No Ubuntu 16.04, instalei o ufw e o configurei para que ele tenha o seguinte status ( sudo ufw status verbose ):
Status: active
Logging: on (full)
Default: deny (incoming), allow (outgoing), deny (routed)
New profiles: skip
To Action From
-- ------ ----
80,443/tcp (Nginx Full) ALLOW IN Anywhere
995/tcp (Dovecot Secure POP3) ALLOW IN Anywhere
993/tcp (Dovecot Secure IMAP) ALLOW IN Anywhere
22/tcp (OpenSSH) ALLOW IN Anywhere
25/tcp (Postfix) ALLOW IN Anywhere
465/tcp (Postfix SMTPS) ALLOW IN Anywhere
9522/tcp (hinext) ALLOW IN Anywhere
9522,9523/tcp (hinext) ALLOW IN Anywhere
9524/tcp (test) ALLOW IN Anywhere
9522/tcp (hinext (v6)) ALLOW IN Anywhere (v6)
9522,9523/tcp (hinext (v6)) ALLOW IN Anywhere (v6)
9524/tcp (test (v6)) ALLOW IN Anywhere (v6)
Como pode ser visto, a porta 8822 NÃO está na lista e, portanto, deve ser bloqueada pela política padrão (que é deny para a cadeia incoming ).
MAS: consigo abrir uma conexão SSH para a porta 8822 do mundo externo para o meu servidor SSH ouvindo nas portas 22 e 8822.
Por que o tráfego para a porta 8822 pode atravessar o firewall ufw sem ser descartado?
Para mais informações de diagnóstico, iptables-save -c diz isto:
# Generated by iptables-save v1.6.0 on Tue Apr 24 23:55:19 2018
*raw
:PREROUTING ACCEPT [622500:111511726]
:OUTPUT ACCEPT [631989:135819596]
COMMIT
# Completed on Tue Apr 24 23:55:19 2018
# Generated by iptables-save v1.6.0 on Tue Apr 24 23:55:19 2018
*mangle
:PREROUTING ACCEPT [622500:111511726]
:INPUT ACCEPT [622500:111511726]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [631989:135819596]
:POSTROUTING ACCEPT [631989:135819596]
COMMIT
# Completed on Tue Apr 24 23:55:19 2018
# Generated by iptables-save v1.6.0 on Tue Apr 24 23:55:19 2018
*nat
:PREROUTING ACCEPT [46994:2923568]
:POSTROUTING ACCEPT [7607:511281]
:OUTPUT ACCEPT [7607:511281]
COMMIT
# Completed on Tue Apr 24 23:55:19 2018
# Generated by iptables-save v1.6.0 on Tue Apr 24 23:55:19 2018
*filter
:INPUT ACCEPT [63:5355]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:VZ_FORWARD - [0:0]
:VZ_INPUT - [0:0]
:VZ_OUTPUT - [0:0]
:ufw-after-forward - [0:0]
:ufw-after-input - [0:0]
:ufw-after-logging-forward - [0:0]
:ufw-after-logging-input - [0:0]
:ufw-after-logging-output - [0:0]
:ufw-after-output - [0:0]
:ufw-before-forward - [0:0]
:ufw-before-input - [0:0]
:ufw-before-logging-forward - [0:0]
:ufw-before-logging-input - [0:0]
:ufw-before-logging-output - [0:0]
:ufw-before-output - [0:0]
:ufw-logging-allow - [0:0]
:ufw-logging-deny - [0:0]
:ufw-not-local - [0:0]
:ufw-reject-forward - [0:0]
:ufw-reject-input - [0:0]
:ufw-reject-output - [0:0]
:ufw-skip-to-policy-forward - [0:0]
:ufw-skip-to-policy-input - [0:0]
:ufw-skip-to-policy-output - [0:0]
:ufw-track-forward - [0:0]
:ufw-track-input - [0:0]
:ufw-track-output - [0:0]
:ufw-user-forward - [0:0]
:ufw-user-input - [0:0]
:ufw-user-limit - [0:0]
:ufw-user-limit-accept - [0:0]
:ufw-user-logging-forward - [0:0]
:ufw-user-logging-input - [0:0]
:ufw-user-logging-output - [0:0]
:ufw-user-output - [0:0]
[622500:111511726] -A INPUT -j VZ_INPUT
[491972:96179570] -A INPUT -j ufw-before-logging-input
[491972:96179570] -A INPUT -j ufw-before-input
[21445:1425920] -A INPUT -j ufw-after-input
[17022:1199401] -A INPUT -j ufw-after-logging-input
[17022:1199401] -A INPUT -j ufw-reject-input
[17022:1199401] -A INPUT -j ufw-track-input
[0:0] -A FORWARD -j VZ_FORWARD
[0:0] -A FORWARD -j ufw-before-logging-forward
[0:0] -A FORWARD -j ufw-before-forward
[0:0] -A FORWARD -j ufw-after-forward
