Decidim is a participatory democracy framework, written in Ruby on Rails, originally developed for the Barcelona City government online and offline participation website. The external link feature is susceptible to cross-site scripting. This allows a remote attacker to execute JavaScript code in the context of a currently logged-in user. An attacker could use this vulnerability to make other users endorse or support proposals they have no intention of supporting or endorsing. The problem was patched in versions 0.27.3 and 0.26.7.

Decidim Cross-site Scripting vulnerability in the external link redirections