Atto in Moodle 2.8.x before 2.8.9 and 2.9.x before 2.9.3 allows remote attackers to cause a denial of service (disk consumption) by leveraging the guest role and entering drafts with the editor-autosave feature.
https://moodle.org/mod/forum/discuss.php?d=323229
http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-51000