Currently, "localhost6" and "localhost6.localdomain6" host names resolve to the IPV6 loopback address ::1 only, bypassing native DNS, and corresponding origins are treated as secured. The goal of this entry is to remove this non-standard behavior.
This will improve interoperability since there is no specification defining this behavior and no plans in WebKit/Firefox to implement it.
There is a potential risk to break websites relying on these host names. It seems this was implemented ten years ago, motivated by existing DNS resolution in some Linux distributions. Public usage seems very low : on 218315452 urls from HTTPArchives, only 1 really uses localhost6 as a URL host and only as a JS example (namely https://hello-renovation.jp/assets/js/stories_recommender.js ) that is less than 0.000000005%.
People willing to continue to treat localhost6 and localhost6.localdomain6 specially for local development or specific systems can still configure native DNS. Chromium also implements a special allow list as permitted by the specification: https://source.chromium.org/chromium/chromium/src/+/master:services/network/public/cpp/is_potentially_trustworthy.h;l=43;drc=bf799475f9ff40b7e1e2be2fd3a68911c4f047ee
This is reducing the scope of "potentially trustworthy" so making security stricter.
-- Frédéric Wang
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LGTM1. This aligns us with other vendors' behavior regarding these domain names, and removes a Chromium weirdness that was both undertested and unspecified. I don't expect it to be used at all publicly, and I don't think it's going to be possible for us to understand its usage in private networks given those networks characteristics. Since it was never supported in any non-Chromium browser, and its support in Chromium was initially predicated on its presence in specific platforms' /etc/hosts file, I expect minimal breakage. Developers can work around this removal by a) dropping the "6" from their pages (`localhost` is both interoperable and secure), b) adding `localhost6`, etc to their local /etc/hosts, or c) adding `localhost6` to their DNS resolver. Any seem workable.
Thanks Mike, just a nit: for b) or c) I think one might need to
do something to keep "localhost6" potentially trustworthy.
However, I think this option is enough:
Chromium also implements a special allow list as permitted by the specification: https://source.chromium.org/chromium/chromium/src/+/master:services/network/public/cpp/is_potentially_trustworthy.h;l=43;drc=bf799475f9ff40b7e1e2be2fd3a68911c4f047ee
-- Frédéric Wang
To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CALjhuifswRbBCFiaY%3DWZOTRAW7wtZtTYp205syjwMpk%3DdP%3Dtyg%40mail.gmail.com.