graphene-os-server-infrastr.../nftables-ns2.conf
Daniel Micay 8c929f02ac enforce IPv6 SSH connection limit for /48 blocks
Since our primary servers using SSH to mirror their TLS certificates to
replicas are now allowlisted, we can use a stricter block size than we
could with the PerSourceMaxStartups approach in sshd.
2024-03-28 11:38:06 -04:00

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#!/usr/bin/nft -f
flush ruleset
table inet filter {
define ip-allowlist-ssh = {
127.0.0.1,
198.98.53.141, # 0.ns2.grapheneos.org
}
define ip6-allowlist-ssh = {
::1,
2605:6400:10:102e:95bc:89ef:2e7f:49bb, # 0.ns2.grapheneos.org
}
set ip-connlimit-ssh {
type ipv4_addr
flags dynamic
}
set ip6-connlimit-ssh {
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)
fib daddr . iif type != { local, broadcast, multicast } counter drop
# reject SSH packets via anycast IP
tcp dport 22 ip daddr 198.251.90.93 reject with tcp reset
udp dport 53 notrack accept
tcp dport { 53, 80, 443, 853 } notrack accept
tcp dport 22 tcp flags syn notrack accept
meta l4proto { icmp, ipv6-icmp } notrack accept
}
chain output-raw {
type filter hook output priority raw
oif lo notrack accept
udp sport 53 notrack accept
tcp sport { 53, 80, 443, 853 } notrack accept
meta l4proto { icmp, ipv6-icmp } notrack accept
}
chain input {
type filter hook input priority filter
policy drop
iif lo tcp dport 22 tcp flags syn ip saddr != $ip-allowlist-ssh add @ip-connlimit-ssh { ip saddr ct count over 1 } reject with tcp reset
iif lo tcp dport 22 tcp flags syn ip6 saddr != $ip6-allowlist-ssh add @ip6-connlimit-ssh { ip6 saddr and ffff:ffff:ffff:ffff:ffff:: ct count over 1 } reject with tcp reset
iif lo accept
udp dport 53 accept
tcp dport { 53, 80, 443, 853 } accept
meta l4proto { icmp, ipv6-icmp } accept
ct state vmap { established : accept, related : accept, new : goto graceful-reject }
tcp dport 22 ip saddr @ip-connlimit-ssh reject with tcp reset
tcp dport 22 ip6 saddr and ffff:ffff:ffff:ffff:ffff:: @ip6-connlimit-ssh reject with tcp reset
tcp dport 22 synproxy mss 1460 wscale 7 timestamp sack-perm
}
chain forward {
type filter hook forward priority filter
policy drop
}
chain output {
type filter hook output priority filter
oif lo goto output-internal
skuid != { root, systemd-network, unbound, chrony, http, powerdns, geoipupdate } counter goto graceful-reject
}
chain output-internal {
skuid unbound meta l4proto { tcp, udp } th sport 53 th dport >= 1024 accept
skuid { chrony, geoipupdate } meta l4proto { tcp, udp } th sport >= 1024 th dport 53 accept
skuid powerdns meta l4proto tcp th sport 54 th dport >= 1024 accept
skuid http meta l4proto { tcp, udp } th sport >= 1024 th dport 54 accept
skuid powerdns meta l4proto tcp th sport 81 th dport >= 1024 accept
skuid != root counter goto graceful-reject
accept
}
chain graceful-reject {
meta l4proto udp reject
meta l4proto tcp reject with tcp reset
reject
}
}