Citation needed.
> "It is best for users to know that their system is vulnerable, and how to fix that without waiting for a system update."
Stepping outside the 'tech' social bubble, most general users likely won't create a root account and password from something they see on TV or their local news site or at least not before a patch would have been released.
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Further to previously provided examples:
https://www.cloudflare.com/disclosure/
https://access.redhat.com/security/team/contact
https://www.xenproject.org/security-policy.html
https://about.gitlab.com/disclosure/
https://help.github.com/articles/responsible-disclosure-of-s...
https://www.kernel.org/doc/html/v4.10/admin-guide/security-b...
https://www.drupal.org/drupal-security-team/general-informat...
https://www.cisco.com/c/en/us/about/security-center/security...
https://www.juniper.net/us/en/security/report-vulnerability/