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.