calendar/managesubscriptions.php in the Manage Subscriptions implementation in Moodle 2.4.x before 2.4.1 omits a capability check, which allows remote authenticated users to remove course-level calendar subscriptions by leveraging the student role and sending an iCalendar object.
Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.