June 14, 2012

Beginner

How To Protect SSH with fail2ban on CentOS 6

About Fail2Ban


Servers do not exist in isolation, and those servers with only the most basic SSH configuration can be vulnerable to brute force attacks. fail2ban provides a way to automatically protect the server from malicious signs. The program works by scanning through log files and reacting to offending actions such as repeated failed login attempts.

Step One—Install Fail2Ban


Because fail2ban is not available from CentOS, we should start by downloading the EPEL repository:
rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

Follow up by installing fail2ban:
yum install fail2ban

Step Two—Copy the Configuration File


The default fail2ban configuration file is location at /etc/fail2ban/jail.conf. The configuration work should not be done in that file, however, and we should instead make a local copy of it.
cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local

After the file is copied, you can make all of your changes within the new jail.local file. Many of possible services that may need protection are in the file already. Each is located in its own section, configured and turned off.

Step Three—Configure defaults in Jail.Local


Open up the the new fail2ban configuration file:
vi /etc/fail2ban/jail.local

The first section of defaults covers the basic rules that fail2ban will follow. If you want to set up more nuanced protection for your virtual private server, you can customize the details in each section.

You can see the default section below.
[DEFAULT]

# "ignoreip" can be an IP address, a CIDR mask or a DNS host. Fail2ban will not
# ban a host which matches an address in this list. Several addresses can be
# defined using space separator.
ignoreip = 127.0.0.1

# "bantime" is the number of seconds that a host is banned.
bantime  = 3600

# A host is banned if it has generated "maxretry" during the last "findtime"
# seconds.
findtime  = 600

# "maxretry" is the number of failures before a host get banned.
maxretry = 3

Write your personal IP address into the ignoreip line. You can separate each address with a space. IgnoreIP allows you white list certain IP addresses and make sure that they are not locked out from your VPS. Including your address will guarantee that you do not accidentally ban yourself from your own virtual private server.

The next step is to decide on a bantime, the number of seconds that a host would be blocked from the server if they are found to be in violation of any of the rules. This is especially useful in the case of bots, that once banned, will simply move on to the next target. The default is set for 10 minutes—you may raise this to an hour (or higher) if you like.

Maxretry is the amount of incorrect login attempts that a host may have before they get banned for the length of the ban time.

Findtime refers to the amount of time that a host has to log in. The default setting is 10 minutes; this means that if a host attempts, and fails, to log in more than the maxretry number of times in the designated 10 minutes, they will be banned.

Step Four (Optional)—Configure the ssh-iptables Section in Jail.Local


The SSH details section is just a little further down in the config, and it is already set up and turned on. Although you should not be required to make to make any changes within this section, you can find the details about each line below.
[ssh-iptables]

enabled  = true
filter   = sshd
action   = iptables[name=SSH, port=ssh, protocol=tcp]
           sendmail-whois[name=SSH, dest=root, sender=[email protected]]
logpath  = /var/log/secure
maxretry = 5

Enabled simply refers to the fact that SSH protection is on. You can turn it off with the word "false".

The filter, set by default to sshd, refers to the config file containing the rules that fail2banuses to find matches. The name is a shortened version of the file extension. For example, sshd refers to the /etc/fail2ban/filter.d/sshd.conf.

Action describes the steps that fail2ban will take to ban a matching IP address. Just like the filter entry, each action refers to a file within the action.d directory. The default ban action, "iptables" can be found at /etc/fail2ban/action.d/iptables.conf .

In the "iptables" details, you can customize fail2ban further. For example, if you are using a non-standard port, you can change the port number within the brackets to match, making the line look more like this:
 eg. iptables[name=SSH, port=30000, protocol=tcp]

You can change the protocol from TCP to UDP in this line as well, depending on which one you want fail2ban to monitor.

If you have a mail server set up on your virtual private server, Fail2Ban can email you when it bans an IP address. In the default case, the sendmail-whois refers to the actions located at /etc/fail2ban/action.d/sendmail-whois.conf.

log path refers to the log location that fail2ban will track.

The max retry line within the SSH section has the same definition as the default option. However, if you have enabled multiple services and want to have specific values for each one, you can set the new max retry amount for SSH here.

