Form validation can be skipped in neos/form

Description Impact By crafting a special GET request containing a valid form state, a form can be submitted without invoking any validators. We consider the severity low because it is not possible to change any form values since the form state is secured with an HMAC that is still verified. That means that this issue can only be exploited if Form Finishers cause side effects even if no form values have been sent. Patches 69de421 Workarounds Form Finishers can be adjusted in a way that they only execute an action if the submitted form contains some expected data. Alternatively a custom Finisher can be added as first finisher. References This regression was introduced with 049d415 Original report: https://tickets.neos.io/#ticket/zoom/411 (internal)