Difference between revisions of "Fail2ban"

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Fail2ban scans log files like /var/log/pwdfail or /var/log/apache/error_log and bans IP that makes too many password failures. It updates firewall rules to reject the IP address.  
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[[Category:Secure Shell]]
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[[ro:Fail2ban]]
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{{Warning|Using an IP blacklist will stop trivial attacks but it relies on an additional daemon and successful logging (the partition containing /var can become full, especially if an attacker is pounding on the server). Additionally, if the attacker knows your IP address, they can send packets with a spoofed source header and get you locked out of the server. [[SSH keys]] provide an elegant solution to the problem of brute forcing without these problems.}}
  
=Installation=
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[http://www.fail2ban.org/wiki/index.php/Main_Page Fail2ban] scans log files like {{ic|/var/log/pwdfail}} or {{ic|/var/log/apache/error_log}} and bans IP that makes too many password failures. It updates firewall rules to reject the IP address.
First, we need to install Gamin so that fail2ban can detect modification to the log files. See this [[Gamin|page]]. Generally, you will just have to do :
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#pacman -S gamin
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Then you can install fail2ban
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==Installation==
  #pacman -S fail2ban
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First, install python2-pyinotify so that Fail2ban can detect modification to the log files:
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  # pacman -S python2-pyinotify
  
If you want fail2ban to send an email when someone has been banned, you have to configure [[SSMTP]] (for example). You will also have to install whois to get some information about the ''attacker''.
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Then, install {{Pkg|fail2ban}}:
  #pacman -S whois
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  # pacman -S fail2ban
  
=SSH jail=
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If you want Fail2ban to send an email when someone has been banned, you have to configure [[SSMTP]] (for example). You will also have to install {{Pkg|whois}} to get some information about the ''attacker''.
Edit {{Filename|/etc/fail2ban/jail.conf}} and modify ssh-iptables section to enable it and configure the action.
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# pacman -S whois
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===systemd===
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Use the service unit fail2ban.service, consult [[systemd]] for instructions
  
If your firewall is iptables :
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Please note that this currently requires {{ic|syslog-ng}} logging. This is because a pure systemd {{ic|journalctl}} does not log to {{ic|/var/log/auth.log}} which is parsed by the service in default.
<pre>
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[ssh-iptables]
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enabled  = true
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filter  = sshd
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action  = iptables[name=SSH, port=ssh, protocol=tcp]                                       
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          sendmail-whois[name=SSH, dest=your@mail.org, sender=fail2ban@mail.com]
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logpath  = /var/log/auth.log                                                                  
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maxretry = 5
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</pre>
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If your firewall is shorewall :
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==Hardening==
<pre>
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Currently, fail2ban requires to run as root, therefore you may wish to consider some additional hardening on the process with systemd. Ref:[http://0pointer.de/blog/projects/security.html systemd for Administrators, Part XII]
[ssh-iptables]
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===Capabilities===
enabled  = true
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For added security consider limiting fail2ban capabilities by adding ''CapabilityBoundingSet'' under {{ic|[Service]}} section of the systemd service file, e.g.:
filter  = sshd
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CapabilityBoundingSet=CAP_DAC_READ_SEARCH CAP_NET_ADMIN CAP_NET_RAW
action  = shorewall
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In the example above, '''CAP_DAC_READ_SEARCH''' will allow fail2ban full read access, and '''CAP_NET_ADMIN''' and '''CAP_NET_RAW''' allow setting of firewall rules with [[iptables]]. Additional capabilities may be required, depending on your fail2ban configuration. See {{ic|man capabilities}} for more info.
          sendmail-whois[name=SSH, dest=your@mail.org, sender=fail2ban@mail.com]
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===Filesystem Access===
logpath  = /var/log/auth.log                                                                     
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Also considering limiting file system read and write access, by using ''ReadOnlyDirectories'' and ''ReadWriteDirectories'', again under the under {{ic|[Service]}} section. For example:
maxretry = 5
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ReadOnlyDirectories=/
</pre>
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ReadWriteDirectories=/var/run/fail2ban /var/spool/postfix/maildrop
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In the example above, this limits the file system to read-only, except for {{ic|/var/run/fail2ban}} for pid and socket files, and {{ic|/var/spool/postfix/maildrop}} for [[postfix]] sendmail. Again, this will be dependent on you system configuration and fail2ban configuration. Note that adding {{ic|/var/log}} is necessary if you want fail2ban to log its activity.
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 +
==SSH jail==
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Edit {{ic|/etc/fail2ban/jail.conf}} and modify the ssh-iptables section to enable it and configure the action.
 +
 
