Databases, Systems & Networks

Source: how-to.ovh

Marre des pays exotiques qui essaient de s’introduire sur le serveur et pourrissent vos logs et font bosser fail2ban ?

Une solution pour bloquer les pays avec lesquels vous n’avez pas de relations. Pour Debian mais sûrement adaptable à d’autres distributions.

# Install GeoIP pour iptables

apt-get install dkms xtables-addons-dkms xtables-addons-common xtables-addons-dkms geoip-database libgeoip1 libtext-csv-xs-perl unzip

# On vérifie que c’est ok

dkms status xtables-addons

# on crée le repertoire

mkdir /usr/share/xt_geoip

# on se déplace dedans

cd /usr/share/xt_geoip/

# on télécharge le fichier

wget http://man.sethuper.com/wp-content/uploads/2013/06/geoip-dl-build.tar.gz

# on le décompresse

tar xvf geoip-dl-build.tar.gz

# on l’exécute

./xt_geoip_dl

# si cela donne un message d’erreur, on fait ceci

/usr/bin/perl -MCPAN -e'install Text::CSV_XS'

# on exécute l’autre fichier

./xt_geoip_build -D . *.csv

# on efface les fichiers inutiles

rm -rf geoip-dl-build.tar.gz

# on teste iptables en bloquant la Chine et la Russie

iptables -A INPUT -m geoip --src-cc CN,RU -j DROP

# on vérifie

iptables -L -v

# ce qui donnera cette ligne indiquant que les pays seront bloqués

DROP all -- anywhere anywhere -m geoip --source-country CN,RU

pour interdire le port 22 à ces pays

iptables -A INPUT -p tcp --dport 22 -m geoip --src-cc CN,RU -j DROP

Source: jeshurun.ca

Anyone who has administered even a moderately high traffic server will have noticed that certain unwelcome traffic such as port scans and probes tend to come from IP addresses belonging to a certain group of countries. If your application or service does not cater to users in these countries, it might be a safe bet to block these countries off entirely.

This is especially true for email servers. The average email server, based on anecdotal evidence of servers for around 20 domains, rejects about 30% of incoming email every day as spam. Some servers on some days reject up to as much as 97% of incoming email as spam. Most of these originate in a certain subset of countries. That is a lot of wasted CPU cycles being expended on scanning these undesired emails for spam and viruses. Although tools such as amavisd and spamassasin do a good job of keeping the vast majority of spam out of users’ inboxes, when the rare well crafted and targeted phishing email does get through, it wrecks havoc in the enterprise.

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If you read our previous article Easy Ubuntu Server Firewall, then you may have noted that on Ubuntu 16.04 the described method no longer works. This is due to systemd. In the article below we will walk through creating a persistent IPTables based firewall on Ubuntu 16.04 LTS. First we need to install some required software packages. As seen in the command below, install iptables-persistent. Next we will make netfilter-persistent run at boot. This is the most important step as it will ensure your rules are reloaded at boot time.

# Install IPTables Persistent Package
apt-get install -y iptables-persistent
# Add netfilter-persistent Startup
invoke-rc.d netfilter-persistent save
# Stop netfilter-persistent Service
service netfilter-persistent stop

Once the packages above are installed and the service is stopped, you will have a new directory at /etc/iptables/. This directory holds the IPTables filter rules that will be reloaded at boot time. These files are named rules.v4 and rules.v6 respectively. IPV4 rules are loaded into rules.v4 and IPV6 rules are loaded into rules.v6. For the purpose of this article we will focus on IPV4 rules. Next we will want to copy the rules below into our rules.v4 file. Of course the rules will need to be modified to fit your environment.

# Generated by iptables-save v1.3.3 on Wed Apr 9 10:51:08 2008
# Flush out any rules that are already in there
*filter
:INPUT ACCEPT [146:11332]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [104:9831]
 
# Allow internal loopback connections
-A INPUT -i lo -j ACCEPT
-A OUTPUT -o lo -j ACCEPT
 
# Allow pinging
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
 
# Allow any outbound data, and any inbound data related to a connection that is already in use
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT
 
# =========BEGIN SERVER SPECIFIC PORT OPEN RULES=========
# Allow SCP/SSH Access from Green & Blue Subnet
-A INPUT -s 172.16.12.0/255.255.255.0 -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -s 10.10.12.0/255.255.255.0 -p tcp -m tcp --dport 22 -j ACCEPT
 
# Allow HTTP Access from Red Subnet/Internet
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 80 -j ACCEPT
 
# Allow HTTPS Access from Red Subnet/Internet
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 443 -j ACCEPT
 
# Allow MySQL Access from Red Subnet/Internet
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 3306 -j ACCEPT
 
# Allow FTP Access from Red Subnet/Internet
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 21 -j ACCEPT
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 58000:58010 -j ACCEPT
# =========END SERVER SPECIFIC PORT OPEN RULES=========
 
# Drop everything that hasn't been picked up by one of the rules above
-A INPUT -j DROP
-A FORWARD -j DROP
-A OUTPUT -j DROP
 
COMMIT
# Completed on Wed Apr 9 10:51:08 2008

Lastly, in order for our new rules to take affect, we simply need to start the netfilter-persistent service as seen below. That’s it, you now have a fully functional IPTables based firewall.

