A flaw was found in moodle before versions 3.5.1, 3.4.4, 3.3.7, 3.1.13. It was possible for the corecourseget_categories web service to return hidden categories, which should be omitted when fetching course categories.
{ "binaries": [ { "binary_name": "moodle", "binary_version": "3.0.3+dfsg-0ubuntu1" } ] }