JCE is a very popular content editor for Joomla! sites. A vulnerability has been reported in JCE 2.0 and JCE 1.5 that allows a logged in user - who has access to JCE (ie: they can created or edit articles) and any of the Image Manager, Image Manager Extended, File Manager, Media Manager or Template Manager plugins - to view and manipulate files and folders outside of the folder assigned to these plugins.
JCE 2.0.11 and JCE 126.96.36.199 add additional security checks to fix the vulnerability. Additional checks have also been added to some functions in the Image Manager Extended and Template Manager plugins.
Upgrade JCE to the latest version.