Directory traversal vulnerability in wp-admin/admin.php in the DMSGuestbook 1.8.0 and 1.7.0 plugin for WordPress allows remote authenticated users to read arbitrary files via a .. (dot dot) in the (1) folder and (2) file parameters.
https://www.exploit-db.com/exploits/5035
http://www.securityfocus.com/archive/1/487437/100/0/threaded