A Cross-Site Scripting (XSS) issue was discovered in webpagetest 3.0. The vulnerability exists due to insufficient filtration of user-supplied data (bgcolor) passed to the webpagetest-master/www/video/view.php URL. An attacker could execute arbitrary HTML and script code in a browser in the context of the vulnerable website.
https://github.com/WPO-Foundation/webpagetest/issues/837
https://github.com/MarkLee131/awesome-web-pocs/blob/main/CVE-2017-6537.md