typically issues are fixed in master. So you can inspect the current master branch on https://github.com/liferay/liferay-portal. The commits have a reference to the Jira ticket number. Identify what has been done, backport that patch to your version (as plugin or as change to source)
Upgrading to EE is another way: Liferay support will do these steps for you and provide a fixpack or hotfix.