Step Five—Restart Fail2Ban


After making any changes to the fail2ban config, always be sure to restart Fail2Ban:
sudo service fail2ban restart

You can see the rules that fail2ban puts in effect within the IP table:
iptables -L




By Etel Sverdlov

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21 Comments

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  • Gravatar hello about 1 year

    Hi Thanks The EPEL links failed. I find the new one: http://mirrors.ircam.fr/pub/fedora/epel/6/i386/repoview/epel-release.html

  • Gravatar xandr2 about 1 year

    Hi, good article! If you add third-party repo i recommend using a yum-plugin-priorities! This plugin is particularly useful for anyone who uses one or more third-party repositories, as these repositories may update system files, which can potentially compromise the stability of your CentOS installation. http://wiki.centos.org/PackageManagement/Yum/Priorities

  • Gravatar Manos Kantzanos about 1 year

    In my opinion is a much better way (easy & safe). Specifically: STEP 1: Install EPEL repo (eg. for CentOS x64) wget http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm yum install epel-release-6-8.noarch.rpm STEP 2: Disable EPEL repo by default vi /etc/yum.repos.d/epel.repo change enabled=1 --> enabled=0 STEP 3: Anytime you want to include EPEL repo from command line: yum --enblerepo=epel I hope it helps. Manos

  • Gravatar digitalocean about 1 year

    Please update the link on this post as it is broken.

  • Gravatar David Levy about 1 year

    I used the enitre repo for my OS version and arch type with this article: http://www.tecmint.com/how-to-enable-epel-repository-for-rhel-centos-6-5/ using: ## RHEL/CentOS 6 64-Bit ## # sudo wget http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm # sudo rpm -ivh epel-release-6-8.noarch.rpm # sudo yum repolist # sudo yum --enablerepo=epel info fail2ban # sudo yum --enablerepo=epel install fail2ban root user login is ofc disabled. Anyway this method worked for me.

  • Gravatar David Levy about 1 year

    Also is the a tutorial on how to use fail2ban with vsftp?

  • Gravatar lhnmuniz 12 months

    sudo rpm -Uvh http://mirror.globo.com/epel/6/i386/epel-release-6-8.noarch.rpm

  • Gravatar Arunava 10 months

    @Manos Please explain why you are disabling it and what are the security repercussions if not done

  • Gravatar asymmetric.world 9 months

    epel-release-6-8.noarch.rpm is latest release. for 32-bit system, use rpm -Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm for 64-bit system, use rpm -Uvh http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

  • Gravatar victor0110 7 months

    I am afraid that fail2ban is not interacting with my iptables: $ yum install -y fail2ban $ cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local $ service fail2ban restart $ iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination

  • Gravatar Kamal Nasser 7 months

    @victor0110: I believe fail2ban doesn't modify/add iptables rules right away, it'll have to process logs first and if anything matches, it'll create rules and add them to iptables.

  • Gravatar imran 6 months

    I have find an another like for epel repository for centos 64_x rpm -Uvh http://mirror.nus.edu.sg/fedora/epel/6/x86_64/epel-release-6-8.noarch.rpm Regards: imran http://aicheapwebhosting.com

  • Gravatar Paul Ridney 6 months

    One thing missing is to make sure fail2ban starts on server boot, using the following command: sudo chkconfig fail2ban on Matt

  • Gravatar sanjaysubramanian 5 months

    I got my server on 11/14/2013 rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm Retrieving http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm Preparing... ########################################### [100%] package epel-release-6-8.noarch is already installed So I just went ahead with yum install fail2ban

  • Gravatar qasim2490 5 months

    hi i have problem in fail2ban i have installed and configure fail2ban configured successfully. iptables -L returns Chain INPUT (policy ACCEPT) target prot opt source destination fail2ban-SSH tcp -- anywhere anywhere tcp dpt:ssh Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination Chain fail2ban-SSH (1 references) target prot opt source destination RETURN all -- anywhere anywhere but it is not blocking my ssh remote access.. :( please help me in this. regards Rao_Qasim

  • Gravatar Kamal Nasser 5 months

    @qasim2490: Did you try logging in to your droplet (with invalid credentials)?

  • Gravatar carlm 4 months

    Is it possible to allow a port like 80,443 etc? So lets say the user is blocked on port 22 (SSH) because of too many failed login attempts could i still allow them to connect on 80 and 443 but block all other ports? Thanks.

  • Gravatar carlm 4 months

    Correction and more details: Is it possible to allow some ports like 80,443, etc but block all the others? So lets say the user is blocked because of too many failed login attempts on SSH could i still allow them to connect on 80 and 443 but block all other ports? This is in case a genuine user gets blocked and they could still connect to the server via HTTP/HTTPS. Thanks.

  • Gravatar yazirarafath about 1 month

    Thank you. Working without any hassle!

  • Gravatar Igor 10 days

    In several articles I saw : ulimit -s 256 - to limit memory usage... Where should I add it to?

  • Gravatar Kamal Nasser 9 days

    @Igor: ulimit is a bash built-in, which means it will only be applied to process that are started from the bash session that you ran the ulimit command in. I'm not sure where you need to limit memory usage.

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