESR 78

https://bugzilla.mozilla.org/show_bug.cgi?id=1618271

[gorhill]

Ok I'm hard of understanding... I will have to download 78 and test again. Also, I should fix the workaround code to execute only for versions of Firefox below 80.

[gorhill]

I tried with 78.3.1esr and I could not reproduce. This is the proxy settings I used:

[ThurahT]

Yes, I followed this issue 6 month ago with uBO 1.25.0 and the fix (1.25.x (can't remember)) solved it for ESR 68.x back then.

I tested with three different profiles yesterday and same issue on all of them (they have different privacy/security settings).

FF ESR got upgraded to 78.x last weekend or so, and I noticed this issue was back as of yesterday. It is very strange that it got introduced again. But yes. I will disable cname for now and wait for FF 80+.

[gorhill]

How do your proxy settings differ from those in my screenshot?

[ThurahT]

They're the same. Except I have mine filled with localhost and ports of course, as seen in picture 3.

[Kein]

I cant repro it, set

cnameUncloak true
cnameUncloakProxied true

Set DNS to be resolved through proxy (shadowsocks). Tested on
https://dnsleaktest.com/
and
https://browserleaks.com/dns
No leakage.

Firefox 81

[gorhill]

@Kein Well of course, the purpose of cnameUncloakProxied when set to true is to bypass the built-in protection. Leave it to false (default) if you do not want uBO to uncloak when a proxy is detected.

[Kein]

Does not make any difference for the repro case. In fact, any cname-related directives do not affect repro case and it always fails.

[Kein]

I'm not asking you to do anything, I just pointed out I cant reproduce the case OP mentioned either on FF81, that all.

[gorhill]

Duh me, I read your "I can't repro" as "I can repro". Sorry for the confusion.

[ThurahT]

Well, I am utterly confused now.. I have two other profiles (same Firefox 78.3.0 ESR) that uses the ghacks pants user.js stuff. And those do not leak DNS. But when I look at the stuff in about:config regarding proxy settings they are exactly the same as the non ghacks profile that do leak DNS and made me report this in the first place.. I do not understand it. I will wait for FF 80+ and see if they really fixed it or nah. But it seems so since people can't reproduce it. As for this issue I am fine about it being closed as can't reproduce and firefox bug. TIA for your time. And thank you for uBO.

[CyberMan571]

I cant repro it, set

cnameUncloak true
cnameUncloakProxied true

Set DNS to be resolved through proxy (shadowsocks). Tested on
https://dnsleaktest.com/
and
https://browserleaks.com/dns
No leakage.

Firefox 81

Do never forget ISP(ISS) and OS changeable!
They can send fake (request and response) data