The enrol_meta_sync function in enrol/meta/locallib.php in Moodle through 2.6.11, 2.7.x before 2.7.10, 2.8.x before 2.8.8, and 2.9.x before 2.9.2 allows remote authenticated users to obtain manager privileges in opportunistic circumstances by leveraging incorrect role processing during a long-running sync script.
https://moodle.org/mod/forum/discuss.php?d=320290
http://www.securitytracker.com/id/1033619
http://www.openwall.com/lists/oss-security/2015/09/21/1
http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-50744