Difference between revisions of "Fail2ban"

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[[Category:Secure Shell (English)]]
+
[[Category:Firewalls]]
{{i18n|Fail2ban}}
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[[Category:Secure Shell]]
[[ro:Fail2ban]]
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[[ja:Fail2ban]]
{{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.}}
+
[[ru:Fail2ban]]
 +
{{Related articles start}}
 +
{{Related|sshguard}}
 +
{{Related|Security}}
 +
{{Related articles end}}
 +
[http://www.fail2ban.org/wiki/index.php/Main_Page Fail2ban] scans log files (e.g. {{ic|/var/log/httpd/error_log}}) and bans IPs that show the malicious signs like too many password failures, seeking for exploits, etc. Generally Fail2Ban is then used to update firewall rules to reject the IP addresses for a specified amount of time, although any arbitrary other action (e.g. sending an email) could also be configured.  
  
[http://www.fail2ban.org/wiki/index.php/Main_Page Fail2ban] scans log files like {{Filename|/var/log/pwdfail}} or {{Filename|/var/log/apache/error_log}} and bans IP that makes too many password failures. It updates firewall rules to reject the IP address.
+
{{Warning|Using an IP banning software will stop trivial attacks but it relies on an additional daemon and successful logging. Additionally, if the attacker knows your IP address, they can send packets with a spoofed source header and get your IP address banned. Make sure to specify your IP in {{ic|ignoreip}}.}}
  
==Installation==
+
== Installation ==
First, install [[Gamin]] so that Fail2ban can detect modification to the log files:
 
# pacman -S gamin
 
  
Then, install {{Package Official|fail2ban}}:
+
[[Install]] {{Pkg|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 {{Package Official|whois}} to get some information about the ''attacker''.
+
== Usage ==
# pacman -S whois
 
  
Now you can start the {{Codeline|fail2ban}} daemon:
+
[[#Configuration|Configure]] fail2ban and [[enable]]/[[start]] {{ic|fail2ban.service}}.
# /etc/rc.d/fail2ban start
 
  
You can add it into DAEMONS array in {{Filename|/etc/rc.conf}}:
+
=== fail2ban-client ===
DAEMONS=(... fail2ban ...)
 
  
==SSH jail==
+
The fail2ban-client allows monitoring jails (reload, restart, status, etc.), to view all available commands:
Edit {{Filename|/etc/fail2ban/jail.conf}} and modify the ssh-iptables section to enable it and configure the action.
 
  
If your firewall is iptables:
+
$ fail2ban-client
  [ssh-iptables]
+
 
 +
To view all enabled jails:
 +
 
 +
# fail2ban-client status
 +
 
 +
To check the status of a jail, e.g. for ''sshd'':
 +
 
 +
{{hc|# fail2ban-client status sshd|<nowiki>
 +
Status for the jail: sshd
 +
|- Filter
 +
|  |- Currently failed: 1
 +
|  |- Total failed:    9
 +
|  `- Journal matches:  _SYSTEMD_UNIT=sshd.service + _COMM=sshd
 +
`- Actions
 +
  |- Currently banned: 1
 +
  |- Total banned:    1
 +
  `- Banned IP list:  0.0.0.0
 +
</nowiki>}}
 +
 
 +
== Configuration ==
 +
 
 +
Due to the possibility of the {{ic|/etc/fail2ban/jail.conf}} file being overwritten or improved during a distribution update, it is recommended to [[Create]] {{ic|/etc/fail2ban/jail.local}} file. For example to change default ban time to 1 day:
 +
 
 +
{{hc|/etc/fail2ban/jail.local|<nowiki>
 +
[DEFAULT]
 +
bantime = 1d
 +
</nowiki>}}
 +
 
 +
Or create separate ''name.local'' files under the {{ic|/etc/fail2ban/jail.d}} directory, e.g. {{ic|/etc/fail2ban/jail.d/sshd.local}}.
 +
 
