notes/edit.php in Moodle 1.9.x through 1.9.19, 2.x through 2.1.10, 2.2.x before 2.2.8, 2.3.x before 2.3.5, and 2.4.x before 2.4.2 allows remote authenticated users to reassign notes via a modified (1) userid or (2) courseid field.