The Contact Form by Supsystic WordPress plugin before 1.11.1 does not sandbox the template...

The Contact Form by Supsystic WordPress plugin before 1.11.1 does not sandbox the template engine used to render its forms and allows stored form-editor content to reach that engine as executable template code, enabling an administrator to perform server-side template injection and execute arbitrary code on the server. The injected template is compiled and executed whenever any visitor loads a page containing the form, so the stored payload also lets an unauthenticated visitor read server-side secrets such as authentication salts and database credentials.