#!/usr/bin/nft -f flush ruleset table inet filter { define ip-allowlist-ssh = { 127.0.0.1, } define ip6-allowlist-ssh = { ::1, } set ip-connlimit-ssh { type ipv4_addr flags dynamic } set ip6-connlimit-ssh { type ipv6_addr flags dynamic } set ip-connlimit-main { type ipv4_addr flags dynamic } set ip6-connlimit-main { type ipv6_addr flags dynamic } chain prerouting-raw { type filter hook prerouting priority raw # drop packets without a reverse path (strict reverse path filtering) fib saddr . iif oif missing counter drop iif lo notrack accept # drop packets to address not configured on incoming interface (strong host model) # # ordered after accepting loopback to permit using external IPs via loopback fib daddr . iif type != { local, broadcast, multicast } counter drop # handle new TCP connections beyond rate limit via synproxy to avoid conntrack table exhaustion tcp dport { 22, 80, 443 } tcp flags syn limit rate 1024/second burst 128 packets accept tcp dport { 22, 80, 443 } tcp flags syn counter notrack accept meta l4proto { icmp, ipv6-icmp } notrack accept } chain input { type filter hook input priority filter policy drop tcp dport { 22, 80, 443 } goto input-tcp-service iif lo accept meta l4proto { icmp, ipv6-icmp } accept ct state vmap { new : goto graceful-reject, established : accept, related : accept } } chain input-tcp-service { iif lo goto input-tcp-service-loopback # for synproxy, SYN is untracked and first ACK is invalid which are handled via fallthrough ct state vmap { new : goto input-tcp-service-new, established : goto input-tcp-service-established, related : accept } tcp dport 22 ip saddr @ip-connlimit-ssh counter reject with tcp reset tcp dport 22 ip6 saddr and ffff:ffff:ffff:ffff:ffff:: @ip6-connlimit-ssh counter reject with tcp reset tcp dport { 80, 443 } ip saddr @ip-connlimit-main counter reject with tcp reset tcp dport { 80, 443 } ip6 saddr and ffff:ffff:ffff:ffff:: @ip6-connlimit-main counter reject with tcp reset synproxy mss 1460 wscale 7 timestamp sack-perm } chain input-tcp-service-new { tcp dport 22 ip saddr @ip-connlimit-ssh counter reject with tcp reset tcp dport 22 ip6 saddr and ffff:ffff:ffff:ffff:ffff:: @ip6-connlimit-ssh counter reject with tcp reset tcp dport { 80, 443 } ip saddr @ip-connlimit-main counter reject with tcp reset tcp dport { 80, 443 } ip6 saddr and ffff:ffff:ffff:ffff:: @ip6-connlimit-main counter reject with tcp reset accept } # add connections established without synproxy to connection limit sets with limits enforced chain input-tcp-service-established { ct mark 0x1 accept tcp dport 22 ip saddr != $ip-allowlist-ssh add @ip-connlimit-ssh { ip saddr ct count over 1 } counter reject with tcp reset tcp dport 22 ip6 saddr != $ip6-allowlist-ssh add @ip6-connlimit-ssh { ip6 saddr and ffff:ffff:ffff:ffff:ffff:: ct count over 1 } counter reject with tcp reset tcp dport { 80, 443 } add @ip-connlimit-main { ip saddr ct count over 32 } counter reject with tcp reset tcp dport { 80, 443 } add @ip6-connlimit-main { ip6 saddr and ffff:ffff:ffff:ffff:: ct count over 32 } counter reject with tcp reset ct mark set 0x1 accept } # add connections established with synproxy to connection limit sets with limits enforced chain input-tcp-service-loopback { tcp flags != syn accept tcp dport 22 ip saddr != $ip-allowlist-ssh add @ip-connlimit-ssh { ip saddr ct count over 1 } counter reject with tcp reset tcp dport 22 ip6 saddr != $ip6-allowlist-ssh add @ip6-connlimit-ssh { ip6 saddr and ffff:ffff:ffff:ffff:ffff:: ct count over 1 } counter reject with tcp reset tcp dport { 80, 443 } add @ip-connlimit-main { ip saddr ct count over 32 } counter reject with tcp reset tcp dport { 80, 443 } add @ip6-connlimit-main { ip6 saddr and ffff:ffff:ffff:ffff:: ct count over 32 } counter reject with tcp reset ct mark set 0x1 accept } chain forward { type filter hook forward priority filter policy drop } chain output-raw { type filter hook output priority raw oif lo notrack accept meta l4proto { icmp, ipv6-icmp } notrack accept } chain output { type filter hook output priority filter oif lo goto output-loopback skuid != { root, systemd-network, unbound, chrony, http, attestation } counter goto graceful-reject } chain output-loopback { skuid unbound meta l4proto { tcp, udp } th sport 53 th dport >= 1024 th dport != 8080 accept skuid { chrony, attestation } meta l4proto { tcp, udp } th sport >= 1024 th sport != 8080 th dport 53 accept skuid attestation tcp sport 8080 tcp dport >= 1024 tcp dport != 8080 accept skuid http tcp sport >= 1024 tcp sport != 8080 tcp dport 8080 accept skuid != root counter goto graceful-reject accept } chain graceful-reject { meta l4proto udp reject meta l4proto tcp reject with tcp reset reject } }