LORIS (Longitudinal Online Research and Imaging System) is a self-hosted web application that provides data- and project-management for neuroimaging research. From to before 27.0.3 and 28.0.1, the help_editor module of LORIS did not properly sanitize some user supplied variables which could result in a reflected cross-site scripting attack if a user is tricked into following an invalid link. The same input vector could also allow an attacker to download arbitrary markdown files on an unpatched server. This vulnerability is fixed in 27.0.3 and 28.0.1.