Stored XSS Using Media

Hi, Summary: This exploits an XSS vulnerability on polldaddy.com Steps to Reproduce: 1. Create a multiple-choice question quiz on Polldaddy 2. Insert stored XSS payload into Media Embed such that it matches the shortcode format Payload: [<img src="http://url.to.file.which/not.exist" onerror=alert("Hello!");>] 3. When someone goes on the quiz page through the quiz share link, the payload will execute. Proof of Concept (30-second video): https://drive.google.com/file/d/0B_lsH7QMy9DkQnV5a3hHa05lSmM/view