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How To Protect an Apache Server with Fail2Ban on Ubuntu 14.04

PostedAugust 14, 2015 128k views Security Apache Firewall

Introduction

When operating a web server, it is important to implement security measures to protect your site and users. Protecting your web sites and applications with firewall policies and restricting access to certain areas with password authentication is a great starting point to securing your system. However, any publicly accessible password prompt is likely to attract brute force attempts from malicious users and bots.

Setting up fail2ban can help alleviate this problem. When users repeatedly fail to authenticate to a service (or engage in other suspicious activity), fail2ban can issue a temporary bans on the offending IP address by dynamically modifying the running firewall policy. Each fail2ban "jail" operates by checking the logs written by a service for patterns which indicate failed attempts. Setting up fail2ban to monitor Apache logs is easy using the included configuration filters.

In this guide, we will demonstrate how to install fail2ban and configure it to monitor your Apache logs for intrusion attempts. We will use an Ubuntu 14.04 server.

Prerequisites

Before you begin, you should have an Ubuntu 14.04 server set up with a non-root account. This account should be configured with sudo privileges in order to issue administrative commands. To learn how to set up a user with sudo privileges, follow our initial server setup guide for Ubuntu 14.04.

Installing Apache and Configuring Password Authentication

If you are interested in protecting your Apache server with fail2ban, you might already have a server set up and running. If not, you can install Apache from Ubuntu's default repositories using apt.

Update the local package index and install by typing:

  • sudo apt-get update
  • sudo apt-get install apache2

The fail2ban service is useful for protecting login entry points. In order for this to be useful for an Apache installation, password authentication must be implemented for at least a subset of the content on the server. You can follow this guide to configure password protection for your Apache server.

Install Fail2Ban

Once your Apache server is running and password authentication is enabled, you can go ahead and install fail2ban (we include another repository re-fetch here in case you already had Apache set up in the previous steps):

  • sudo apt-get update
  • sudo apt-get install fail2ban

This will install the software. By default, fail2ban is configured to only ban failed SSH login attempts. We need to enable some rules that will configure it to check our Apache logs for patterns that indicate malicious activity.

Adjusting the General Settings within Fail2Ban

To get started, we need to adjust the configuration file that fail2ban uses to determine what application logs to monitor and what actions to take when offending entries are found. The supplied /etc/fail2ban/jail.conf file is the main provided resource for this.

To make modifications, we need to copy this file to /etc/fail2ban/jail.local. This will prevent our changes from being overwritten if a package update provides a new default file:

  • sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local

Open the newly copied file so that we can set up our Apache log monitoring:

  • sudo nano /etc/fail2ban/jail.local

Changing Defaults

We should start by evaluating the defaults set within the file to see if they suit our needs. These will be found under the [DEFAULT] section within the file. These items set the general policy and can each be overridden in specific jails.

One of the first items to look at is the list of clients that are not subject to the fail2ban policies. This is set by the ignoreip directive. It is sometimes a good idea to add your own IP address or network to the list of exceptions to avoid locking yourself out. This is less of an issue with web server logins though if you are able to maintain shell access, since you can always manually reverse the ban. You can add additional IP addresses or networks delimited by a space, to the existing list:

/etc/fail2ban/jail.local
[DEFAULT]

. . .
ignoreip = 127.0.0.1/8 your_home_IP

Another item that you may want to adjust is the bantime, which controls how many seconds an offending member is banned for. It is ideal to set this to a long enough time to be disruptive to a malicious actor's efforts, while short enough to allow legitimate users to rectify mistakes. By default, this is set to 600 seconds (10 minutes). Increase or decrease this value as you see fit:

/etc/fail2ban/jail.local
[DEFAULT]

. . .
bantime = 3600

The next two items determine the scope of log lines used to determine an offending client. The findtime specifies an amount of time in seconds and the maxretry directive indicates the number of attempts to be tolerated within that time. If a client makes more than maxretry attempts within the amount of time set by findtime, they will be banned:

/etc/fail2ban/jail.local
[DEFAULT]

. . .
findtime = 3600   # These lines combine to ban clients that fail
maxretry = 6      # to authenticate 6 times within a half hour.

