Contao before 4.4.52, 4.9.x before 4.9.6, and 4.10.x before 4.10.1 have Improper Input Validation. It is possible to inject insert tags in front end forms which will be replaced when the page is rendered.
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.
Contao 4.0 through 4.8.5 has Insecure Permissions. Back end users can manipulate the details view URL to show pages and articles that have not been enabled for them.