The core_enrol_get_enrolled_users web service in enrol/externallib.php in Moodle through 2.6.11, 2.7.x before 2.7.11, 2.8.x before 2.8.9, and 2.9.x before 2.9.3 does not properly implement group-based access restrictions, which allows remote authenticated users to obtain sensitive course-participant information via a web-service request.
git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-51861
github.com/moodle/moodle
github.com/moodle/moodle/commit/12bc713081dc24b6eedea54281876e7c3f5579a6
github.com/moodle/moodle/commit/512633461ae239677342b40d318803e15e1fd1aa
github.com/moodle/moodle/commit/b26b2407908abb1a8a4d37aebc18e03139c9776f
moodle.org/mod/forum/discuss.php?d=323234
nvd.nist.gov/vuln/detail/CVE-2015-5339