Various Yii 3.0 related documentation
Security issues are typically sent via a security form.
If an issue is reported directly to a public page such as repository issue or a forum topic, get the message and delete the issue. Say thanks to the reporter and point to the security form for next time.
Verify that the issue is valid. Request more information if needed.
Create draft GitHub security advisory.
Ask reporter if he wants a credit for finding the issue. If so, point to his GitHub account.
When you’re ready, request a CVE.
Prepare a pull request fixing the issue. GitHub allows doing it in a private fork.
It usually takes several days.