[Quick Tips] : How to protect from port scanning and smurf attack in Linux Server by iptables

How to protect from port scanning and smurf attack in Linux Server by iptables

In this post I will share the iptable script in which we will learn How to protect from port scanning and smurf attack in Linux Server.

Features Of Script :

(1) When a attacker try to port scan your server, first because of iptable attacker will not get any information which port is open. Second the Attacking IP address will be blacklisted for 24 Hour (You can change it in script) . Third , after that attacker will not able to open access anything for eg. even attacker will not see any website running on server via web browser, not able to ssh,telnet also. Means completely restricted.

(2) Protects from smurf attack

(3) Written with the help of IPTABLE hence no System Performance issue like CPU high,Memory usage etc. No third party tool is used

Note: You can add or remove port no. as per your requirement.

Description about Server where we will implement IPTABLE script:

Operating Syetem : CentOS 6.4 (applicable to Red hat and CentOS servers)
IP Address: 192.168.1.4

Now we will create the script

Step 1: Create a bash script with the name of iptablescript.sh

1	vi /root/iptablescript.sh

Step 2: Now paste the below given script contents in your bash script file iptablescript.sh

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#!/bin/sh # # # Script is for stoping Portscan and smurf attack   ### first flush all the iptables Rules iptables -F     # INPUT iptables Rules # Accept loopback input iptables -A INPUT -i lo -p all -j ACCEPT   # allow 3 way handshake iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT   ### DROPspoofing packets iptables -A INPUT -s 10.0.0.0/8 -j DROP iptables -A INPUT -s 169.254.0.0/16 -j DROP iptables -A INPUT -s 172.16.0.0/12 -j DROP iptables -A INPUT -s 127.0.0.0/8 -j DROP iptables -A INPUT -s 192.168.0.0/24 -j DROP   iptables -A INPUT -s 224.0.0.0/4 -j DROP iptables -A INPUT -d 224.0.0.0/4 -j DROP iptables -A INPUT -s 240.0.0.0/5 -j DROP iptables -A INPUT -d 240.0.0.0/5 -j DROP iptables -A INPUT -s 0.0.0.0/8 -j DROP iptables -A INPUT -d 0.0.0.0/8 -j DROP iptables -A INPUT -d 239.255.255.0/24 -j DROP iptables -A INPUT -d 255.255.255.255 -j DROP   #for SMURF attack protection iptables -A INPUT -p icmp -m icmp --icmp-type address-mask-request -j DROP iptables -A INPUT -p icmp -m icmp --icmp-type timestamp-request -j DROP iptables -A INPUT -p icmp -m icmp -m limit --limit 1/second -j ACCEPT   # Droping all invalid packets iptables -A INPUT -m state --state INVALID -j DROP iptables -A FORWARD -m state --state INVALID -j DROP iptables -A OUTPUT -m state --state INVALID -j DROP   # flooding of RST packets, smurf attack Rejection iptables -A INPUT -p tcp -m tcp --tcp-flags RST RST -m limit --limit 2/second --limit-burst 2 -j ACCEPT   # Protecting portscans # Attacking IP will be locked for 24 hours (3600 x 24 = 86400 Seconds) iptables -A INPUT -m recent --name portscan --rcheck --seconds 86400 -j DROP iptables -A FORWARD -m recent --name portscan --rcheck --seconds 86400 -j DROP   # Remove attacking IP after 24 hours iptables -A INPUT -m recent --name portscan --remove iptables -A FORWARD -m recent --name portscan --remove   # These rules add scanners to the portscan list, and log the attempt. iptables -A INPUT -p tcp -m tcp --dport 139 -m recent --name portscan --set -j LOG --log-prefix "portscan:" iptables -A INPUT -p tcp -m tcp --dport 139 -m recent --name portscan --set -j DROP   iptables -A FORWARD -p tcp -m tcp --dport 139 -m recent --name portscan --set -j LOG --log-prefix "portscan:" iptables -A FORWARD -p tcp -m tcp --dport 139 -m recent --name portscan --set -j DROP   # Allow the following ports through from outside iptables -A INPUT -p tcp -m tcp --dport 25 -j ACCEPT iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT iptables -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT   # Allow ping means ICMP port is open (If you do not want ping replace ACCEPT with REJECT) iptables -A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT   # Lastly reject All INPUT traffic iptables -A INPUT -j REJECT     ################# Below are for OUTPUT iptables rules #############################################   ## Allow loopback OUTPUT iptables -A OUTPUT -o lo -j ACCEPT iptables -A OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT   # Allow the following ports through from outside # SMTP = 25 # DNS =53 # HTTP = 80 # HTTPS = 443 # SSH = 22 ### You can also add or remove port no. as per your requirement   iptables -A OUTPUT -p tcp -m tcp --dport 25 -j ACCEPT iptables -A OUTPUT -p udp -m udp --dport 53 -j ACCEPT iptables -A OUTPUT -p tcp -m tcp --dport 80 -j ACCEPT iptables -A OUTPUT -p tcp -m tcp --dport 443 -j ACCEPT iptables -A OUTPUT -p tcp -m tcp --dport 22 -j ACCEPT   # Allow pings iptables -A OUTPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT   # Lastly Reject all Output traffic iptables -A OUTPUT -j REJECT   ## Reject Forwarding  traffic iptables -A FORWARD -j REJECT

Step 3: Make the Read Write Execute permission only to root user. (For security)

1 2	chmod 700 /root/iptablescript.sh   chown root:root /root/iptablescript.sh

Step 4 : Now run the script

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sh /root/iptablescript.sh   or   ./root/iptablescript.sh

Step 6: Now check the IPTABLES rule with following command

1	iptables -nL

Now we will do testing from remote server to our server where we have implemented the iptable

Step 7: login into any system and try to do port scanning

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nmap -sT Server-ip-address   eg.   nmap -sT 192.168.1.4

Step 8: The result should be now from your system like following types

(a) Not getting any output from nmap
(b) Not able to do telnet to any port for eg. telnet Server-ip-address 22

After running nmap means port scan your ip-address is blacklisted.

You can find your system ip address in message logs in Server with the keyword called portscan.
So login back to your server and check the messages log in /var/log

Note : how to install nmap

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In Red Hat and CentOS   yum install nmap   In Debian and Ubuntu   apt-get install nmap