comment/lib.php in Moodle 2.0.x before 2.0.4 and 2.1.x before 2.1.1 does not properly restrict comment capabilities, which allows remote attackers to post a comment by leveraging the guest role and operating on a front-page activity.
Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.