Decidim vulnerable to data disclosure through the embed feature

Decidim is a participatory democracy framework, written in Ruby on Rails, originally developed for the Barcelona City government online and offline participation website. If an attacker can infer the slug or URL of an unpublished or private resource, and this resource can be embbeded (such as a Participatory Process, an Assembly, a Proposal, a Result, etc), then some data of this resource could be accessed. This vulnerability is fixed in 0.27.6.