/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/ is in ruby-merb-core 1.1.3+dfsg-2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/abstract.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/ebb.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/evented_mongrel.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/fcgi.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/irb.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/mongrel.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/runner.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/swiftiplied_mongrel.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/thin.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/thin_turbo.rb
/usr/lib/ruby/vendor_ruby/merb-core/rack/adapter/webrick.rb