A XSS risk exists in the returnURL parameter passed to dev/build. An unvalidated url could cause the user to redirect to an unverified third party url outside of the site.
This issue is resolved in framework 3.1.14 stable release.
github.com/FriendsOfPHP/security-advisories/blob/master/silverstripe/framework/SS-2015-015-1.yaml
github.com/silverstripe/silverstripe-framework
github.com/silverstripe/silverstripe-framework/commit/751d77386c3c6e354b521fa61ff142f95895cca8
www.silverstripe.org/software/download/security-releases/ss-2015-015