Fail2ban

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Fail2ban for SME Server

	Skill level: Easy
	The instructions on this page can be followed by a beginner.

Maintainer

Daniel B.
Firewall Services
mailto:daniel@firewall-services.com

Description

Fail2ban operates by monitoring log files (e.g. /var/log/pwdfail, /var/log/auth.log, etc.) for selected entries and running scripts based on them. Most commonly this is used to block selected IP addresses that may belong to hosts that are trying to breach the system's security. It can ban any host IP that makes too many login attempts or performs any other unwanted action within a time frame defined by the administrator. Fail2ban is typically set up to unban a blocked host within a certain period, so as to not "lock out" any genuine connections that may have been temporarily misconfigured. However, an unban time of several minutes is usually enough to stop a network connection being flooded by malicious connections, as well as reducing the likelihood of a successful dictionary attack.

	Tip:
	fail2ban is not only a tool against brute force attack on ssh but it can be a tool useful against http protocol attacks or spam attacks on your server. See the jail section

Requirements

This contrib has been developped and tested on SME Server 8 and later. It probably won't work on SME 7.

	Note:
	The SME feature AutoBlock SSH should be disabled to ensure that fail2ban controls SSH traffic and not the SME build-in firewall.

Installation sme8 and sme9

Configure Firewall-Services's repository:

db yum_repositories set fws repository \
BaseURL http://repo.firewall-services.com/centos/\$releasever \
EnableGroups no GPGCheck yes \
Name "Firewall Services" \
GPGKey http://repo.firewall-services.com/RPM-GPG-KEY \
Visible yes status disabled

Configure EPEL's repository: For SME 8.x,

/sbin/e-smith/db yum_repositories set epel repository \
Name 'Epel - EL5' \
BaseUrl 'http://download.fedoraproject.org/pub/epel/5/$basearch' \
MirrorList 'http://mirrors.fedoraproject.org/mirrorlist?repo=epel-5&arch=$basearch' \
EnableGroups no \
GPGCheck yes \
GPGKey http://dl.fedoraproject.org/pub/epel/RPM-GPG-KEY-EPEL \
Visible no \
status disabled

For SME 9.x,

/sbin/e-smith/db yum_repositories set epel repository \
Name 'Epel - EL6' \
BaseUrl 'http://download.fedoraproject.org/pub/epel/6/$basearch' \
MirrorList 'http://mirrors.fedoraproject.org/mirrorlist?repo=epel-6&arch=$basearch' \
EnableGroups no \
GPGCheck yes \
GPGKey http://dl.fedoraproject.org/pub/epel/RPM-GPG-KEY-EPEL \
Visible no \
status disabled

signal-event yum-modify

• install the rpms

yum --enablerepo=fws --enablerepo=epel install smeserver-fail2ban

• Appply the needed configuration:

expand-template /etc/rc.d/init.d/masq
/etc/init.d/masq restart
signal-event fail2ban-conf

or

signal-event post-upgrade; signal-event reboot

	Warning:
	Failing to run either of these command will completly lock network access next time iptables rules are reloaded

DB command

there is no panel yet you can manage the contrib by the db configuration, it is quite simple

# config show fail2ban 
fail2ban=service
   Mail=enabled
   status=enabled

Available options are below:

• IgnoreIP: a comma separated list of IP or CIDR networks which will never be blocked by fail2ban. Exemple: 12.15.22.4,17.20.0.0/16. All your local networks and networks allowed to access the server-manager are already automatically whitelisted
• FilterLocalNetworks can be enabled or disabled (default is disabled). If set to enabled, local networks won't be whitelisted, and fail2ban can also ban hosts from the internal networks. Note that networks allowed to access the server-manager are not affected (they will never be blocked)
• BanTime: Duration (in seconds) of a ban. Default to 1800
• FindTime: The window fail2ban will check, in seconds. Default is 900. So, this mean fail2ban will only check for the number of failed login attempts in the last 15 minuts
• MaxRetry: Number of failed attempts in the last FindTime seconds to trigger a ban. Default is 3
• Mail: can be enabled or disabled (default is enabled). If enabled, each ban will be notified by mail
• MailRecipient: if Mail is enabled, the email address which should receive ban notifications. Default is root (the admin account will receive)

After changing one of these settings, you need to apply it:

signal-event fail2ban-conf

for example :

config setprop fail2ban IgnoreIP 12.15.22.4,17.20.0.0/16
signal-event fail2ban-conf

