HOWTO fail2ban 0.7.x

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HowTo test the new development branch

For quite a long time now, a new branch is in development. This is almost a complete rewrite with a lot of new features and a better design. There is still a lot of work but this new branch is already functional and can be tested.

This HowTo will not delete or modify your current Fail2ban setup. You only have to turn off any previous version during the tests.

Getting the sources

There is two ways of getting the sources:

There is no official release of the 0.7 branch (trunk) yet. The best way for getting the sources is Subversion. The instructions are available here but here is a quick reminder:

svn co https://svn.sourceforge.net/svnroot/fail2ban/trunk fail2ban-trunk

The sources are now available in the directory called fail2ban-trunk. If you decide to use the tarball, simply run:

tar xvfj fail2ban-nightly.tar.bz2

You should have a directory called fail2ban-0.7.5-SVN.

Change your current directory to fail2ban-trunk or fail2ban-0.7.5-SVN.

Setup

The configuration folder should look like this:

config/
|-- action.d
|   |-- dummy.conf
|   |-- foo.conf
|   |-- hostsdeny.conf
|   |-- iptables.conf
|   |-- mail-whois.conf
|   `-- mail.conf
|-- fail2ban.conf
|-- filter.d
|   |-- apache-auth.conf
|   |-- sshd.conf
|   `-- vsftpd.conf
`-- jail.conf

The most important file is probably jail.conf. It contains the definition of your jails. A jail is the combination of one filter and one or several actions. More information about the jail concept are available here. You can override configuration files using a .local file. Per example, config/fail2ban.local overrides the settings in config/fail2ban.conf.

For this tutorial, we will setup a configuration similar to what previous versions do: parse SSH logs, ban hosts using iptables and send notification e-mails.

SSH filter setup

The default configuration for the SSH filter should not require too much changes. You can adapt the regular expression to meet your needs. I suggest you try fail2ban-regex. This is a small tool which allow you to test your regular expression.

./fail2ban-regex "1157520814 rblsmtpd: 212.53.135.257 pid 19597 sbl-xbl.test.org: 451
http://www.test.org/query/bl? ip=212.53.135.257" "(?:[\d,.] [\d,.] rblsmtpd: |421
badiprbl: ip)(?P<host>\S*)"

Success, the following data were found:
Date: Wed Sep 06 06:33:34 2006
IP  : 212.53.135.257

Date template hits:
0 hit: Month Day Hour:Minute:Second
0 hit: Weekday Month Day Hour:Minute:Second Year
0 hit: TAI64N
1 hit: Epoch

Benchmark. Executing 1000...
Performance
Avg: 0.089841365814208984 ms
Max: 4.3938159942626953 ms (Run 175)
Min: 0.073909759521484375 ms (Run 914)

Iptables action setup

The Iptables script should be fine. However, some settings have to be set in config/jail.conf.

Jail setup

We are now able to define our first jail. We do not have to change anything in config/filter.d/sshd.conf or config/action.d/iptables.conf. This is quite useful when upgrading or if you want to save your own changes. Adapt the value of logpath to point to your SSH daemon log file and set bantime to 600 which is 10 minutes.

[ssh]

enabled  = true
filter   = sshd
action   = iptables[name=ssh,port=22,protocol=tcp]
           mail[name=SSH,dest=toto@titi.com]
logpath  = /var/log/pwdfail/current
bantime  = 600
maxretry = 3

Since 0.7.3, Fail2ban can watch several files in one jail and logpath supports wildcards. For example, you can put:

logpath = /home/www/*/error_log

The filter option is the name of a file in config/filter.d without the .conf extension. The action field is more interesting. Here, we set as first action the iptables script. Action script can have parameters. Have a look at config/action.d/iptables.conf. Please, be aware that no spaces are allowed in the parameters field. This will be fixed in the future. We define a second action. It will send a notification e-mail. Just replace the dest parameter with your e-mail address. Be aware that the mail script uses the mail command of the system. Ensure this command works on your box.

There is already a few jails template in jail.conf. They should help you starting writing your own jails.

Client/Server

Fail2ban is now composed of two parts: a server and a client. The server listens on a socket and waits for commands. It monitors log files and executes actions. The client part is used to communicate with the server. It converts the config/ settings into commands which are sent to the server through a Unix socket.

For this tutorial, you will need root access. This is not necessary for testing but you will need it to access iptables on most systems.

We will first test whether the configuration directory can be parse correctly. If you do not have a /etc/fail2ban directory with the configuration files, use the -c option to give your configuration folder. Runs the following command:

# ./fail2ban-client -c ./config -d

or

# fail2ban-client -d

Check that no exceptions are triggered. Here you should get a lot of output like:

['set', 'loglevel', 3]
['set', 'logtarget', 'STDERR']
['add', 'ssh']
['set', 'ssh', 'bantime', 600]
['set', 'ssh', 'logpath', '/var/log/pwdfail/current']
['set', 'ssh', 'maxretry', 3]

These are the commands which will be sent to the server. You could send them manually with:

# ./fail2ban-client set loglevel 3

But it would be a bit annoying. The whole configuration is automatically sent to the server on startup. So, it is time to start it:

# ./fail2ban-client start

The server should now start monitoring the log file. Look at the server terminal. If you do not see anything, output are maybe redirected into the log file /var/log/fail2ban.log. You can change this in config/fail2ban.conf or, better, create your own config/fail2ban.local. You can also change this in realtime with:

# ./fail2ban-client set logtarget STDERR

All of this without restarting the server which is carefully watching your log files during the operation. Mmmmhhh... Three retries are a bit too agressive? Change the setting with:

# ./fail2ban-client set ssh maxretry 5

You do not need to restart anything. The changes are taken into account directly. Maybe you saw the RRDTool plot at the end of the Screenshots page. The information for this graph come from the following command:

# ./fail2ban-client status ssh
Status for the jail: ssh
|- filter
|  |- Currently failed:         0
|  `- Total failed:             37
`- action
   |- Currently banned:         1
   `- Total banned:             12

You can stop the server with the following command:

# ./fail2ban-client stop

You can also type all the previous commands in the interactive mode. Simply run:

# ./fail2ban-client -i

You know have a prompt where you can directly type the previous commands without having to call fail2ban-client everytime.

# ./fail2ban-client -i
Fail2Ban v0.7.2 reads log file that contains password failure report
and bans the corresponding IP addresses using firewall rules.

fail2ban> status
Status
|- Number of jail:      1
`- Jail list:           ssh-iptables
fail2ban>

If you want to help with Python programming, documentation, etc, do not hesitate to contact me.

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