# Start netfilter-persistent Service
service netfilter-persistent start

# Check if IPTables were applied
iptables -L

Securing your server with iptables

In the Getting Started guide, you learned how to deploy a Linux distribution, boot your Linode and perform some basic administrative tasks. Now it’s time to harden your Linode to protect it from unauthorized access.

Update Your System–Frequently

Keeping your software up to date is the single biggest security precaution you can take for any operating system–be it desktop, mobile or server. Software updates frequently contain patches ranging from critical vulnerabilities to minor bug fixes, and many software vulnerabilities are actually patched by the time they become public.

Automatic Security Updates

There are opposing arguments for and against automatic updates on servers. Nonetheless, CentOS, Debian, Fedora and Ubuntu can be automatically updated to various extents. Fedora’s Wiki has a good breakdown of the pros and cons, but if you limit updates to those for security issues, the risk of using automatic updates will be minimal.

The practicality of automatic updates must be something which you judge for yourself because it comes down to what you do with your Linode. Bear in mind that automatic updates apply only to packages sourced from repositories, not self-compiled applications. You may find it worthwhile to have a test environment which replicates your production server. Updates can be applied there and reviewed for issues before being applied to the live environment.

• CentOS uses yum-cron for automatic updates.
• Debian and Ubuntu use unattended upgrades.
• Fedora uses dnf-automatic.

Add a Limited User Account

Up to this point, you have accessing your Linode as the root user. The concern here is that roothas unlimited privileges and can execute any command–even one that could accidentally break your server. For this reason and others, we recommend creating a limited user account and using that at all times. Administrative tasks will be done using sudo to temporarily elevate your limited user’s privileges so you can administer your server without logging in as root.

To add a new user, log in to your Linode via SSH.

CentOS / Fedora

1. Create the user, replacing example_user with your desired username, and assign a password:

   useradd example_user && passwd example_user

2. Add the user to the wheel group for sudo privileges:

   usermod -aG wheel example_user

Debian / Ubuntu

1. Create the user, replacing example_user with your desired username. You’ll then be asked to assign the user a password.

   adduser example_user

2. Add the user to the sudo group so you’ll have administrative privileges:

   adduser example_user sudo

With your new user assigned, disconnect from your Linode as root:

exit

Log back in to your Linode as your new user. Replace example_user with your username, and the example IP address with your Linode’s IP address:

ssh [email protected]

Now you can administer your Linode from your new user account instead of root. Superuser commands can now be prefaced with sudo; for example, sudo iptables -L. Nearly all superuser commands can be executed with sudo, and those commands will be logged to /var/log/auth.log.

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Source: linuxhomenetworking.com

Introduction

Network security is a primary consideration in any decision to host a website as the threats are becoming more widespread and persistent every day. One means of providing additional protection is to invest in a firewall. Though prices are always falling, in some cases you may be able to create a comparable unit using the Linux iptables package on an existing server for little or no additional expenditure.
This chapter shows how to convert a Linux server into:

• A firewall while simultaneously being your home website’s mail, web and DNS server.
• A router that will use NAT and port forwarding to both protect your home network and have another web server on your home network while sharing the public IP address of your firewall.

Creating an iptables firewall script requires many steps, but with the aid of the sample tutorials, you should be able to complete a configuration relatively quickly.

What Is iptables?

Originally, the most popular firewall/NAT package running on Linux was ipchains, but it had a number of shortcomings. To rectify this, the Netfilter organization decided to create a new product called iptables, giving it such improvements as:

• Better integration with the Linux kernel with the capability of loading iptables-specific kernel modules designed for improved speed and reliability.
• Stateful packet inspection. This means that the firewall keeps track of each connection passing through it and in certain cases will view the contents of data flows in an attempt to anticipate the next action of certain protocols. This is an important feature in the support of active FTP and DNS, as well as many other network services.
• Filtering packets based on a MAC address and the values of the flags in the TCP header. This is helpful in preventing attacks using malformed packets and in restricting access from locally attached servers to other networks in spite of their IP addresses.
• System logging that provides the option of adjusting the level of detail of the reporting.
• Better network address translation.
• Support for transparent integration with such Web proxy programs as Squid.
• A rate limiting feature that helps iptables block some types of denial of service (DoS) attacks.

Considered a faster and more secure alternative to ipchains, iptables has become the default firewall package installed under RedHat and Fedora Linux.

Download And Install The Iptables Package

Before you begin, you need to make sure that the iptables software RPM is installed. (See Chapter 6, « Installing Linux Software« , if you need a refresher.) When searching for the RPMs, remember that the filename usually starts with the software package name by a version number, as in iptables-1.2.9-1.0.i386.rpm.

Managing the iptables Server

Managing the iptables daemon is easy to do, but the procedure differs between Linux distributions. Here are some things to keep in mind.

• Firstly, different Linux distributions use different daemon management systems. Each system has its own set of commands to do similar operations. The most commonly used daemon management systems are SysV and Systemd.
• Secondly, the daemon name needs to be known. In this case the name of the daemon is iptables.

Armed with this information you can know how to:

• Start your daemons automatically on booting
• Stop, start and restart them later on during troubleshooting or when a configuration file change needs to be applied.

For more details on this, please take a look at the « Managing Daemons » section of Chapter 6 « Installing Linux Software »

Note: Remember to configure your daemon to start automatically upon your next reboot.

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