/usr/lib/ruby/vendor_ruby/ is in ruby-mustache 0.99.6-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/rack/bug/
/usr/lib/ruby/vendor_ruby/rack/
/usr/lib/ruby/vendor_ruby/rack/bug/panels/
/usr/lib/ruby/vendor_ruby/rack/bug/panels/mustache_panel.rb
/usr/lib/ruby/vendor_ruby/rack/bug/panels/mustache_panel/
/usr/lib/ruby/vendor_ruby/rack/bug/panels/mustache_panel/mustache_extension.rb
/usr/lib/ruby/vendor_ruby/rack/bug/panels/mustache_panel/view.mustache
/usr/lib/ruby/vendor_ruby/mustache.rb
/usr/lib/ruby/vendor_ruby/mustache/
/usr/lib/ruby/vendor_ruby/mustache/enumerable.rb
/usr/lib/ruby/vendor_ruby/mustache/parser.rb
/usr/lib/ruby/vendor_ruby/mustache/generator.rb
/usr/lib/ruby/vendor_ruby/mustache/context.rb
/usr/lib/ruby/vendor_ruby/mustache/version.rb
/usr/lib/ruby/vendor_ruby/mustache/sinatra.rb
/usr/lib/ruby/vendor_ruby/mustache/blah.rb
/usr/lib/ruby/vendor_ruby/mustache/template.rb
/usr/lib/ruby/vendor_ruby/mustache/settings.rb