AFter adding an RSS Viewer web part onto your desired page, if you may notice the headlines& content only being visible when the page is checked out, add a script editor web part to the same page that you have the RSS Viewer. In it, add the following code:
<Script Type="text/javascript">
function CustomUpdateFormDigest()
{
if(window._spPageContextInfo != null)
{
var $v_2 = window._spPageContextInfo;
var $v_3 = $v_2.webServerRelativeUrl;
var $v_4 = window._spFormDigestRefreshInterval;
UpdateFormDigest($v_3, $v_4);
}
}
CustomUpdateFormDigest();
</Script>
I found this solution here: http://social.technet.microsoft.com/Forums/sharepoint/en-US/98a4e93e-5073-4b39-b379-6cc3eed2d984/rss-viewer-web-part-not-working-after-installing-kb2767793?forum=sharepointgeneralprevious
They also recommended adding it to the Master Page, or turning off security validation for the pages containing the RSS Viewer web part via Central Admin->Web Application->General Settings.