The lesson module 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 bypass intended access restrictions and enter additional answer attempts by leveraging the student role.
https://moodle.org/mod/forum/discuss.php?d=320287
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-50516