 +
[[Restart]] {{ic|fail2ban.service}} to apply the configuration changes.
 +
 
 +
=== Enabling jails ===
 +
By default all jails are disabled. [[Append]] {{ic|1=enabled = true}} to the jail you want to use, e.g. to enable the [[OpenSSH]] jail:
 +
 
 +
{{hc|/etc/fail2ban/jail.local|2=
 +
[sshd]
 +
enabled = true
 +
}}
 +
 
 +
See [[#Custom SSH jail]].
 +
 
 +
=== Receive an alert e-mail ===
 +
 
 +
If you want to receive an e-mail when someone has been banned, you have to configure an SMTP client (e.g. [[msmtp]]) and change default action, as given below.
 +
 
 +
{{hc|/etc/fail2ban/jail.local|<nowiki>
 +
[DEFAULT]
 +
destemail = yourname@example.com
 +
sender = yourname@example.com
 +
 
 +
# to ban & send an e-mail with whois report to the destemail.
 +
action = %(action_mw)s
 +
 
 +
# same as action_mw but also send relevant log lines
 +
#action = %(action_mwl)s
 +
</nowiki>}}
 +
 
 +
=== Firewall and services ===
 +
 
 +
Most [[firewalls]] and services should work out of the box. See {{ic|/etc/fail2ban/action.d/}} for examples, e.g. [https://github.com/fail2ban/fail2ban/blob/master/config/action.d/ufw.conf ufw.conf].
 +
 
 +
== Tips and tricks ==
 +
 
 +
=== Custom SSH jail ===
 +
 
 +
{{Warning|If the attacker knows your IP address, they can send packets with a spoofed source header and get your IP address locked out of the server. [[SSH keys]] provide an elegant solution to the problem of brute forcing without these problems.}}
 +
 
 +
Edit {{ic|/etc/fail2ban/jail.d/sshd.local}}, add this section and update the list of trusted IP addresses in {{ic|ignoreip}}.
 +
 
 +
If your firewall is [[iptables]]:
 +
  [sshd]
 
  enabled  = true
 
  enabled  = true
 
  filter  = sshd
 
  filter  = sshd
  action  = iptables[name=SSH, port=ssh, protocol=tcp]                                       
+
  banaction = iptables
            sendmail-whois[name=SSH, dest=your@mail.org, sender=fail2ban@mail.com]
+
  backend = systemd
  logpath = /var/log/auth.log                                                                   
 
 
  maxretry = 5
 
  maxretry = 5
 +
findtime = 1d
 +
bantime  = 2w
 +
ignoreip = 127.0.0.1/8
 +
 +
fail2ban has IPv6 support since version 0.10. Adapt your firewall accordingly, e.g. start and enable {{ic|ip6tables.service}}.
 +
 +
{{Note|If your firewall is [[shorewall]], replace {{ic|iptables}} with {{ic|shorewall}}. You can also set {{ic|BLACKLIST}} to {{ic|ALL}} in {{ic|/etc/shorewall/shorewall.conf}}, otherwise the rule added to ban an IP address will affect only new connections.}}
 +
 +
{{Note|It may be necessary to set {{ic|LogLevel VERBOSE}} in {{ic|/etc/ssh/sshd_config}} to allow full fail2ban monitoring as otherwise password failures may not be logged correctly.}}
 +
 +
=== Service hardening ===
  
If your firewall is shorewall:
+
Currently, fail2ban must be run as ''root''. Therefore, you may wish to consider hardening the process with [[systemd]].
[ssh-shorewall]
+
 
enabled  = true
+
Create a [[Systemd#Drop-in files|drop-in]] configuration file for {{ic|fail2ban.service}}:
filter  = sshd
+
 
