login/confirm.php in Moodle through 2.5.9, 2.6.x before 2.6.11, 2.7.x before 2.7.8, and 2.8.x before 2.8.6 allows remote authenticated users to bypass intended login restrictions by leveraging access to an unconfirmed suspended account.
https://github.com/advisories/GHSA-4ppg-2mx6-fqx9
https://moodle.org/mod/forum/discuss.php?d=313686
http://www.securitytracker.com/id/1032358
http://www.securityfocus.com/bid/74725
http://openwall.com/lists/oss-security/2015/05/18/1
http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-50090