• Skip to primary navigation
  • Skip to main content
sharadchhetri

sharadchhetri

Tutorials On Linux, Unix & Open Source

  • Home
  • Linux Commands
  • Resources
    • Learn Linux
  • My WordPress plugins

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

June 15, 2013 by Sharad Chhetri 21 Comments

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

vi /root/iptablescript.sh

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

#!/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)

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

Step 4 : Now run the script

sh /root/iptablescript.sh 

or 

./root/iptablescript.sh

Step 6: Now check the IPTABLES rule with following command


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

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

In Red Hat and CentOS 

yum install nmap

In Debian and Ubuntu

apt-get install nmap

Share this:

  • Twitter
  • Facebook
  • More
  • Print
  • Email
  • LinkedIn
  • Reddit
  • Tumblr
  • Pinterest
  • Pocket
  • Telegram
  • WhatsApp
  • Mastodon

Related posts:

  1. Protect from SSL Drown Attack in AWS ELB, Apache and Nginx
  2. How to backup and restore iptables on Linux systems
  3. Protect from w00tw00t.at.blackhats.romanian.anti-sec
  4. Change the default port number of ssh server
  5. Protect ssh with Google Authenticator on Ubuntu 14.04 LTS
  6. Change telnet server port number on CentOS 7 / RHEL 7
  7. How to backup and restore iptables on CentOS 7 / RHEL 7
  8. Change mysql default port number in linux
  9. rsync over ssh port number on Linux/Unix system
  10. How to change smtp port number 25 in postfix

Filed Under: Linux, Tips And Tricks Tagged With: iptables

Reader Interactions

Comments

  1. John says

    December 15, 2020 at 9:31 am

    i am running Debian 10 and i am getting the following errors:
    – icmp: option “–icmp-type” must be specified

    Try `iptables -h’ or ‘iptables –help’ for more information.

    -Also, i do not have access to Internet (dns requests) while ping to 8.8.8.8 works fine. As a consequence no apt-get update/upgrade/install

    Reply
  2. SySAdmin says

    January 9, 2020 at 4:28 pm

    Blocks only partial and simple smurf attacks, the rest are useless.

    Reply
« Older Comments

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Copyright © 2023 ·
The material in this site cannot be republished either online or offline, without our permission.
Proudly Blogging From Bharat.

  • Contact
  • About Me
  • My WordPress plugins
  • Privacy Policy