diff -up doxygen-1.8.5/src/search_opensearch.php.than doxygen-1.8.5/src/search_opensearch.php
--- doxygen-1.8.5/src/search_opensearch.php.than	2019-07-25 13:23:49.988957523 +0200
+++ doxygen-1.8.5/src/search_opensearch.php	2019-07-25 13:24:16.842105308 +0200
@@ -3,6 +3,7 @@ require "search-functions.php";
 
 $mode = array_key_exists('v', $_GET)?$_GET['v']:"";
 $query = array_key_exists('query', $_GET)?$_GET['query']:"";
+$query = preg_replace("/[^a-zA-Z0-9\-\_\.\x80-\xFF]/i", " ", $query );
 
 $query_results = run_query($query);