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Firewall avansat

nftables

Tabele: ip (implicit), arp, ip6, bridge, inet, netdev.

Lanturi:

 filter: Supported by arp, bridge, ip, ip6 and inet table families.
 route: Mark packets (like mangle for the output hook, for other hooks use the type filter instead), supported by ip and ip6.
 nat: In order to perform Network Address Translation, supported by ip and ip6.

Hook: Se refera la stadiul acelui pachet in timp ce este procesat de kernel in Netfilter.

 The hooks for ip, ip6 and inet families are: prerouting, input, forward, output, postrouting.
 The hooks for arp family are: input, output.
 The bridge family handles ethernet packets traversing bridge devices.
 The hooks for netdev are: ingress, egress.

 % nft (add | create) chain [<family>] <table> <name> [ \{ type <type> hook <hook> [device <device>] priority <priority> \; [policy (accept | drop) \;] \} ]
 % nft (delete | list | flush) chain [<family>] <table> <name>
 % nft rename chain [<family>] <table> <name> <newname>

Reguli: nft (add | insert | replace | displace) rule

Exemplu 1, imitare iptables

Exemplu de reguli nftables, de importat cu comanda nft -f. O parte din chain-uri imita iptables. Nota: unele distributii acum implementeaza propriile reguli, de recomandat folosita comanda "flush ruleset" inainte.

table inet filter {
        chain input {
                type filter hook input priority filter;

                # Allow loopback (local connections)
                iifname lo accept

                # Allow established/related
                ct state established,related accept

                # Allow incoming pings
                ip protocol icmp limit rate 1/second accept

                # Allow SSH and HTTP
                tcp dport {ssh,http} accept

                # Drop everything else
                drop
        }
        chain forward {
                type filter hook forward priority filter;

                # Disallow forwarding
                drop
        }
        chain output {
                type filter hook output priority filter;

                # Allow all outgoing traffic
                accept
        }
}

Exemplu 2, prioritati

table ip filter {
        # This chain is evaluated first due to priority
        chain services {
                type filter hook input priority 0; policy accept;

                # If matched, this rule will prevent any further evaluation
                tcp dport http drop

                # If matched, and despite the accept verdict, the packet proceeds to enter the chain below
                tcp dport ssh accept

                # Likewise for any packets that get this far and hit the default policy
        }

        # This chain is evaluated last due to priority
        chain input {
                type filter hook input priority 1; policy drop;
                # All ingress packets end up being dropped here!
        }
}

Exemplu 3, log

table inet firewall {
    chain inbound {                                                              

        # By default, drop all traffic unless it meets a filter
        # criteria specified by the rules that follow below.
        type filter hook input priority 0; policy drop;

        # Allow traffic from established and related packets, drop invalid
        ct state vmap { established : accept, related : accept, invalid : drop } 

        # Allow loopback traffic.
        iifname lo accept

        tcp dport { 22, 80, 443, 55291, 5900 } accept
                                                                                                                                                                                                                                                                                          
        # Uncomment to enable logging of denied inbound traffic                                                                                                                                                                                                                           
        log prefix "[nftables] Inbound Denied: " counter drop                                                                                                                                                                                                                             
    }                                                                                                                                                                                                                                                                                     
}

Operatii la nivel de ruleset

listing

Listing the complete ruleset:

% nft list ruleset

Listing the ruleset per family:

% nft list ruleset arp
% nft list ruleset ip
% nft list ruleset ip6
% nft list ruleset bridge
% nft list ruleset inet

These commands will print all tables/chains/sets/rules of the given family.

flushing

In addition, you can also flush (erase, delete, wipe) the complete ruleset:

% nft flush ruleset

Also per family:

% nft flush ruleset arp
% nft flush ruleset ip
% nft flush ruleset ip6
% nft flush ruleset bridge
% nft flush ruleset inet

backup/restore

You can combine these two commands above to backup your ruleset:

% echo "flush ruleset" > backup.nft
% nft list ruleset >> backup.nft

And load it atomically:

% nft -f backup.nft

Listing in JSON format

You can also export your ruleset in JSON format, just pass the '--json' option:

% nft --json list ruleset > ruleset.json

Creare regula blocare ip-uri (nativa)

-functia ipv(4|6)_validate este un grep pe clase de ip-uri, nu este necesar pentru o lista simpla.

