Pourquoi fail2ban n'interdit-il pas cette attaque?

J'ai fail2ban installé pour interdire les tentatives de bruteforce sur le mot de passe ssh. Il existe des exigences commerciales pour ne pas désactiver l'authentification par mot de passe sur cette machine.

fail2ban a été installé en utilisant le même livre de recettes de chef qui interdit efficacement les attaques ssh sur d'autres machines. Il y a une prison ssh configurée:

# service fail2ban status
fail2ban-server (pid  5480) is running...
WARNING 'pidfile' not defined in 'Definition'. Using default one: '/var/run/fail2ban/fail2ban.pid'
Status
|- Number of jail:  1
`- Jail list:       ssh

L'interdiction manuelle des utilisateurs fonctionne:

# fail2ban-client set ssh banip 103.41.124.46

Mais il ne semble pas avoir banni quiconque automatiquement:

# cat /var/log/fail2ban.log
2014-11-20 18:23:47,069 fail2ban.server [67569]: INFO    Exiting Fail2ban
2014-11-20 18:44:59,202 fail2ban.server [5480]: INFO    Changed logging target to /var/log/fail2ban.log for Fail2ban v0.8.14
2014-11-20 18:44:59,213 fail2ban.jail   [5480]: INFO    Creating new jail 'ssh'
2014-11-20 18:44:59,214 fail2ban.jail   [5480]: INFO    Jail 'ssh' uses poller
2014-11-20 18:44:59,249 fail2ban.jail   [5480]: INFO    Initiated 'polling' backend
2014-11-20 18:44:59,270 fail2ban.filter [5480]: INFO    Added logfile = /var/log/secure
2014-11-20 18:44:59,271 fail2ban.filter [5480]: INFO    Set maxRetry = 6
2014-11-20 18:44:59,272 fail2ban.filter [5480]: INFO    Set findtime = 600
2014-11-20 18:44:59,272 fail2ban.actions[5480]: INFO    Set banTime = 300
2014-11-20 18:44:59,431 fail2ban.jail   [5480]: INFO    Jail 'ssh' started
2014-11-21 11:09:37,447 fail2ban.actions[5480]: WARNING [ssh] Ban 103.41.124.46
2014-11-21 11:10:32,602 fail2ban.actions[5480]: WARNING [ssh] Ban 122.225.97.75
2014-11-21 11:14:37,899 fail2ban.actions[5480]: WARNING [ssh] Unban 103.41.124.46
2014-11-21 11:15:32,976 fail2ban.actions[5480]: WARNING [ssh] Unban 122.225.97.75
2014-11-21 11:30:06,295 fail2ban.comm   [5480]: WARNING Command ['ban', 'ssh', '189.203.240.89'] has failed. Received Exception('Invalid command',)
2014-11-21 11:30:33,966 fail2ban.actions[5480]: WARNING [ssh] Ban 189.203.240.89
2014-11-21 11:35:34,303 fail2ban.actions[5480]: WARNING [ssh] Unban 189.203.240.89

Par exemple, il s'agit d'une attaque /var/log/messagesqui aurait dû être interceptée et interdite:

Nov 21 07:51:32 my_hostname sshd[51074]: Failed password for root from 122.225.109.219 port 1788 ssh2
Nov 21 07:51:34 my_hostname sshd[51072]: Failed password for root from 122.225.109.219 port 58285 ssh2
Nov 21 07:51:35 my_hostname sshd[51076]: Failed password for invalid user admin from 122.225.109.219 port 2221 ssh2
Nov 21 07:51:35 my_hostname sshd[51074]: Failed password for root from 122.225.109.219 port 1788 ssh2
Nov 21 07:51:37 my_hostname sshd[51072]: Failed password for root from 122.225.109.219 port 58285 ssh2
Nov 21 07:51:37 my_hostname sshd[51074]: Failed password for root from 122.225.109.219 port 1788 ssh2
Nov 21 07:51:38 my_hostname sshd[51076]: Failed password for invalid user admin from 122.225.109.219 port 2221 ssh2
Nov 21 07:51:38 my_hostname sshd[51084]: Failed password for root from 122.225.109.219 port 3501 ssh2
Nov 21 07:51:39 my_hostname sshd[51072]: Failed password for root from 122.225.109.219 port 58285 ssh2

Ceci est également connecté /var/log/secure:

Nov 25 16:06:40 cluster-122-1413591380-db sshd[75769]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:06:46 cluster-122-1413591380-db sshd[75769]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:06:48 cluster-122-1413591380-db sshd[75778]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:06:55 cluster-122-1413591380-db sshd[75778]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:06:57 cluster-122-1413591380-db sshd[75780]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:03 cluster-122-1413591380-db sshd[75780]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:05 cluster-122-1413591380-db sshd[75793]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:12 cluster-122-1413591380-db sshd[75793]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:13 cluster-122-1413591380-db sshd[75797]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:21 cluster-122-1413591380-db sshd[75797]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:22 cluster-122-1413591380-db sshd[75803]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:28 cluster-122-1413591380-db sshd[75803]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:29 cluster-122-1413591380-db sshd[75809]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:36 cluster-122-1413591380-db sshd[75809]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root
Nov 25 16:07:38 cluster-122-1413591380-db sshd[75811]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=103.41.124.41  user=root

