GridField does not have sufficient CSRF protection, meaning that in some cases users with CMS access can be tricked into posting unspecified data into the CMS from external websites. Amongst other default CMS interfaces, GridField is used for management of groups, users and permissions in the CMS.
The resolution for this issue is to ensure that all gridFieldAlterAction submissions are checked for the SecurityID token during submission.
github.com/FriendsOfPHP/security-advisories/blob/master/silverstripe/framework/SS-2016-002-1.yaml
github.com/silverstripe/silverstripe-framework
github.com/silverstripe/silverstripe-framework/commit/013524af5069bb0cf909853f04418d9bef56d18c
github.com/silverstripe/silverstripe-framework/commit/56e92f5a32e45849cc9361c8603c31d7010c9d36
github.com/silverstripe/silverstripe-framework/commit/e2c77c5a8f13e901c51a3684210811559b592f0c
www.silverstripe.org/download/security-releases/ss-2016-002