-Numarul de reguli verificabil cu " nft list table inet filter | grep -oc ',' "

echo '
add table inet filter
add chain inet filter INPUT { type filter hook input priority 1 ; }
add set inet filter ipmaster { flags interval; type ipv4_addr; auto-merge; }
add set inet filter ipmaster6 { flags interval; type ipv6_addr; auto-merge; }
insert rule inet filter INPUT ip saddr @ipmaster counter drop
insert rule inet filter INPUT ip6 saddr @ipmaster6 counter drop
' | nft -f -
ipv4_validate </tmp/ip_lists | awk '{print "add element inet filter ipmaster { "$1" }"}' | nft -f - # import ipv4
ipv6_validate </tmp/ip_lists | awk '{print "add element inet filter ipmaster6 { "$1" }"}' | nft -f - # import ipv6

Creare regula conectare vpn wireguard (nativa)

[[ -n $wg_file ]] && file=$wg_file || file=$opt_file; ! [[ -s $file ]] && return 1; iname=$(basename -s .conf $file) address=$(grep '^Address' $file | ipv4_validate) address6=$(grep '^Address' $file | ipv6_validate)
ip link add $iname type wireguard || return 1; wg setconf $iname <(grep -E '^\[Interface|^\[Peer|^PrivateKey|^PublicKey|^Endpoint|^AllowedIPs|^$' $file) || return 1
ip -4 address add $address dev $iname; ip -6 address add $address6 dev $iname
grep '^DNS' $file | sed 's/DNS =/nameserver/' | resolvconf -a tun."$iname" -m 0 -x
wg set $iname fwmark 51820
ip link set mtu 1420 up dev $iname
sysctl -q net.ipv4.conf.all.src_valid_mark=1
ip -4 route add 0.0.0.0/0 dev $iname table 51820; ip -6 route add ::/0 dev $iname table 51820
for cmd in 'ip -4' 'ip -6'; do $cmd rule add not fwmark 51820 table 51820; $cmd rule add table main suppress_prefixlength 0; done
echo '
add table inet fw
add chain inet fw INPUT { type filter hook input priority 0 ; }
add chain inet fw preraw { type filter hook prerouting priority -300; }
add rule inet fw preraw iifname != '$iname' ip daddr '$(cut -d/ -f1 <<<$address)' fib saddr type != local drop
add rule inet fw preraw iifname != '$iname' ip6 daddr '$(cut -d/ -f1 <<<$address6)' fib saddr type != local drop
add chain inet fw premangle { type filter hook prerouting priority -150; }
add rule inet fw premangle meta l4proto udp meta mark set ct mark
add chain inet fw postmangle { type filter hook postrouting priority -150; }
add rule inet fw postmangle meta l4proto udp mark 51820 ct mark set mark
' | nft -f - && echo $iname connected

