If it’s not publicly known and is a security risk it is far more effective to directly contact the developers / companies security team so they can immediately work on actually protecting people by developing a patch. If they don’t respond quickly (subjective, I’d call it within 12 hours) or fail to issue a fix in a timely manor (subjective, I’d say 24 hours) then yes - go public, start by logging a bug report and link to that bug report or if you can’t - the bug number / reference.