I know CU support has been a source of much interest over the recent months and last week Microsoft released CU8 which further complicated things.
However, we had been anticipating the release of CU8 and our QA guys have worked hard over the last week to certify it. So we're pleased to say that it is now supported and the certification guide will be updated shortly, but hope this news will make all your lives a lot easier and allow you to upgrade to the latest version of Exchange 2013.
This news is also referenced on the Engineering blog - http://www.symantec.com/connect/blogs/exchange-2013-cu8-certification
For full details on what EV versions support CU8 - please refer to this technote.
http://www.symantec.com/business/support/index?page=content&id=TECH225267