geminabox (aka Gem in a Box) before 0.13.6 has XSS, as demonstrated by uploading a gem file that has a crafted gem.homepage value in its .gemspec file.
https://github.com/advisories/GHSA-98hq-3qvg-pg78
https://github.com/geminabox/geminabox/blob/master/CHANGELOG.md