If you set "editor.contentFilter.allowIFrame" value to false, insertion of <iframe> tag by the user is restricted and the tag is automatically removed.

{
	'editor.contentFilter.allowIFrame': false
}

If you set "editor.contentFilter.allowIScript" value to false, insertion of <script> tag by the user is restricted and the tag is automatically removed.

{
	'editor.contentFilter.allowScript': false
}