Comment 4 for bug 1908204

ufw by design is opinionated on traffic that is deemed essential and does not block outgoing ping6 even with the outgoing policy as deny. However, this opinion is expressed in /etc/ufw/before6.rules so that the admin may adjust according to site policies. I think you'll achieve your goals by commenting out '-A ufw6-before-input -p icmpv6 --icmpv6-type echo-request -j ACCEPT' from /etc/ufw/before6.rules and then reloading the firewall. Good luck!