wp-boxer-pro hack

I don’t have this plugin installed but I get a lot of traffic like:

GET /wp-content/themes/materialize/media/_frontend/css/header.css?ver=0.0.16 HTTP/1.1″ 200 1759 “https://www.example.com/wp-content/plugins/codecanyon-1497329-wp-boxer-pro/framework/admin/slider.php”

GET /wp-content/plugins/codecanyon-1497329-wp-boxer-pro/framework/admin/slider.php HTTP/1.1″ 404 35693

is it a known vulnerability that hackers try to access?