iptables

Exemplu 1

# iptables-save > /dev/stdout
# Warning: iptables-legacy tables present, use iptables-legacy-save to see them
# iptables-legacy-save > /dev/stdout
# Generated by iptables-save v1.8.9 on Mon Nov 11 14:43:17 2024
*mangle
:PREROUTING ACCEPT [192:15752]
:INPUT ACCEPT [192:15752]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [192:15752]
:POSTROUTING ACCEPT [192:15752]
COMMIT
# Completed on Mon Nov 11 14:43:17 2024
# Generated by iptables-save v1.8.9 on Mon Nov 11 14:43:17 2024
*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [50:3402]
:POSTROUTING ACCEPT [50:3402]
COMMIT
# Completed on Mon Nov 11 14:43:17 2024
# Generated by iptables-save v1.8.9 on Mon Nov 11 14:43:17 2024
*filter
:INPUT DROP [0:0]
:FORWARD DROP [0:0]
:OUTPUT DROP [0:0]
:bad_packets - [0:0]
:bad_tcp_packets - [0:0]
:icmp_packets - [0:0]
:tcp_inbound - [0:0]
:tcp_outbound - [0:0]
:udp_inbound - [0:0]
:udp_outbound - [0:0]
-A INPUT -i lo -j ACCEPT
-A INPUT -j bad_packets
-A INPUT -d 224.0.0.1/32 -j DROP
-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -j tcp_inbound
-A INPUT -p udp -j udp_inbound
-A INPUT -p icmp -j icmp_packets
-A INPUT -m pkttype --pkt-type broadcast -j DROP
-A INPUT -m limit --limit 3/min --limit-burst 3 -j LOG --log-prefix "INPUT packet died: "
-A OUTPUT -p icmp -m conntrack --ctstate INVALID -j DROP
-A OUTPUT -s 127.0.0.1/32 -j ACCEPT
-A OUTPUT -o lo -j ACCEPT
-A OUTPUT -j ACCEPT
-A OUTPUT -m limit --limit 3/min --limit-burst 3 -j LOG --log-prefix "OUTPUT packet died: "
-A bad_packets -m conntrack --ctstate INVALID -j LOG --log-prefix "Invalid packet: "
-A bad_packets -m conntrack --ctstate INVALID -j DROP
-A bad_packets -p tcp -j bad_tcp_packets
-A bad_packets -j RETURN
-A bad_tcp_packets -p tcp -m tcp ! --tcp-flags FIN,SYN,RST,ACK SYN -m conntrack --ctstate NEW -j LOG --log-prefix "New not syn: "
-A bad_tcp_packets -p tcp -m tcp ! --tcp-flags FIN,SYN,RST,ACK SYN -m conntrack --ctstate NEW -j DROP
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j LOG --log-prefix "Stealth scan: "
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,RST,PSH,ACK,URG -j LOG --log-prefix "Stealth scan: "
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,RST,PSH,ACK,URG -j DROP
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,PSH,URG -j LOG --log-prefix "Stealth scan: "
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,PSH,URG -j DROP
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,RST,ACK,URG -j LOG --log-prefix "Stealth scan: "
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,RST,ACK,URG -j DROP
-A bad_tcp_packets -p tcp -m tcp --tcp-flags SYN,RST SYN,RST -j LOG --log-prefix "Stealth scan: "
-A bad_tcp_packets -p tcp -m tcp --tcp-flags SYN,RST SYN,RST -j DROP
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN FIN,SYN -j LOG --log-prefix "Stealth scan: "
-A bad_tcp_packets -p tcp -m tcp --tcp-flags FIN,SYN FIN,SYN -j DROP
-A bad_tcp_packets -p tcp -j RETURN
-A icmp_packets -p icmp -f -j LOG --log-prefix "ICMP Fragment: "
-A icmp_packets -p icmp -f -j DROP
-A icmp_packets -p icmp -m icmp --icmp-type 8 -j DROP
-A icmp_packets -p icmp -m icmp --icmp-type 11 -j ACCEPT
-A icmp_packets -p icmp -j RETURN
-A tcp_inbound -p tcp -m tcp --dport 21 -j ACCEPT
-A tcp_inbound -p tcp -m tcp --sport 20 -j ACCEPT
-A tcp_inbound -p tcp -m tcp --dport 22 -j ACCEPT
-A tcp_inbound -p tcp -m tcp --dport 631 -j ACCEPT
-A tcp_inbound -p tcp -j RETURN
-A tcp_outbound -p tcp -j ACCEPT
-A udp_inbound -p udp -m udp --sport 67 --dport 68 -j ACCEPT
-A udp_inbound -p udp -m udp --dport 631 -j ACCEPT
-A udp_inbound -p udp -m udp --sport 68 --dport 67 -j ACCEPT
-A udp_inbound -p udp -m udp --sport 67 --dport 68 -j ACCEPT
-A udp_inbound -p udp -m udp --dport 111 -j ACCEPT
-A udp_inbound -p udp -m udp --dport 9400 -j ACCEPT
-A udp_inbound -p udp -m udp --dport 2049 -j ACCEPT
-A udp_inbound -p udp -m udp --dport 9401 -j ACCEPT
-A udp_inbound -p udp -m udp --dport 9402 -j ACCEPT
-A udp_inbound -p udp -m udp --dport 9403 -j ACCEPT
-A udp_inbound -p udp -j RETURN
-A udp_outbound -p udp -j ACCEPT
COMMIT
# Completed on Mon Nov 11 14:43:17 2024

