/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/ is in ruby-activesupport 2:4.2.10-0ubuntu4.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/access.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/behavior.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/conversions.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/exclude.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/filters.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/indent.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/inflections.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/inquiry.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/multibyte.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/output_safety.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/starts_ends_with.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/strip.rb
/usr/lib/ruby/vendor_ruby/active_support/core_ext/string/zones.rb