Validate target domain for CNAME records

Signed-off-by: yubiuser <ckoenig@posteo.de>

scripts/pi-hole/php/func.php

@@ -302,6 +302,9 @@ function addCustomCNAMEEntry($domain="", $target="", $json=true)
         if (empty($target))
             return returnError("Target must be set", $json);
 
+        if (!is_valid_domain_name($target))
+            return returnError("Trget must be valid", $json);
+
         // Check if each submitted domain is valid
         $domains = array_map('trim', explode(",", $domain));
         foreach ($domains as $d) {