Craft CMS is a content management system (CMS). In versions 5.6.0 through 5.9.14, the actionSavePermissions() endpoint allows a user with only viewUsers permission to remove arbitrary users from all user groups. While _saveUserGroups() enforces per-group authorization for additions, it performs no equivalent authorization check for removals, so submitting an empty groups value removes all existing group memberships. Version 5.9.15 contains a patch.