Pejman Moghadam / General

iptables recent module usage by example

Statistics : /proc/net/ipt_recent

Public domain

---

icmp check: 2 packets per 10 seconds - rcheck

iptables -F
iptables -A INPUT -p icmp --icmp-type echo-request -m recent --rcheck --seconds 10 --hitcount 2 --name ICMPCHECK -j DROP
iptables -A INPUT -p icmp --icmp-type echo-request -m recent --set --name ICMPCHECK -j ACCEPT

---

icmp check: 2 packets per 10 seconds - update

iptables -F
iptables -A INPUT -p icmp --icmp-type echo-request -m recent --update --seconds 10 --hitcount 2 --name ICMPCHECK -j DROP
iptables -A INPUT -p icmp --icmp-type echo-request -m recent --set --name ICMPCHECK -j ACCEPT

---

SSH brute-force prevention : 3 connections per 60 seconds

SSHPORT=22
iptables -F
iptables -A INPUT -p tcp --dport ${SSHPORT} -m state --state NEW -m recent --update --seconds 60 --hitcount 3 --name BRUTEFORCE -j DROP 
iptables -A INPUT -p tcp --dport ${SSHPORT} -m state --state NEW -m recent --set --name BRUTEFORCE -j ACCEPT

---

SSH brute-force prevention : 3 connections per 60 seconds - separate chain

SSHPORT=22
iptables -F
iptables -X
iptables -N BRUTECHECK
iptables -A INPUT -p tcp --dport ${SSHPORT} -m state --state NEW -j BRUTECHECK
iptables -A BRUTECHECK -m recent --update --seconds 60 --hitcount 3 --name BRUTEFORCE -j DROP
iptables -A BRUTECHECK -m recent --set --name BRUTEFORCE -j ACCEPT

---

SSH port knocking : tcp/1000 , tcp/2000

SSHPORT=22
N1=1000
N2=2000
iptables -F
iptables -X
iptables -N KNOCK1
iptables -N KNOCK2
iptables -N OK

iptables -A KNOCK1 -m recent --set --name SEENFIRST
iptables -A KNOCK1 -m recent --remove --name KNOCKED
iptables -A KNOCK1 -j DROP

iptables -A KNOCK2 -m recent --rcheck --name SEENFIRST --seconds 5 -j OK
iptables -A KNOCK2 -m recent --remove --name SEENFIRST
iptables -A KNOCK2 -j DROP

iptables -A OK -m recent --set --name KNOCKED
iptables -A OK -j DROP

iptables -A INPUT -p tcp --dport ${N1} -j KNOCK1
iptables -A INPUT -p tcp --dport ${N2} -j KNOCK2
iptables -A INPUT -p tcp --dport ${SSHPORT} -m state --state NEW -m recent --seconds 10 --rcheck --name KNOCKED -j ACCEPT
iptables -A INPUT -p tcp --dport ${SSHPORT} -m state --state NEW -j DROP

---

SSH port knocker script

#!/bin/bash
HOST="172.16.20.2"
SSHPORT=22
KNOCKS="1000 2000"

for PORT in $KNOCKS; do
  echo "Knock: $PORT"
  telnet $HOST $PORT &> /dev/null &
  P=$(echo $!)
  echo "PID: ${P}"
  sleep 1
  kill -KILL ${P}
done
ssh -p${SSHPORT} ${HOST}

---

BY: Pejman Moghadam
TAG: ssh, port-knocking, recent, iptables, firewall
DATE: 2011-03-04 22:24:41

---

Pejman Moghadam / General [ TXT ]