Form validation can be skipped

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

https://github.com/neos/form/commit/69de4219b1f58157e2be6b05811463875d75c246

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 https://github.com/neos/form/commit/049d415295be8d4a0478ccba97dba1bb81649567
Original report: https://tickets.neos.io/#ticket/zoom/411 (internal)