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.
https://moodle.org/mod/forum/discuss.php?d=220163
http://openwall.com/lists/oss-security/2013/01/21/1
http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-37244