The LTI module in Moodle through 2.4.11, 2.5.x before 2.5.9, 2.6.x before 2.6.6, and 2.7.x before 2.7.3 does not properly restrict the parameters used in a return URL, which allows remote attackers to trigger the generation of arbitrary messages via a modified URL, related to mod/lti/locallib.php and mod/lti/return.php.