Index: wp-includes/class-simplepie-kses.php
new file mode 100644
===================================================================
---wp-includes/class-simplepie-kses.php	(revision 0)n+++wp-includes/class-simplepie-kses.php	(revision 0)
@@ -0,0 +1,27 @@
+<?php
+/**
+ * WordPress extension of SimplePie sanitization
+ *
+ * Contains the WP_SimplePie_Sanitize_KSES class
+ *
+ * @package WordPress
+ */
+
+/**
+ * WordPress SimplePie Sanitization Class
+ *
+ * Extension of the SimplePie_Sanitize class to use KSES, because
+ * we cannot universally count on DOMDocument being available
+ *
+ * @package WordPress
+ * @since 3.5.0
+ */
+class WP_SimplePie_Sanitize_KSES extends SimplePie_Sanitize {
+	public function sanitize( $data, $type, $base = '' ) {
+		if ( $type & ( SIMPLEPIE_CONSTRUCT_HTML | SIMPLEPIE_CONSTRUCT_XHTML ) ) {
+			return wp_kses_post( $data );
+		} else {
+			return parent::sanitize( $data, $type, $base );
+		}
+	}
+}
Index: wp-includes/feed.php
===================================================================
--- wp-includes/feed.php	(revision 22804)
+++ wp-includes/feed.php	(working copy)
@@ -525,9 +525,15 @@ function feed_content_type( $type = '' ) {
  */
 function fetch_feed($url) {
 	require_once (ABSPATH . WPINC . '/class-feed.php');
+	require_once (ABSPATH . WPINC . '/class-simplepie-kses.php');
 
 	$feed = new SimplePie();
 
+	$feed->set_sanitize_class( 'WP_SimplePie_Sanitize_KSES' );
+	// We must manually overwrite $feed->sanitize because SimplePie's
+	// constructor sets it before we have a chance to set the sanitization class
+	$feed->sanitize = new WP_SimplePie_Sanitize_KSES();
+	
 	$feed->set_cache_class( 'WP_Feed_Cache' );
 	$feed->set_file_class( 'WP_SimplePie_File' );