uBlockO causing some sort of DNS leak

[Kraxys]

Prerequisites

• [x ] I verified that this is not a filter issue
  • Filter issues MUST be reported at filter issue tracker
• [ x] This is not a support issue or a question
  • Support issues and questions are handled at /r/uBlockOrigin
• [x ] I performed a cursory search of the issue tracker to avoid opening a duplicate issue
  • Your issue may already be reported
• [x ] The issue is not present after wholly disabling uBlock Origin ("uBO") in the browser
  • If the issue is still present after wholly disabling uBO in the browser, then the issue is unrelated to uBO
• I tried to reproduce the issue when...
  • uBO is the only extension
  • [x ] uBO with default lists/settings
  • using a new, unmodified browser profile
• I checked the documentation to understand that the issue I report is not a normal behavior

Description

On a clean and fresh Portable FF I have installed 2 extensions: FoxyProxy Standart and uBlock0. No hack performed on ublocko. With FoxyProxy, I set up a socks5 proxy connection, say with a proxy in the US. My ISP is in Spain. I triple-check that in FoxyProxy UI, Send DNS through SOCKS5 proxy is green. Moreover, in about:config, network‧proxy‧socks_remote_dns is true.

1. When uBlockO is wholly disabled (or uninstalled) DNS-leaktest sites such as https://www.perfect-privacy.com/en/tests/dns-leaktest or https://www.grc.com/dns/dns.htm, only an US Dns IP is displayed, which is perfectly normal.

2. As soon as I enable uBlockO in Tools-> Addons, the same tests on the same sites are both displaying an US Dns IP and two Spanish Dns IP (precisely those of my ISP). The same issue occurs even if I deactivate uBlockO on each of the previous site.

A specific URL where the issue occurs

https://www.perfect-privacy.com/en/tests/dns-leaktest
and
https://www.grc.com/dns/dns.htm

Steps to Reproduce

1. Installing FoxyProxy and setting up a socks5 proxy with network‧proxy‧socks_remote_dns set to true
2. Testing Dns on previous sites: Only Dns relative to the proxy is displayed
3. Installing uBlock, and testing Dns again: The ISP Dns IPs are displayed along with the Dns IP relative to the proxy>.
4. Deactivating uBlock on each previous sites: Same problem.
5. Completely disabling (or uninstalling) uBlockO, and testing again on the same sites: only the Dns IP relative to the proxy is displayed.

Expected behavior:

When using a socks 5 proxy with network‧proxy‧socks_remote_dns set to true, every Dns test site should display only the Dns IP relative to the proxy.

Actual behavior:

Cf description above

Your environment

• uBlock Origin version: 1.35.2
• Browser Name and version: FF 89.01 (but same problem with previous versions)
• Operating System and version: W10 Home & Enterprise (tested on VM).

[uBlock-user]

https://github.com/gorhill/uBlock/wiki/Dashboard:-Settings#uncloak-canonical-names

Disable Uncloak canonical names in Settings

[gorhill]

Duplicate of #911.

There is now a setting to disable cname-uncloaking, you can disable it yourself as you see fit.