Teaser needs filtering before display

The default output for premium content to non subscribers doesn't filter the nodes teaser text before display. THis means undesirable content may appear.

The $node->teaser should be passed through the check_markup() function to make sure it's safe.

A better theme function would be:

function theme_premium_body($node) {
  return check_markup($node->teaser, $node->format, FALSE) . '<br />'.variable_get('premium_message','');
}