To report Youtube security bug I found security vulnerability/bug on YouTube. I want to report. How can I report it? Is there a quick way?
Being that YouTube is a product of Google, You can report the bug on Google's report security bug, page 

From the page:


  If you have found a security bug in a Google product and want to
  report it to us, you've come to the right place. Please fill out the
  following form and we'll be in touch shortly. If this is a valid
  vulnerability report, it might also be eligible for a reward as part
  of our Vulnerability Reward Program. Thanks!