add_action('generate_rewrite_rules', 'attachment_rewrite_rule_14924');

function attachment_rewrite_rule_14924($wp_rewrite){
  $newrules = array();
  $new_rules['?media=(\d*)$'] = 'index.php?attachment_id=$matches[1]';
  $wp_rewrite->rules = $new_rules + $wp_rewrite->rules;
}