message/index.php in Moodle through 2.5.9, 2.6.x before 2.6.9, 2.7.x before 2.7.6, and 2.8.x before 2.8.4 does not consider the moodle/site:readallmessages capability before accessing arbitrary conversations, which allows remote authenticated users to obtain sensitive personal-contact and unread-message-count information via a modified URL.
https://moodle.org/mod/forum/discuss.php?d=307380
http://openwall.com/lists/oss-security/2015/03/16/1
http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-49204