Services

The following services are monitored, and fail2ban will ban client IP for BanTime if more than MaxRetry authentication failure occure in less than FindTime

• ssh
• dovecot (only on SME9, or if you run smeserver-dovecot)
• qpsmtpd. If a remote server send you too many mails which qpsmtpd rejects, it's probably spammer, so Fail2ban will blacklist it. MaxRetry is x3 for this service, so with the default config, a remote server will be blacklisted if 9 mails are rejected in less than 15 minutes
• httpd-e-smith. The standard http server. 3 different filters check apache logs:
  • noscripts: check client which ask for scripts which are not available on your server. It's usually script-kiddies trying to exploit security vulerabilities
  • scan: another set of filter for popular scans (phpMyAdmin, wp-login, admin area etc...)
  • auth: will check for standard authentication failure
• pam. This will check a generic authentication failure. Everything which uses pam should work
• SOGo. Check SOGo logs for failed authentications
• LemonLDAP-NG. Check system logs for auth failure on LemonLDAP::NG portal
• ftp. Check auth failure on your FTP daemon
• Ejabberd. Check auth failure against EJabberd

Each filters will disable itself if the corresponding service is disabled. You can also disable specific filter if you want. For example, if you want to disable Apache filters:

db configuration setprop httpd-e-smith Fail2Ban disabled
signal-event fail2ban-conf

Selective bans

Fail2Ban will do its best to do a selective ban. For example, if 3 auth failure against ssh are detected, only tcp port 22 (or any other port you choosed for SSH) will be blocked. Same for httpd-e-smith, SOGO, LemonLDAP::NG which will only blacklist tcp ports 80 and 443, qpsmtpd will block tcp ports 25 and 465, dovecot will block 143 and 993 etc...

There's only two ways to be completly locked (all port/protocol):

• pam. As this is a generic file, it's not possible to check which service was used when an auth failure occured, so the entire client IP will be blacklisted
• recidive. This is a special filter. It monitors fail2Ban logs, and blacklist client IP which gets locked several time. If a client is locked out 5 times in 24 hours, it'll be completly blacklisted for one full week

Use Fail2ban

List all jails

[root@sme8 ~]# fail2ban-client status 
Status
|- Number of jail:	10
`- Jail list:		http-overflows, http-noscript, http-auth, sogo, pam-generic, ssh-ddos, http-scan, ssh, qpsmtpd, recidive

List IP banned from a specific jail

[root@sme8 ~]# fail2ban-client status ssh

choose the specific jail with the command above which lists the Jail-list.

Play with a script which list How many ip are banned from all jails

nano /root/checklist_ban

#!/bin/bash
#lancer le script en sudo 
JAILS=$(fail2ban-client status | grep " Jail list:" | sed 's/`- Jail list:\t\t//g' | sed 's/,//g')
for j in $JAILS
do
echo "$j $(fail2ban-client status $j | grep " Currently banned:" | sed 's/   |- Currently banned:\t//g')"
done

chmod 700 /root/checklist_ban

to launch the script, do the following command:

/root/checklist_ban

Unban an IP

In certain case you would to unban an IP immediately because you don't want waste time to wait the automatic IP unban process of fail2ban. In first you you have to find the specific jail which has blocked you IP, you can refer to the mail that the admin user has received or you can list a specific jail.

fail2ban-client status qpsmtpd

Status for the jail: qpsmtpd
|- filter
|  |- File list:	/var/log/qpsmtpd/current /var/log/sqpsmtpd/current 
|  |- Currently failed:	5
|  `- Total failed:	119
`- action
   |- Currently banned:	1
   |  `- IP list:	93.17.128.20 
   `- Total banned:	1

If you want to know all you active jail, then do :

fail2ban-client status

Therefore you have to play with this command to unban your IP

fail2ban-client set qpsmtpd unbanip 93.17.128.20 

the generic command is :

fail2ban-client set JAIL unbanip MYIP

Jail.conf

The jail.conf is templated (/etc/e-smith/templates/etc/fail2ban/jail.conf) and the default file contains the configuration as below. You can add your own template of jail.conf at

/etc/e-smith/templates-custom/etc/fail2ban/jail.conf

if first time you need to create the folder for your custom template

mkdir -p  /etc/e-smith/templates-custom/etc/fail2ban/jail.conf

and do this to expland templates

expand-template /etc/rc.d/init.d/masq
/etc/init.d/masq restart
signal-event fail2ban-conf

default jail.conf

[DEFAULT]
ignoreip = 127.0.0.0/8 192.168.XXX.XXX 192.168.XXX.0/24
bantime  = 1800
findtime  = 900
maxretry = 3
usedns = yes
backend = auto

