Contao is an open source content management system. Prior to versions 4.9.40, 4.13.21, and 5.1.4, logged in users can list arbitrary system files in the file manager by manipulating the Ajax request. However, it is not possible to read the contents of these files. Users should update to Contao 4.9.40, 4.13.21 or 5.1.4 to receive a patch. There are no known workarounds.