CVE 2013-2080
The core_grade component in Moodle through 2.2.10, 2.3.x before 2.3.7, and 2.4.x before 2.4.4 does not properly consider the existence of hidden grades, which allows remote authenticated users to obtain sensitive information by leveraging the student role and reading the Gradebook Overview report.
See the 
CVE page on Mitre.org
for more details.