action  = shorewall
+
{{hc|/etc/systemd/system/fail2ban.service.d/override.conf|2=
            sendmail-whois[name=SSH, dest=your@mail.org, sender=fail2ban@mail.com]
+
[Service]
logpath  = /var/log/auth.log                                                                  
+
PrivateDevices=yes
maxretry = 5
+
PrivateTmp=yes
 +
ProtectHome=read-only
 +
ProtectSystem=strict
 +
NoNewPrivileges=yes
 +
ReadWritePaths=-/var/run/fail2ban
 +
ReadWritePaths=-/var/lib/fail2ban
 +
ReadWritePaths=-/var/log/fail2ban
 +
ReadWritePaths=-/var/spool/postfix/maildrop
 +
CapabilityBoundingSet=CAP_AUDIT_READ CAP_DAC_READ_SEARCH CAP_NET_ADMIN CAP_NET_RAW
 +
}}
 +
 
 +
The {{ic|CapabilityBoundingSet}} parameters {{ic|CAP_DAC_READ_SEARCH}} will allow fail2ban full read access to every directory and file, {{ic|CAP_NET_ADMIN}} and {{ic|CAP_NET_RAW}} allow setting of firewall rules with [[iptables]]. See {{man|7|capabilities}} for more info.
 +
 
 +
By using {{ic|1=ProtectSystem=strict}} the [[filesystem]] hierarchy will only be read-only, {{ic|ReadWritePaths}} allows fail2ban to have write access on required paths.
 +
 
 +
[[Create]] {{ic|/etc/fail2ban/fail2ban.local}} with the correct {{ic|logtarget}} path:
 +
{{hc|/etc/fail2ban/fail2ban.local|<nowiki>
 +
[Definition]
 +
logtarget = /var/log/fail2ban/fail2ban.log
 +
</nowiki>}}
  
{{Note|You can set {{Codeline|BLACKLISTNEWONLY}} to {{Codeline|No}} in {{Filename|/etc/shorewall/shorewall.conf}} otherwise the rule added to ban an IP address will affect only new connections.}}
+
Finally, [[Systemd#Using_units|reload systemd daemon]] to apply the changes of the unit and [[restart]] {{ic|fail2ban.service}}.
  
Also don't forget to add/change:
+
== See also ==
LogLevel VERBOSE
 
in your {{Filename|/etc/ssh/sshd_config}}. Else, password failures are not logged correctly.
 
  
==See also==
+
* [http://www.the-art-of-web.com/system/fail2ban-action-whitelist/ Using a Fail2Ban Jail to Whitelist a User]
*[[sshguard]]
+
* [http://www.the-art-of-web.com/system/fail2ban-filters/ Optimising your Fail2Ban filters]
 +
* [http://www.the-art-of-web.com/system/fail2ban-sendmail/ Fail2Ban and sendmail]
 +
* [http://www.the-art-of-web.com/system/fail2ban/ Fail2Ban and iptables]
 +
* [http://www.the-art-of-web.com/system/fail2ban-howto/ Fail2Ban 0.8.3 Howto]
 +
* [http://www.the-art-of-web.com/system/fail2ban-log/ Monitoring the fail2ban log]

Latest revision as of 12:25, 23 August 2018

Fail2ban scans log files (e.g. /var/log/httpd/error_log) and bans IPs that show the malicious signs like too many password failures, seeking for exploits, etc. Generally Fail2Ban is then used to update firewall rules to reject the IP addresses for a specified amount of time, although any arbitrary other action (e.g. sending an email) could also be configured.

Warning: Using an IP banning software will stop trivial attacks but it relies on an additional daemon and successful logging. Additionally, if the attacker knows your IP address, they can send packets with a spoofed source header and get your IP address banned. Make sure to specify your IP in ignoreip.

Installation

Install fail2ban.