Ceea ce se traduce in:

iptables -L
Chain INPUT (policy DROP)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             anywhere            
bad_packets  all  --  anywhere             anywhere            
DROP       all  --  anywhere             224.0.0.1           
ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
tcp_inbound  tcp  --  anywhere             anywhere            
udp_inbound  udp  --  anywhere             anywhere            
icmp_packets  icmp --  anywhere             anywhere            
DROP       all  --  anywhere             anywhere             PKTTYPE = broadcast
LOG        all  --  anywhere             anywhere             limit: avg 3/min burst 3 LOG level warn prefix "INPUT packet died: "

Chain FORWARD (policy DROP)
target     prot opt source               destination         

Chain OUTPUT (policy DROP)
target     prot opt source               destination         
DROP       icmp --  anywhere             anywhere             ctstate INVALID
ACCEPT     all  --  localhost            anywhere            
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere            
LOG        all  --  anywhere             anywhere             limit: avg 3/min burst 3 LOG level warn prefix "OUTPUT packet died: "

Chain bad_packets (1 references)
target     prot opt source               destination         
LOG        all  --  anywhere             anywhere             ctstate INVALID LOG level warn prefix "Invalid packet: "
DROP       all  --  anywhere             anywhere             ctstate INVALID
bad_tcp_packets  tcp  --  anywhere             anywhere            
RETURN     all  --  anywhere             anywhere            

Chain bad_tcp_packets (1 references)
target     prot opt source               destination         
LOG        tcp  --  anywhere             anywhere             tcp flags:!FIN,SYN,RST,ACK/SYN ctstate NEW LOG level warn prefix "New not syn: "
DROP       tcp  --  anywhere             anywhere             tcp flags:!FIN,SYN,RST,ACK/SYN ctstate NEW
LOG        tcp  --  anywhere             anywhere             tcp flags:FIN,SYN,RST,PSH,ACK,URG/NONE LOG level warn prefix "Stealth scan: "
DROP       tcp  --  anywhere             anywhere             tcp flags:FIN,SYN,RST,PSH,ACK,URG/NONE
LOG        tcp  --  anywhere             anywhere             tcp flags:FIN,SYN,RST,PSH,ACK,URG/FIN,SYN,RST,PSH,ACK,URG LOG level warn prefix "Stealth scan: "
DROP       tcp  --  anywhere             anywhere             tcp flags:FIN,SYN,RST,PSH,ACK,URG/FIN,SYN,RST,PSH,ACK,URG
LOG        tcp  --  anywhere             anywhere             tcp flags:FIN,SYN,RST,PSH,ACK,URG/FIN,PSH,URG LOG level warn prefix "Stealth scan: "
DROP       tcp  --  anywhere             anywhere             tcp flags:FIN,SYN,RST,PSH,ACK,URG/FIN,PSH,URG
LOG        tcp  --  anywhere             anywhere             tcp flags:FIN,SYN,RST,PSH,ACK,URG/FIN,SYN,RST,ACK,URG LOG level warn prefix "Stealth scan: "
DROP       tcp  --  anywhere             anywhere             tcp flags:FIN,SYN,RST,PSH,ACK,URG/FIN,SYN,RST,ACK,URG
LOG        tcp  --  anywhere             anywhere             tcp flags:SYN,RST/SYN,RST LOG level warn prefix "Stealth scan: "
DROP       tcp  --  anywhere             anywhere             tcp flags:SYN,RST/SYN,RST
LOG        tcp  --  anywhere             anywhere             tcp flags:FIN,SYN/FIN,SYN LOG level warn prefix "Stealth scan: "
DROP       tcp  --  anywhere             anywhere             tcp flags:FIN,SYN/FIN,SYN
RETURN     tcp  --  anywhere             anywhere            

