--- a/Classes/Utility/GeneralUtility.php
+++ b/Classes/Utility/GeneralUtility.php	(date 1676644649547)
@@ -2076,8 +2076,9 @@
             }

             foreach ($allowedFileExtensionArray as $allowedFileExtension) {
+                $allowedFileExtension = '.'.$allowedFileExtension;
                 if (
-                    ($extensionList === ',,' || stripos($extensionList, ',' . substr($entry, strlen($allowedFileExtension) * -1, strlen($allowedFileExtension)) . ',') !== false)
+                    ($extensionList === ',,' ||  strtolower(substr($entry, strlen($allowedFileExtension) * -1)) === $allowedFileExtension)
                     && ($excludePattern === '' || !preg_match('/^' . $excludePattern . '$/', $entry))
                 ) {
                     if ($order !== 'mtime') {