The remote web server is running a PHP application that is vulnerable to a cross-site scripting (XSS) attack.
Versions of MyBB (MyBulletinBoard) prior to 1.6.15 are affected by a cross-site scripting vulnerability. Specifically, the flaw affects 'video MyCode' and exists because the program does not validate input before returning it to users. This may allow a remote attacker to create a specially crafted request that would execute arbitrary script code in a user's browser session within the trust relationship between their browser and the server.
Upgrade to MyBB version 1.6.15 or later.