Is there a way to report a bug in Salesforce Trailhead. The third step of Security Superbadge definitely contains an error. When I click "Submit" button the page makes AJAX call which fails with 500 status code and "Submit" button hangs forever.
You can send a tweet to @trailhead, and they'll respond in a timely manner. They'll probably want to DM with you for more information. I recently reported a problem where the system would just hang and never validate a challenge, and they got back to me quickly.