	Note:
	Your network and your server are in the list of ignored IP by fail2ban (see IgnoreIP)

[ssh]
enabled  = true
filter   = sshd
logpath  = /var/log/sshd/current
action   = smeserver-iptables[port="22",protocol=tcp,bantime=1800]
          smeserver-sendmail[name="SSH",dest=root]

[ssh-ddos]
enabled  = true
filter   = sshd-ddos
logpath  = /var/log/sshd/current
action   = smeserver-iptables[port="22",protocol=tcp,bantime=1800]
          smeserver-sendmail[name="SSH",dest=root]

[qpsmtpd]
enabled  = true
filter   = qpsmtpd
logpath  = /var/log/*qpsmtpd/current
maxretry = 9
action   = smeserver-iptables[port="25,465",protocol=tcp,bantime=1800]
          smeserver-sendmail[name="Qpsmtpd",dest=root]

[http-overflows]
enabled  = true
filter   = apache-overflows
logpath  = /var/log/httpd/error_log
action   = smeserver-iptables[port="80,443",protocol=tcp,bantime=1800]
          smeserver-sendmail[name="Apache (overflows)",dest=root]

[http-noscript]
enabled  = true
filter   = apache-noscript
logpath  = /var/log/httpd/error_log
action   = smeserver-iptables[port="80,443",protocol=tcp,bantime=1800]
          smeserver-sendmail[name="Apache (noscript)",dest=root]

[http-scan]
enabled  = true
filter   = apache-scan
logpath  = /var/log/httpd/error_log
action   = smeserver-iptables[port="80,443",protocol=tcp,bantime=1800]
          smeserver-sendmail[name="Apache (scan)",dest=root]

[http-auth]
enabled  = true
filter   = apache-auth
logpath  = /var/log/httpd/error_log
action   = smeserver-iptables[port="80,443",protocol=tcp,bantime=1800]
          smeserver-sendmail[name="Apache (auth)",dest=root]

[pam-generic]
enabled  = true
filter   = pam-generic
logpath  = /var/log/secure
maxretry = 6
action   = smeserver-iptables[bantime=1800]
          smeserver-sendmail[name="PAM generic",dest=root]

[recidive]
enabled  = true
filter   = recidive
logpath  = /var/log/fail2ban/daemon.log
bantime  = 604800
findtime = 86400
maxretry = 5
backend  = polling
action   = smeserver-iptables[bantime=604800]
          smeserver-sendmail[name="Recidive",dest=root]

With many thanks to the author for his work templating the install of Fail2Ban into SME8/9 here are some notes for introduction:

• F2B adds to SMEserver's own high security after SME has already reported forbidden access, file not found or a relaying denied error. F2B filters read appropriate logs and associated jails implement timed bans (by dropping all packets arriving from the culprit IP). Another F2B action sends a notifying email.

• Restarting the contrib clears existing bans but a suitable 'findtime' results in a reban. Be aware that the restart delay can be unexpectedly lengthy, I've noticed a variation of between a few seconds to one that extended to nearly 40 minutes! YMMV

• The 'out of the box' install's given filters are *already* completely capable of detecting most problems without any user templating being necessary.

• Parameters are passed using db commands. On my SME8.1 and with only www & email expectations (no SSH) I used:

db configuration setprop qpsmtpd Fail2Ban enabled

db configuration setprop httpd-e-smith Fail2Ban enabled

config setprop fail2ban MailRecipient root

config setprop fail2ban FindTime 1200

config setprop fail2ban BanTime 604800

config setprop fail2ban MaxRetry 1

signal-event fail2ban-conf

• don't use MaxTry=0 (apparently it is a special Perl value)

• required www triggers need to have appeared in /var/log/httpd/error_log

• required email triggers need to have appeared in /var/log/*qpsmtpd/current

I broke the master template by making the internal multipliers ($MaxRetry/$max) equivalent to unity.
The expanded jail.conf then showed only my own db command value for MaxRetry=1:
see /etc/e-smith/templates/ect/fail2ban/jail.conf/*

On installation and eventual configuration I have observed automatic immediate bans
for all 'relaying denied' email and iterations of semalt referer spam within 'findtime':-)

Uninstall

yum remove smeserver-fail2ban fail2ban

Bugs

Please raise bugs under the SME-Contribs section in bugzilla and select the smeserver-fail2ban component or use this link .