nftables/nat.nft
Phil Sutter 8d211afc1d nftables-1.0.4-3.el9
* Fri Nov 25 2022 Phil Sutter <psutter@redhat.com> [1.0.4-3.el9]
- Prevent port-shadow attacks in sample nat config (Phil Sutter) [2061940]
Resolves: rhbz#2061940
2022-11-25 16:48:10 +01:00

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# Sample configuration snippet for nftables service.
# Meant to be included by main.nft, not for direct use.
# dedicated table for IPv4
table ip nftables_svc {
# interfaces to masquerade traffic from
set masq_interfaces {
type ifname
elements = { "virbr0" }
}
# networks to masquerade traffic from
# 'interval' flag is required to support subnets
set masq_ips {
type ipv4_addr
flags interval
elements = { 192.168.122.0/24 }
}
# force port randomization for non-locally originated connections using
# suspicious port values to prevent port-shadow attacks, i.e.
# accidental matching of new inbound connections vs. existing ones
chain do_masquerade {
meta iif > 0 th sport < 16384 th dport >= 32768 masquerade random
masquerade
}
# base-chain to manipulate conntrack in postrouting,
# will see packets for new or related traffic only
chain POSTROUTING {
type nat hook postrouting priority srcnat + 20
policy accept
iifname @masq_interfaces oifname != @masq_interfaces jump do_masquerade
ip saddr @masq_ips jump do_masquerade
}
}