admin/uploaduser_form.php in Moodle 2.0.x before 2.0.3 does not force password changes for autosubscribed users, which makes it easier for remote attackers to obtain access by leveraging knowledge of the initial password of a new user.
http://openwall.com/lists/oss-security/2011/11/14/1
http://moodle.org/mod/forum/discuss.php?d=175588
http://git.moodle.org/gw?p=moodle.git%3Ba=commit%3Bh=22a77963439e00441949440f0517135b3a5418da