[0:0] -A FORWARD -j ufw-after-logging-forward
[0:0] -A FORWARD -j ufw-reject-forward
[0:0] -A FORWARD -j ufw-track-forward
[631989:135819596] -A OUTPUT -j VZ_OUTPUT
[478124:111192792] -A OUTPUT -j ufw-before-logging-output
[478124:111192792] -A OUTPUT -j ufw-before-output
[4466:322671] -A OUTPUT -j ufw-after-output
[4466:322671] -A OUTPUT -j ufw-after-logging-output
[4466:322671] -A OUTPUT -j ufw-reject-output
[4466:322671] -A OUTPUT -j ufw-track-output
[23:1823] -A VZ_INPUT -p tcp -m tcp --dport 80 -j ACCEPT
[5136:565736] -A VZ_INPUT -p tcp -m tcp --dport 22 -j ACCEPT
[4:172] -A VZ_INPUT -p tcp -m tcp --dport 25 -j ACCEPT
[4:172] -A VZ_INPUT -p tcp -m tcp --dport 110 -j ACCEPT
[6:304] -A VZ_INPUT -p tcp -m tcp --dport 53 -j ACCEPT
[2:115] -A VZ_INPUT -p udp -m udp --dport 53 -j ACCEPT
[410:19580] -A VZ_INPUT -p tcp -m tcp --dport 32768:65535 -j ACCEPT
[39:3651] -A VZ_INPUT -p udp -m udp --dport 32768:65535 -j ACCEPT
[1:44] -A VZ_INPUT -p tcp -m tcp --dport 8880 -j ACCEPT
[3:152] -A VZ_INPUT -p tcp -m tcp --dport 8443 -j ACCEPT
[8:470] -A VZ_INPUT -s 127.0.0.1/32 -d 127.0.0.1/32 -p tcp -j ACCEPT
[0:0] -A VZ_INPUT -s 127.0.0.1/32 -d 127.0.0.1/32 -p udp -j ACCEPT
[17:2105] -A VZ_OUTPUT -p tcp -m tcp --sport 80 -j ACCEPT
[4940:995587] -A VZ_OUTPUT -p tcp -m tcp --sport 22 -j ACCEPT
[4:214] -A VZ_OUTPUT -p tcp -m tcp --sport 25 -j ACCEPT
[4:192] -A VZ_OUTPUT -p tcp -m tcp --sport 110 -j ACCEPT
[6:240] -A VZ_OUTPUT -p tcp -m tcp --sport 53 -j ACCEPT
[0:0] -A VZ_OUTPUT -p udp -m udp --sport 53 -j ACCEPT
[3888:279384] -A VZ_OUTPUT -p tcp -j ACCEPT
[39:2831] -A VZ_OUTPUT -p udp -j ACCEPT
[0:0] -A VZ_OUTPUT -p tcp -m tcp --sport 8880 -j ACCEPT
[0:0] -A VZ_OUTPUT -p tcp -m tcp --sport 8443 -j ACCEPT
[0:0] -A VZ_OUTPUT -s 127.0.0.1/32 -d 127.0.0.1/32 -p tcp -j ACCEPT
[0:0] -A VZ_OUTPUT -s 127.0.0.1/32 -d 127.0.0.1/32 -p udp -j ACCEPT
[5:391] -A ufw-after-input -p udp -m udp --dport 137 -j ufw-skip-to-policy-input
[0:0] -A ufw-after-input -p udp -m udp --dport 138 -j ufw-skip-to-policy-input
[16:700] -A ufw-after-input -p tcp -m tcp --dport 139 -j ufw-skip-to-policy-input
[1936:99244] -A ufw-after-input -p tcp -m tcp --dport 445 -j ufw-skip-to-policy-input
[0:0] -A ufw-after-input -p udp -m udp --dport 67 -j ufw-skip-to-policy-input
[0:0] -A ufw-after-input -p udp -m udp --dport 68 -j ufw-skip-to-policy-input
[0:0] -A ufw-after-input -m addrtype --dst-type BROADCAST -j ufw-skip-to-policy-input
[0:0] -A ufw-after-logging-forward -j LOG --log-prefix "[UFW BLOCK] "
[63:5355] -A ufw-after-logging-input -j LOG --log-prefix "[UFW BLOCK] "
[0:0] -A ufw-after-logging-output -j LOG --log-prefix "[UFW ALLOW] "
[0:0] -A ufw-before-forward -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
[0:0] -A ufw-before-forward -p icmp -m icmp --icmp-type 3 -j ACCEPT
[0:0] -A ufw-before-forward -p icmp -m icmp --icmp-type 4 -j ACCEPT
[0:0] -A ufw-before-forward -p icmp -m icmp --icmp-type 11 -j ACCEPT
[0:0] -A ufw-before-forward -p icmp -m icmp --icmp-type 12 -j ACCEPT
[0:0] -A ufw-before-forward -p icmp -m icmp --icmp-type 8 -j ACCEPT
[0:0] -A ufw-before-forward -j ufw-user-forward
[10789:9641505] -A ufw-before-input -i lo -j ACCEPT
[252164:53646696] -A ufw-before-input -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
[3048:131944] -A ufw-before-input -m conntrack --ctstate INVALID -j ufw-logging-deny
[3048:131944] -A ufw-before-input -m conntrack --ctstate INVALID -j DROP
[0:0] -A ufw-before-input -p icmp -m icmp --icmp-type 3 -j ACCEPT
[0:0] -A ufw-before-input -p icmp -m icmp --icmp-type 4 -j ACCEPT
