Index: wp-includes/class-http.php
===================================================================
--- wp-includes/class-http.php	(revision 25952)
+++ wp-includes/class-http.php	(working copy)
@@ -525,9 +525,17 @@
 		static $accessible_hosts;
 		static $wildcard_regex = false;
 		if ( null == $accessible_hosts ) {
-			$accessible_hosts = preg_split('|,\s*|', WP_ACCESSIBLE_HOSTS);

-			if ( false !== strpos(WP_ACCESSIBLE_HOSTS, '*') ) {
+			/**
+			 * Filter the list of accessible hosts.
+			 *
+			 * @since 3.8
+			 *
+			 * @param array List of accessible hosts
+			 */
+			$accessible_hosts = apply_filters( 'wp_http_accessible_hosts', preg_split( '|,\s*|', WP_ACCESSIBLE_HOSTS ) );
+
+			if ( false !== strpos( WP_ACCESSIBLE_HOSTS, '*' ) ) {
 				$wildcard_regex = array();
 				foreach ( $accessible_hosts as $host )
 					$wildcard_regex[] = str_replace( '\*', '.+', preg_quote( $host, '/' ) );