Setting Up Mail Notifications (Optional)

You can enable email notifications if you wish to receive mail whenever a ban takes place. To do so, you will have to first set up an MTA on your server so that it can send out email. To learn how to use Postfix for this task, follow this guide.

Once you have your MTA set up, you will have to adjust some additional settings within the [DEFAULT] section of the /etc/fail2ban/jail.local file. Start by setting the mta directive. If you set up Postfix, like the above tutorial demonstrates, change this value to "mail":

/etc/fail2ban/jail.local
[DEFAULT]

. . .
mta = mail

You need to select the email address that will be sent notifications. Modify the destemail directive with this value. The sendername directive can be used to modify the "Sender" field in the notification emails:

/etc/fail2ban/jail.local
[DEFAULT]

. . .
destemail = youraccount@email.com
sendername = Fail2BanAlerts

In fail2ban parlance, an "action" is the procedure followed when a client fails authentication too many times. The default action (called action_) is to simply ban the IP address from the port in question. However, there are two other pre-made actions that can be used if you have mail set up.

You can use the action_mw action to ban the client and send an email notification to your configured account with a "whois" report on the offending address. You could also use the action_mwl action, which does the same thing, but also includes the offending log lines that triggered the ban:

/etc/fail2ban/jail.local
[DEFAULT]

. . .
action = %(action_mwl)s

Configuring Fail2Ban to Monitor Apache Logs

Now that you have some of the general fail2ban settings in place, we can concentrate on enabling the Apache-specific jails that will monitor our web server logs for specific behavior patterns.

Each jail within the configuration file is marked by a header containing the jail name in square brackets (every section but the [DEFAULT] section indicates a specific jail's configuration). By default, only the [ssh] jail is enabled.

To enable log monitoring for Apache login attempts, we will enable the [apache] jail. Edit the enabled directive within this section so that it reads "true":

/etc/fail2ban/jail.local
[apache]

enabled  = true
port     = http,https
filter   = apache-auth
logpath  = /var/log/apache*/*error.log
maxretry = 6
. . .

If your Apache server is writing to the default log location (/var/log/apache/error.log) the jail is already configured to look in the correct place. If you are logging to a different location, modify the logpath as needed. Also, feel free to adjust the maxretry directive or add a findtime value for this jail if you wish to set different restrictions for this specific jail:

/etc/fail2ban/jail.local
[apache]

enabled  = true
port     = http,https
filter   = apache-auth
logpath  = /var/log/apache/custom_log_location.log
maxretry = 3
findtime = 600
. . .

The above jail will take care of banning basic authentication failures. There are also some other pre-configured jails that are worth enabling (the [apache-multiport] jail is a legacy jail that is not needed).

The [apache-noscript] jail is used to ban clients that are searching for scripts on the website to execute and exploit. If you do not use PHP or any other language in conjunction with your web server, you can enable this jail to ban those who request these types of resources:

/etc/fail2ban/jail.local
[apache-noscript]

enabled  = true
. . .

The [apache-overflows] jail is used to block clients who are attempting to request unusually long and suspicious URLs. These are often signs of attempts to exploit Apache by trying to trigger a buffer overflow. You can enable this jail if you wish to prevent these types of attacks:

/etc/fail2ban/jail.local
[apache-overflows]

enabled  = true
. . .

Some additional checks can be made by copying and pasting the [apache-overflows] entry and modifying it slightly. For instance, you can copy and paste that section and modify the jail name and filter to apache-badbots to stop some known malicious bot request patterns:

/etc/fail2ban/jail.local
[apache-overflows]

enabled  = true
port     = http,https
filter   = apache-overflows
logpath  = /var/log/apache*/*error.log
maxretry = 2

[apache-badbots]

enabled  = true
port     = http,https
filter   = apache-badbots
logpath  = /var/log/apache*/*error.log
maxretry = 2

If you do not use Apache to provide access to web content within users' home directories, you can copy and paste again and change the jail and filter names to apache-nohome:

/etc/fail2ban/jail.local
[apache-overflows]

enabled  = true
port     = http,https
filter   = apache-overflows
logpath  = /var/log/apache*/*error.log
maxretry = 2

[apache-badbots]

enabled  = true
port     = http,https
filter   = apache-badbots
logpath  = /var/log/apache*/*error.log
maxretry = 2