Voici mon jail.local:

# Fail2Ban configuration file.
#
# The configuration here inherits from /etc/fail2ban/jail.conf. Any setting
# omitted here will take it's value from that file
#
# Author: Yaroslav O. Halchenko <snip>
#
#

# The DEFAULT allows a global definition of the options. They can be overridden
# in each jail afterwards.

[DEFAULT]

# "ignoreip" can be an IP address, a CIDR mask or a DNS host
ignoreip = 127.0.0.1/8
findtime = 600
bantime  = 300
maxretry = 5

# "backend" specifies the backend used to get files modification. Available
# options are "gamin", "polling" and "auto".
# yoh: For some reason Debian shipped python-gamin didn't work as expected
#      This issue left ToDo, so polling is default backend for now
backend = polling

#
# Destination email address used solely for the interpolations in
# jail.{conf,local} configuration files.
destemail = root@localhost

#
# ACTIONS
#

# Default banning action (e.g. iptables, iptables-new,
# iptables-multiport, shorewall, etc) It is used to define
# action_* variables. Can be overridden globally or per
# section within jail.local file
banaction = iptables-multiport

# email action. Since 0.8.1 upstream fail2ban uses sendmail
# MTA for the mailing. Change mta configuration parameter to mail
# if you want to revert to conventional 'mail'.
mta = sendmail

# Default protocol
protocol = tcp

# Specify chain where jumps would need to be added in iptables-* actions
chain = INPUT

#
# Action shortcuts. To be used to define action parameter

# The simplest action to take: ban only
action_ = %(banaction)s[name=%(__name__)s, port="%(port)s", protocol="%(protocol)s", chain="%(chain)s"]

# ban & send an e-mail with whois report to the destemail.
action_mw = %(banaction)s[name=%(__name__)s, port="%(port)s", protocol="%(protocol)s", chain="%(chain)s"]
              %(mta)s-whois[name=%(__name__)s, dest="%(destemail)s", protocol="%(protocol)s", chain="%(chain)s"]

# ban & send an e-mail with whois report and relevant log lines
# to the destemail.
action_mwl = %(banaction)s[name=%(__name__)s, port="%(port)s", protocol="%(protocol)s", chain="%(chain)s"]
               %(mta)s-whois-lines[name=%(__name__)s, dest="%(destemail)s", logpath=%(logpath)s, chain="%(chain)s"]

# Choose default action.  To change, just override value of 'action' with the
# interpolation to the chosen action shortcut (e.g.  action_mw, action_mwl, etc) in jail.local
# globally (section [DEFAULT]) or per specific section
action = %(action_)s

#
# JAILS
#

# Next jails can inherit from the configuration in /etc/fail2ban/jail.conf.
# Enable any defined in that file jail by including
#
# [SECTION_NAME]
# enabled = true
#
# Optionally you may override any other parameter (e.g. banaction,
# action, port, logpath, etc) in that section within jail.local


[ssh]

enabled = true
port = ssh
filter = sshd
logpath = /var/log/secure
maxretry = 6

[ssh-iptables]

enabled = false

Pourquoi fail2ban ne fonctionne-t-il pas? Alternativement, pourquoi n'a-t-il pas banni l'attaquant ci-dessus sans mon intervention manuelle?

Le paramètre logpathdoit être défini sur un chemin d'accès à un fichier journal dans lequel les tentatives SSH vont être enregistrées. Donc, si c'est le cas /var/log/messages, /var/log/securec'est évidemment incorrect.

Modifiez le logpathparamètre pour qu'il soit le fichier correct.

Sur RHEL et CentOS, les erreurs d'authentification vont à / var / log / messages ou / var / log secure:

# cat /etc/rsyslog.conf | grep auth
# Don't log private authentication messages!
*.info;mail.none;authpriv.none;cron.none                /var/log/messages
# The authpriv file has restricted access.
authpriv.*                                              /var/log/secure

Par défaut, sshd est configuré avec SyslogFacility défini sur AUTH, qui va dans / var / log / messages. Si vous remplacez / etc / ssh / sshd_config comme suit, il ira à la place dans / var / log / secure:

SyslogFacility AUTHPRIV

Je travaille avec des machines sur le cloud SoftLayer, et leur configuration d'image de base est passée de AUTHPRIV à AUTH l'année dernière.

Par défaut, fail2ban a la prison suivante dans /etc/fail2ban/jail.local:

[ssh]

enabled = true
port = ssh
filter = sshd
logpath = /var/log/secure
maxretry = 6

Je recommande d'ajouter une deuxième prison à /etc/fail2ban/jail.local:

[ssh-log-messages]

enabled = true
port = ssh
filter = sshd
logpath = /var/log/messages
maxretry = 6

Ensuite, redémarrez fail2ban pour que la deuxième prison prenne effet:

service fail2ban restart

Une autre approche consisterait à étendre l'expression régulière sshd dans /etc/fail2ban/filter.d/sshd.conf. Il y a suffisamment d'informations dans / var / log / secure et / var / log / messages pour interdire les adresses IP. Malheureusement, fail2ban ne peut pas analyser tous les messages sans ajouter une expression régulière alternative. Ceci est laissé comme exercice.