In Moodle 3.x, students can find out email addresses of other students in the same course. Using search on the Participants page, students could search email addresses of all participants regardless of email visibility. This allows enumerating and guessing emails of other students.
In Moodle 2.x and 3.x, a CSRF attack is possible that allows attackers to change the "number of courses displayed in the course overview block" configuration setting.
Cross-site scripting (XSS) vulnerabilities in Moodle CMS on or before 3.1.2 allow remote attackers to inject arbitrary web script or HTML via the s_additionalhtmlhead, s_additionalhtmltopofbody, and s_additionalhtmlfooter parameters.
Unrestricted file upload vulnerability in the double extension support in the "image" module in Moodle 3.1.2 allows remote authenticated users to execute arbitrary code by uploading a file with an executable extension, and then accessing it via unspecified vectors.