Usage

Configure fail2ban and enable/start fail2ban.service.

fail2ban-client

The fail2ban-client allows monitoring jails (reload, restart, status, etc.), to view all available commands:

$ fail2ban-client

To view all enabled jails:

# fail2ban-client status

To check the status of a jail, e.g. for sshd:

# fail2ban-client status sshd
Status for the jail: sshd
|- Filter
|  |- Currently failed: 1
|  |- Total failed:     9
|  `- Journal matches:  _SYSTEMD_UNIT=sshd.service + _COMM=sshd
`- Actions
   |- Currently banned: 1
   |- Total banned:     1
   `- Banned IP list:   0.0.0.0

Configuration

Due to the possibility of the /etc/fail2ban/jail.conf file being overwritten or improved during a distribution update, it is recommended to Create /etc/fail2ban/jail.local file. For example to change default ban time to 1 day:

/etc/fail2ban/jail.local
[DEFAULT]
bantime = 1d

Or create separate name.local files under the /etc/fail2ban/jail.d directory, e.g. /etc/fail2ban/jail.d/sshd.local.

Restart fail2ban.service to apply the configuration changes.

Enabling jails

By default all jails are disabled. Append enabled = true to the jail you want to use, e.g. to enable the OpenSSH jail:

/etc/fail2ban/jail.local
[sshd]
enabled = true

See #Custom SSH jail.

Receive an alert e-mail

If you want to receive an e-mail when someone has been banned, you have to configure an SMTP client (e.g. msmtp) and change default action, as given below.

/etc/fail2ban/jail.local
[DEFAULT]
destemail = yourname@example.com
sender = yourname@example.com

# to ban & send an e-mail with whois report to the destemail.
action = %(action_mw)s

# same as action_mw but also send relevant log lines
#action = %(action_mwl)s

Firewall and services

Most firewalls and services should work out of the box. See /etc/fail2ban/action.d/ for examples, e.g. ufw.conf.

Tips and tricks

Custom SSH jail

Warning: If the attacker knows your IP address, they can send packets with a spoofed source header and get your IP address locked out of the server. SSH keys provide an elegant solution to the problem of brute forcing without these problems.

Edit /etc/fail2ban/jail.d/sshd.local, add this section and update the list of trusted IP addresses in ignoreip.

If your firewall is iptables:

[sshd]
enabled  = true
filter   = sshd
banaction = iptables
backend  = systemd
maxretry = 5
findtime = 1d
bantime  = 2w
ignoreip = 127.0.0.1/8

fail2ban has IPv6 support since version 0.10. Adapt your firewall accordingly, e.g. start and enable ip6tables.service.

Note: If your firewall is shorewall, replace iptables with shorewall. You can also set BLACKLIST to ALL in /etc/shorewall/shorewall.conf, otherwise the rule added to ban an IP address will affect only new connections.
Note: It may be necessary to set LogLevel VERBOSE in /etc/ssh/sshd_config to allow full fail2ban monitoring as otherwise password failures may not be logged correctly.

Service hardening

Currently, fail2ban must be run as root. Therefore, you may wish to consider hardening the process with systemd.

Create a drop-in configuration file for fail2ban.service:

/etc/systemd/system/fail2ban.service.d/override.conf
[Service]
PrivateDevices=yes
PrivateTmp=yes
ProtectHome=read-only
ProtectSystem=strict
NoNewPrivileges=yes
ReadWritePaths=-/var/run/fail2ban
ReadWritePaths=-/var/lib/fail2ban
ReadWritePaths=-/var/log/fail2ban
ReadWritePaths=-/var/spool/postfix/maildrop
CapabilityBoundingSet=CAP_AUDIT_READ CAP_DAC_READ_SEARCH CAP_NET_ADMIN CAP_NET_RAW

The CapabilityBoundingSet parameters CAP_DAC_READ_SEARCH will allow fail2ban full read access to every directory and file, CAP_NET_ADMIN and CAP_NET_RAW allow setting of firewall rules with iptables. See capabilities(7) for more info.

By using ProtectSystem=strict the filesystem hierarchy will only be read-only, ReadWritePaths allows fail2ban to have write access on required paths.

Create /etc/fail2ban/fail2ban.local with the correct logtarget path:

/etc/fail2ban/fail2ban.local
[Definition]
logtarget = /var/log/fail2ban/fail2ban.log

Finally, reload systemd daemon to apply the changes of the unit and restart fail2ban.service.

See also