knowledge-base/KB/Linux/Desktop/Firewall.md

creation date	tags
2023-04-10	note firewall iptables linux

Change icmp to icmp -j REJECT to not allow ping command.

IPv4

Put into /etc/iptables/iptables.rules. Pay attention to blank line at the end.

*filter
:INPUT DROP [0:0]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [0:0]
:TCP - [0:0]
:UDP - [0:0]

-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m conntrack --ctstate INVALID -j DROP
-A INPUT -p icmp -m icmp --icmp-type 8 -m conntrack --ctstate NEW -j ACCEPT
-A INPUT -p udp -m conntrack --ctstate NEW -j UDP
-A INPUT -p tcp --tcp-flags FIN,SYN,RST,ACK SYN -m conntrack --ctstate NEW -j TCP
-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

Enable iptables.service. Verify result with sudo iptables -S.

Add 4713 (pulseaudio) rule if necessary.

-A INPUT -m state --state NEW -m tcp -p tcp --dport 4713 -j ACCEPT

IPv6

Put into /etc/iptables/ip6tables.rules. Pay attention to blank line at the end.

*filter
:INPUT DROP [0:0]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [0:0]
:TCP - [0:0]
:UDP - [0:0]

-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m conntrack --ctstate INVALID -j DROP
-A INPUT -s fe80::/10 -p ipv6-icmp -j ACCEPT
-A INPUT -p udp --sport 547 --dport 546 -j ACCEPT
-A INPUT -p udp -m conntrack --ctstate NEW -j UDP
-A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -m conntrack --ctstate NEW -j TCP
-A INPUT -p udp -j REJECT --reject-with icmp6-adm-prohibited
-A INPUT -p tcp -j REJECT --reject-with tcp-reset
-A INPUT -j REJECT --reject-with icmp6-adm-prohibited
-A INPUT -p ipv6-icmp -m icmp6 --icmpv6-type 128 -m conntrack --ctstate NEW -j ACCEPT

COMMIT

Enable ip6tables.service. Verify result with sudo ip6tables -S.

Add 4713 (pulseaudio) rule if necessary.

-A INPUT -m state --state NEW -m tcp -p tcp --dport 4713 -j ACCEPT