Contao 4.0 through 4.8.5 allows PHP local file inclusion. A back end user with access to the form generator can upload arbitrary files and execute them on the server.
https://github.com/advisories/GHSA-wjx8-cgrm-hh8p
https://euvd.enisa.europa.eu/vulnerability/EUVD-2019-0804
https://contao.org/en/security-advisories/unrestricted-file-uploads.html