Serendipity before 2.1.5 has XSS via EXIF data that is mishandled in the templates/2k11/admin/media_choose.tpl Editor Preview feature or the templates/2k11/admin/media_items.tpl Media Library feature.
https://www.openwall.com/lists/oss-security/2019/05/03/3
https://github.com/s9y/Serendipity/issues/598
https://blog.s9y.org/archives/282-Serendipity-2.1.5-released.html