Contao is an Open Source CMS. In versions starting from 5.0.0 and prior to 5.3.38 and 5.6.1, if a news feed contains protected news archives, their news items are not filtered and become publicly available in the RSS feed. This issue has been patched in versions 5.3.38 and 5.6.1. A workaround involves not adding protected news archives to the news feed page.
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.