Last September 1st, the latest version of Ruby on Rails 4.2.4 and 4.1.13 has finally been released.
This release includes quite a few bug fixes across multiple gems. Notable fixes such as in 4.1.13 ActiveRecord to not define autosave association callbacks twice from accept_nested_attributes_for. Rails 4.2.4 has more fixes included, one also in ActiveRecord that if the through class has default scopes, it should skip the statement cache for the model. There is also a fix in ActiveSupport that causes a SystemStackError when encoding an Enumerable with json gem while having the ActiveSupport JSON encoder loaded at the same time. Visit the change log for each gem to view the fixes applied to this release.
Do note that there are no changes regarding any security fixes which means upgrading to these versions are optimal but not critical. These are solid updates on the code before Rails 5 is released this year in which I am really excited to finally get my hands on.
Bit Clarity 