Strip port numbers from root page domains

core-bundle/src/Resources/contao/dca/tl_page.php

@@ -1282,7 +1282,16 @@ public function loadDns($varValue)
 	 */
 	public function checkDns($varValue)
 	{
-		return Idna::encode(preg_replace('#^(?:[a-z]+://)?([\pN\pL[\].:_-]+).*$#iu', '$1', $varValue));
+		if (!$varValue)
+		{
+			return '';
+		}
+
+		// The first part will match IPv6 addresses in square brackets. The
+		// second part will match domain names and IPv4 addresses.
+		preg_match('#(?:^(?:[a-z]+]://)?(\[[0-9a-f:]+]))|(?:^(?:[a-z]+://)?([\pN\pL._-]*))#ui', $varValue, $matches);
+
+		return Idna::encode($matches[2] ?? $matches[1]);
 	}
 
 	/**