[0:0] -A ufw-before-input -p icmp -m icmp --icmp-type 11 -j ACCEPT
[0:0] -A ufw-before-input -p icmp -m icmp --icmp-type 12 -j ACCEPT
[21:952] -A ufw-before-input -p icmp -m icmp --icmp-type 8 -j ACCEPT
[0:0] -A ufw-before-input -p udp -m udp --sport 67 --dport 68 -j ACCEPT
[22062:1348553] -A ufw-before-input -j ufw-not-local
[0:0] -A ufw-before-input -d 224.0.0.251/32 -p udp -m udp --dport 5353 -j ACCEPT
[0:0] -A ufw-before-input -d 239.255.255.250/32 -p udp -m udp --dport 1900 -j ACCEPT
[22062:1348553] -A ufw-before-input -j ufw-user-input
[0:0] -A ufw-before-logging-forward -j LOG --log-prefix "[UFW AUDIT] "
[327:39433] -A ufw-before-logging-input -j LOG --log-prefix "[UFW AUDIT] "
[10:3444] -A ufw-before-logging-output -j LOG --log-prefix "[UFW AUDIT] "
[10789:9641505] -A ufw-before-output -o lo -j ACCEPT
[277561:60253281] -A ufw-before-output -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
[1888:133952] -A ufw-before-output -j ufw-user-output
[0:0] -A ufw-logging-allow -j LOG --log-prefix "[UFW ALLOW] "
[29:1244] -A ufw-logging-deny -m conntrack --ctstate INVALID -j LOG --log-prefix "[UFW AUDIT INVALID] "
[29:1244] -A ufw-logging-deny -j LOG --log-prefix "[UFW BLOCK] "
[22062:1348553] -A ufw-not-local -m addrtype --dst-type LOCAL -j RETURN
[0:0] -A ufw-not-local -m addrtype --dst-type MULTICAST -j RETURN
[0:0] -A ufw-not-local -m addrtype --dst-type BROADCAST -j RETURN
[0:0] -A ufw-not-local -m limit --limit 3/min --limit-burst 10 -j ufw-logging-deny
[0:0] -A ufw-not-local -j DROP
[0:0] -A ufw-skip-to-policy-forward -j DROP
[1957:100335] -A ufw-skip-to-policy-input -j DROP
[0:0] -A ufw-skip-to-policy-output -j ACCEPT
[1:60] -A ufw-track-output -p tcp -m conntrack --ctstate NEW -j ACCEPT
[1746:126492] -A ufw-track-output -p udp -m conntrack --ctstate NEW -j ACCEPT
[526:29104] -A ufw-user-input -p tcp -m multiport --dports 80,443 -m comment --comment "\'dapp_Nginx%20Full\'" -j ACCEPT
[76:3832] -A ufw-user-input -p tcp -m tcp --dport 995 -m comment --comment "\'dapp_Dovecot%20Secure%20POP3\'" -j ACCEPT
[8:372] -A ufw-user-input -p tcp -m tcp --dport 993 -m comment --comment "\'dapp_Dovecot%20Secure%20IMAP\'" -j ACCEPT
[9724:581800] -A ufw-user-input -p tcp -m tcp --dport 22 -m comment --comment "\'dapp_OpenSSH\'" -j ACCEPT
[61:3500] -A ufw-user-input -p tcp -m tcp --dport 25 -m comment --comment "\'dapp_Postfix\'" -j ACCEPT
[10:456] -A ufw-user-input -p tcp -m tcp --dport 465 -m comment --comment "\'dapp_Postfix%20SMTPS\'" -j ACCEPT
[0:0] -A ufw-user-input -p tcp -m tcp --dport 9522 -m comment --comment "\'dapp_hinext\'" -j ACCEPT
[1:52] -A ufw-user-input -p tcp -m multiport --dports 9522,9523 -m comment --comment "\'dapp_hinext\'" -j ACCEPT
[5:256] -A ufw-user-input -p tcp -m tcp --dport 9524 -m comment --comment "\'dapp_test\'" -j ACCEPT
[0:0] -A ufw-user-limit -m limit --limit 3/min -j LOG --log-prefix "[UFW LIMIT BLOCK] "
[0:0] -A ufw-user-limit -j REJECT --reject-with icmp-port-unreachable
[0:0] -A ufw-user-limit-accept -j ACCEPT
COMMIT
# Completed on Tue Apr 24 23:55:19 2018
Eu reiniciei o firewall com sudo service ufw restart . Depois disso, a porta 8822 foi bloqueada por usw - como deveria ser.
Além disso, o iptables-save também me conta a história desejada: veja este excerto:
*filter
:INPUT DROP [6:320]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [0:0]
Observe a política padrão "DROP", enquanto no meu post inicial notei uma política padrão "ACCEPT" que não entendi.
Então, reiniciar o ufw aparentemente resolveu o problema.