HTML attributes when attaching a YouTube link to the post

Silverware Games is a social network where people can play games online. Users can attach URLs to YouTube videos, the site will generate related `<iframe>` when the post will be published. The handler has some sort of protection so non-YouTube links can't be posted, as well as HTML tags are being stripped. However, it was still possible to add custom HTML attributes (e.g. `onclick=alert("xss")`) to the `<iframe>'. This issue was fixed in the version `1.1.34` and does not require any extra actions from our members. There has been no evidence that this vulnerability was used by anyone at this time.