A vulnerability was found in moodle before versions 3.4.8, 3.5.x before 3.5.5 and 3.6.x before 3.6.3. Permissions were not correctly checked before loading event information into the calendar's edit event modal popup, so logged in non-guest users could view unauthorised calendar events. (Note: It was read-only access, users could not edit the events.)
CWE-863 - Incorrect Authorization
Authorization is a security mechanism performed by an application to grant or deny access to the requested resources by verifying the privileges of the user. When an application lacks effective authorization mechanisms, it enables unauthorized users to gain unintended privileges and illegitimate access to resources. Such a vulnerability may result in exposure of sensitive information, denial of service, arbitrary code execution, and complete system takeover.