Source of inspiration:
[Tails-dev] Reducing attack surface of kernel and tightening firewall/sysctls
https://www.mail-archive.com/tails-dev@boum.org/msg07483.html
In https://github.com/Whonix/whonix-gw-firewall/blob/master/usr/bin/whonix_firewall#L249
changing
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
to
iptables -A INPUT -m state --state ESTABLISHED -j ACCEPT
Currently testing on my local machine.
Other testers welcome.