WHAT'S HAPPENING?
Apple has released a security update which patches a critical vulnerability that allows local accounts to gain escalated privileges.  The fix is found in update 10.10.3 and Security Update 2015-004 (for machines below OS X 10.10).  Unfortunately, the vulnerability is present in OS X 10.7 (Lion), but Apple has not yet released a patch for Lion (nor have they stated whether a patch is forthcoming).
 
 
WHO IS AFFECTED?
Users of Mac OS X 10.7 and above.
 
 
WHAT DO YOU NEED TO DO?