 +
If your firewall is iptables:
 +
[ssh-iptables]
 +
enabled  = true
 +
filter  = sshd
 +
action  = iptables[name=SSH, port=ssh, protocol=tcp]                                       
 +
            sendmail-whois[name=SSH, dest=your@mail.org, sender=fail2ban@mail.com]
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logpath  = /var/log/auth.log                                                                   
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maxretry = 5
 +
 
 +
If your firewall is shorewall:
 +
[ssh-shorewall]
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enabled  = true
 +
filter  = sshd
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action  = shorewall
 +
            sendmail-whois[name=SSH, dest=your@mail.org, sender=fail2ban@mail.com]
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logpath  = /var/log/auth.log                                                                     
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maxretry = 5
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{{Note|You can set {{Ic|BLACKLISTNEWONLY}} to {{Ic|No}} in {{ic|/etc/shorewall/shorewall.conf}} otherwise the rule added to ban an IP address will affect only new connections.}}
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Also do not forget to add/change:
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LogLevel VERBOSE
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in your {{ic|/etc/ssh/sshd_config}}. Else, password failures are not logged correctly.
 +
 
 +
==See also==
 +
*[[sshguard]]

Revision as of 20:51, 23 January 2013

Warning: Using an IP blacklist will stop trivial attacks but it relies on an additional daemon and successful logging (the partition containing /var can become full, especially if an attacker is pounding on the server). Additionally, if the attacker knows your IP address, they can send packets with a spoofed source header and get you locked out of the server. SSH keys provide an elegant solution to the problem of brute forcing without these problems.

Fail2ban scans log files like /var/log/pwdfail or /var/log/apache/error_log and bans IP that makes too many password failures. It updates firewall rules to reject the IP address.

Installation

First, install python2-pyinotify so that Fail2ban can detect modification to the log files:

# pacman -S python2-pyinotify

Then, install fail2ban:

# pacman -S fail2ban

If you want Fail2ban to send an email when someone has been banned, you have to configure SSMTP (for example). You will also have to install whois to get some information about the attacker.

# pacman -S whois

systemd

Use the service unit fail2ban.service, consult systemd for instructions

Please note that this currently requires syslog-ng logging. This is because a pure systemd journalctl does not log to /var/log/auth.log which is parsed by the service in default.

Hardening

Currently, fail2ban requires to run as root, therefore you may wish to consider some additional hardening on the process with systemd. Ref:systemd for Administrators, Part XII

Capabilities

For added security consider limiting fail2ban capabilities by adding CapabilityBoundingSet under [Service] section of the systemd service file, e.g.:

CapabilityBoundingSet=CAP_DAC_READ_SEARCH CAP_NET_ADMIN CAP_NET_RAW

In the example above, CAP_DAC_READ_SEARCH will allow fail2ban full read access, and CAP_NET_ADMIN and CAP_NET_RAW allow setting of firewall rules with iptables. Additional capabilities may be required, depending on your fail2ban configuration. See man capabilities for more info.

Filesystem Access

Also considering limiting file system read and write access, by using ReadOnlyDirectories and ReadWriteDirectories, again under the under [Service] section. For example:

ReadOnlyDirectories=/
ReadWriteDirectories=/var/run/fail2ban /var/spool/postfix/maildrop

In the example above, this limits the file system to read-only, except for /var/run/fail2ban for pid and socket files, and /var/spool/postfix/maildrop for postfix sendmail. Again, this will be dependent on you system configuration and fail2ban configuration. Note that adding /var/log is necessary if you want fail2ban to log its activity.

SSH jail

Edit /etc/fail2ban/jail.conf and modify the ssh-iptables section to enable it and configure the action.

If your firewall is iptables:

[ssh-iptables]
enabled  = true
filter   = sshd
action   = iptables[name=SSH, port=ssh, protocol=tcp]                                         
           sendmail-whois[name=SSH, dest=your@mail.org, sender=fail2ban@mail.com]
logpath  = /var/log/auth.log                                                                    
maxretry = 5

If your firewall is shorewall:

[ssh-shorewall]
enabled  = true
filter   = sshd
action   = shorewall
           sendmail-whois[name=SSH, dest=your@mail.org, sender=fail2ban@mail.com]
logpath  = /var/log/auth.log                                                                    
maxretry = 5
Note: You can set BLACKLISTNEWONLY to No in /etc/shorewall/shorewall.conf otherwise the rule added to ban an IP address will affect only new connections.

Also do not forget to add/change:

LogLevel VERBOSE

in your /etc/ssh/sshd_config. Else, password failures are not logged correctly.

See also