Chain icmp_packets (1 references)
target     prot opt source               destination         
LOG        icmp -f  anywhere             anywhere             LOG level warn prefix "ICMP Fragment: "
DROP       icmp -f  anywhere             anywhere            
DROP       icmp --  anywhere             anywhere             icmp echo-request
ACCEPT     icmp --  anywhere             anywhere             icmp time-exceeded
RETURN     icmp --  anywhere             anywhere            

Chain tcp_inbound (1 references)
target     prot opt source               destination         
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ftp
ACCEPT     tcp  --  anywhere             anywhere             tcp spt:ftp-data
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ipp
RETURN     tcp  --  anywhere             anywhere            

Chain tcp_outbound (0 references)
target     prot opt source               destination         
ACCEPT     tcp  --  anywhere             anywhere            

Chain udp_inbound (1 references)
target     prot opt source               destination         
ACCEPT     udp  --  anywhere             anywhere             udp spt:bootps dpt:bootpc
ACCEPT     udp  --  anywhere             anywhere             udp dpt:ipp
ACCEPT     udp  --  anywhere             anywhere             udp spt:bootpc dpt:bootps
ACCEPT     udp  --  anywhere             anywhere             udp spt:bootps dpt:bootpc
ACCEPT     udp  --  anywhere             anywhere             udp dpt:sunrpc
ACCEPT     udp  --  anywhere             anywhere             udp dpt:9400
ACCEPT     udp  --  anywhere             anywhere             udp dpt:nfs
ACCEPT     udp  --  anywhere             anywhere             udp dpt:9401
ACCEPT     udp  --  anywhere             anywhere             udp dpt:9402
ACCEPT     udp  --  anywhere             anywhere             udp dpt:9403
RETURN     udp  --  anywhere             anywhere            

Chain udp_outbound (0 references)
target     prot opt source               destination         
ACCEPT     udp  --  anywhere             anywhere  

Exemplu 2

*filter
# Allow all outgoing, but drop incoming and forwarding packets by default
:INPUT DROP [0:0]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [0:0]

# Custom per-protocol chains
:UDP - [0:0]
:TCP - [0:0]
:ICMP - [0:0]

# Acceptable UDP traffic

# Acceptable TCP traffic
-A TCP -p tcp --dport 22 -j ACCEPT

# Acceptable ICMP traffic

# Boilerplate acceptance policy
-A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
-A INPUT -i lo -j ACCEPT

# Drop invalid packets
-A INPUT -m conntrack --ctstate INVALID -j DROP

# Pass traffic to protocol-specific chains
## Only allow new connections (established and related should already be handled)
## For TCP, additionally only allow new SYN packets since that is the only valid
## method for establishing a new TCP connection
-A INPUT -p udp -m conntrack --ctstate NEW -j UDP
-A INPUT -p tcp --syn -m conntrack --ctstate NEW -j TCP
-A INPUT -p icmp -m conntrack --ctstate NEW -j ICMP

# Reject anything that's fallen through to this point
## Try to be protocol-specific w/ rejection message
-A INPUT -p udp -j REJECT --reject-with icmp-port-unreachable
-A INPUT -p tcp -j REJECT --reject-with tcp-reset
-A INPUT -j REJECT --reject-with icmp-proto-unreachable

# Commit the changes
COMMIT

*raw
:PREROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
COMMIT

*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
COMMIT

*security
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
COMMIT

*mangle
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
COMMIT

Creare regula blocare ip-uri (folosind ipset)

ipv4_validate </tmp/ip_lists | awk 'NR==1{print "create ipmaster hash:net family inet hashsize 100000 maxelem 100000"}''{print "add ipmaster "$1}' | ipset restore -!
iptables -I INPUT -m set --match-set ipmaster src -j DROP || ierr=1 # import ipv4
ipv6_validate </tmp/ip_lists | awk 'NR==1{print "create ipmaster6 hash:net family inet6 hashsize 500000 maxelem 500000"}''{print "add ipmaster6 "$1}' | ipset restore -!
ip6tables -I INPUT -m set --match-set ipmaster6 src -j DROP || ierr=1 # import ipv6

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