[apache-nohome]

enabled  = true
port     = http,https
filter   = apache-nohome
logpath  = /var/log/apache*/*error.log
maxretry = 2

Lastly, if you are using Apache with PHP, you may want to enable the [php-url-fopen] jail, which blocks attempts to use certain PHP behavior for malicious purposes. You will likely have to change the logpath directive to point the correct access log location (on Ubuntu, the default location is /var/log/apache2/access.log). You can use a pattern similar to the one that matches the error log in the other jails:

/etc/fail2ban/jail.local
[php-url-fopen]

enabled = true
port    = http,https
filter  = php-url-fopen
logpath = /var/log/apache*/*access.log

When you are finished making the modifications you need, save and close the file.

Implementing your Apache Jails

To implement your configuration changes, you'll need to restart the fail2ban service. You can do that by typing:

  • sudo service fail2ban restart

The service should restart, implementing the different banning policies you've configured.

Getting Info About Enabled Jails

You can see all of your enabled jails by using the fail2ban-client command:

  • sudo fail2ban-client status

You should see a list of all of the jails you enabled:

Output
Status |- Number of jail: 7 `- Jail list: php-url-fopen, apache-overflows, apache-noscript, ssh, apache-badbots, apache-nohome, apache

You can see that fail2ban has modified your firewall rules to create a framework for banning clients. Even with no previous firewall rules, you would now have a framework enabled that allows fail2ban to selectively ban clients by adding them to purpose-built chains:

  • sudo iptables -S
Output
-P INPUT ACCEPT -P FORWARD ACCEPT -P OUTPUT ACCEPT -N fail2ban-apache -N fail2ban-apache-badbots -N fail2ban-apache-nohome -N fail2ban-apache-noscript -N fail2ban-apache-overflows -N fail2ban-php-url-fopen -N fail2ban-ssh -A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache-nohome -A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache-badbots -A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-php-url-fopen -A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache-overflows -A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache-noscript -A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache -A INPUT -p tcp -m multiport --dports 22 -j fail2ban-ssh -A fail2ban-apache -j RETURN -A fail2ban-apache-badbots -j RETURN -A fail2ban-apache-nohome -j RETURN -A fail2ban-apache-noscript -j RETURN -A fail2ban-apache-overflows -j RETURN -A fail2ban-php-url-fopen -j RETURN -A fail2ban-ssh -j RETURN

If you want to see the details of the bans being enforced by any one jail, it is probably easier to use the fail2ban-client again:

  • sudo fail2ban-client status apache
Output
Status for the jail: apache |- filter | |- File list: /var/log/apache2/error.log | |- Currently failed: 0 | `- Total failed: 0 `- action |- Currently banned: 0 | `- IP list: `- Total banned: 0

Testing Fail2Ban Policies

It is important to test your fail2ban policies to ensure they block traffic as expected. For instance, for the Apache authentication prompt, you can give incorrect credentials a number of times. After you have surpassed the limit, you should be banned and unable to access the site. If you set up email notifications, you should see messages regarding the ban in the email account you provided.

If you look at the status with the fail2ban-client command, you will see your IP address being banned from the site:

  • sudo fail2ban-client status apache
Output
Status for the jail: apache |- filter | |- File list: /var/log/apache2/error.log | |- Currently failed: 0 | `- Total failed: 12 `- action |- Currently banned: 1 | `- IP list: 111.111.111.111 `- Total banned: 1

When you are satisfied that your rules are working, you can manually un-ban your IP address with the fail2ban-client by typing:

  • sudo fail2ban-client set apache unbanip 111.111.111.111

You should now be able to attempt authentication again.

Conclusion

Setting up fail2ban to protect your Apache server is fairly straight forward in the simplest case. However, fail2ban provides a great deal of flexibility to construct policies that will suit your specific security needs. By taking a look at the variables and patterns within the /etc/fail2ban/jail.local file, and the files it depends on within the /etc/fail2ban/filter.d and /etc/fail2ban/action.d directories, you can find many pieces to tweak and change as your needs evolve. Learning the basics of how to protect your server with fail2ban can provide you with a great deal of security with minimal effort.

To learn more about fail2ban, take a look at some of these links:

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