My coworkers recently tried a new New York-based food delivery startup and found that their auth wasn't even HTTPS. Forget XSS or SQLI, this is basically propping your front door wide open with a sign "please take whatever you want".
Worst part is when we emailed them they tried defending the use of HTTP for auth. Took a bit of convincing to get them to take us seriously.
There are a lot of startups out there whose security practices aren't just deficient, they're straight up amateur hour.