A high level XSS risk has been identified in the encoding of validation messages in certain FormField classes.
Certain fields such as the NumericField and DropdownField have been identified, but any form field which presents any invalid content as a part of its validation response will be at risk.
github.com/FriendsOfPHP/security-advisories/blob/master/silverstripe/framework/SS-2015-026-1.yaml
github.com/silverstripe/silverstripe-framework
github.com/silverstripe/silverstripe-framework/commit/245e0aae2f5f3eb0acba1d198ad8e196bb224462
github.com/silverstripe/silverstripe-framework/commit/bc1b2893accba6401c03f9ea3b0cbc4621c7a02c
www.silverstripe.org/download/security-releases/ss-2015-026