Index: wp-includes/comment.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- wp-includes/comment.php	(revision d229e92d1407afe192b704cefc7fb387e9105966)
+++ wp-includes/comment.php	(revision )
@@ -1976,29 +1976,21 @@
 
 	$parsed_home = @parse_url( get_option( 'home' ) );
 
-	$same_host = strtolower( $parsed_home['host'] ) === strtolower( $parsed_url['host'] );
+	$same_host = strcasecmp( $parsed_home['host'], $parsed_url['host'] ) === 0;
 
 	if ( ! $same_host ) {
 		$host = trim( $parsed_url['host'], '.' );
-		if ( preg_match( '#^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$#', $host ) ) {
-			$ip = $host;
-		} else {
+		$ip = filter_var( $host, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4 );
+		if ( ! $ip ) {
 			$ip = gethostbyname( $host );
 			if ( $ip === $host ) // Error condition for gethostbyname()
 				$ip = false;
 		}
 		if ( $ip ) {
-			if ( '127.0.0.1' === $ip )
+			if ( ! filter_var( $ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4 | FILTER_FLAG_NO_RES_RANGE | FILTER_FLAG_NO_PRIV_RANGE ) ) {
 				return '';
-			$parts = array_map( 'intval', explode( '.', $ip ) );
-			if ( 10 === $parts[0] )
-				return '';
-			if ( 172 === $parts[0] && 16 <= $parts[1] && 31 >= $parts[1] )
-				return '';
-			if ( 192 === $parts[0] && 168 === $parts[1] )
-				return '';
-		}
-	}
+			}
+		}
 
 	if ( empty( $parsed_url['port'] ) )
 		return $uri;
@@ -2007,7 +1999,7 @@
 	if ( 80 === $port || 443 === $port || 8080 === $port )
 		return $uri;
 
-	if ( $parsed_home && $same_host && $parsed_home['port'] === $port )
+	if ( $same_host && isset( $parsed_home['port'] ) && $parsed_home['port'] === $port )
 		return $uri;
 
 	return '';