The generate_password function in Moodle through 2.4.11, 2.5.x before 2.5.9, 2.6.x before 2.6.6, and 2.7.x before 2.7.3 does not provide a sufficient number of possible temporary passwords, which allows remote attackers to obtain access via a brute-force attack.
https://moodle.org/mod/forum/discuss.php?d=275152
http://www.securitytracker.com/id/1031215
http://openwall.com/lists/oss-security/2014/11/17/11
http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-47050