Cross-site scripting (XSS) vulnerability in the quiz_question_tostring function in mod/quiz/editlib.php in Moodle through 2.3.11, 2.4.x before 2.4.9, 2.5.x before 2.5.5, and 2.6.x before 2.6.2 allows remote authenticated users to inject arbitrary web script or HTML via a quiz question.