It's almost certainly a network-based firewall, not a host-based one. And if you use multiple firewalls from multiple vendors with different OSes running on the

It's almost certainly a network-based firewall, not a host-based one. And if you use multiple firewalls from multiple vendors with different OSes running on the firewalls, theoretically, an attacker could have zero days on all of them, but it's statistically much less likely than an attacker having a zero day on only one popular consumer/server OS.