lib.php in the Submission comments plugin in the Assignment module in Moodle 2.3.x before 2.3.4 and 2.4.x before 2.4.1 allows remote attackers to read or modify the submission comments (aka feedback comments) of arbitrary users via a crafted URI.
Weaknesses in this category are related to the management of permissions, privileges, and other security features that are used to perform access control.