一 、安装 Fail2ban
服务下载rpmforge , 里面有大量最新的rpm包.
wget http://dag.wieers.com/rpm/packages/rpmforge-release/rpmforge-release-0.3.6-1.el5.rf.i386.rpm
rpm -ivh rpmforge-release-0.3.6-1.el5.rf.i386.rpm
开始yum吧～～！
yum install fail2ban
fail2ban noarch 0.8.2-3.el5.rf rpmforge 125 k
Installing for dependencies:
gamin
gamin-python
安装是十分简单的拉.
fail2ban 原理
fail2ban 调用 iptables 实时阻挡外界的攻击，按照你的要求在一段时间内找出符合条件的日志，然后动作。
二 、设定fail2ban服务
fail2ban 的设定档在这里
/etc/fail2ban
fail2ban.conf 日志设定文档
jail.conf 阻挡设定文档
/etc/fail2ban/filter.d 具体阻挡内容设定目录
三 、为何需要安装fail2ban呢？
Extmail 本身是没有邮件系统被攻击的解决方案，黑客是会不断user unknow地试探pop3 smtp 认证得到密码或电邮地址，大家可能问得到邮地址有何作用呢？电邮地址是可以贩卖的哦！而且十分值钱的，如果垃圾邮件者购买了这些地址，你的邮件服务器就有排忙了。
你话需不需要安装个fail2ban保护呢？
四 、实施保护
1. 保护 SSH 拦截
先看看fail2ban是如何拦截的？
cat /etc/fail2ban/filter.d/sshd.conf
failregex = ^%(__prefix_line)s(?:error: PAM: )?Authentication failure for .* from <HOST>s*$
^%(__prefix_line)sFailed [-/w]+ for .* from <HOST>(?: port d*)?(?: sshd*)?$
^%(__prefix_line)sROOT LOGIN REFUSED.* FROM <HOST>s*$
^%(__prefix_line)s[iI](?:llegal|nvalid) user .* from <HOST>s*$
^%(__prefix_line)sUser S+ from <HOST> not allowed because not listed in AllowUsers$
^%(__prefix_line)sauthentication failure; logname=S* uid=S* euid=S* tty=S* ruser=S* rhost=<HOST>(?:s+user=.*)?s*$
^%(__prefix_line)srefused connect from S+ (<HOST>)s*$
^%(__prefix_line)sAddress <HOST> .* POSSIBLE BREAK-IN ATTEMPTs*$
fail2ban 使用了正则表达式找出:
Authentication failure/authentication failure
ROOT LOGIN REFUSED
refused connect from
POSSIBLE BREAK-IN ATTEMPT
not allowed because not listed in AllowUsers
以上的状况，可以根据你实际要求删减. 其中<HOST> 为建立连接的IP
开启 SSH 拦截
vi /etc/fail2ban/jail.conf
[ssh-iptables]
enabled = true
filter = sshd
action = iptables[name=SSH, port=ssh, protocol=tcp]
sendmail-whois[name=SSH, dest=收件者电邮地址, sender=寄件者电邮地址]
logpath = /var/log/secure
maxretry = 3
findtime = 300
bantime = 86400
fail2ban 会按照你的要求去查看/var/log/secure日志文件,然后在findtime = 300 "5分钟" 之内符合条件
的记录下来，如果到达了maxretry = 3 "3次符合条件" 就阻挡这个IP连接22端口 bantime = 86400 "一天的时间".
2. POP3 保护拦截
cat /etc/fail2ban/filter.d/courierlogin.conf
failregex = LOGIN FAILED, .*, ip=[<HOST>]$
这里表示错误地输入用户名／密码的pop3连接.
开启 pop3 保护
vi /etc/fail2ban/jail.conf
[POP3]
enabled = true
filter = courierlogin
action = iptables[name=pop3, port=110, protocol=tcp]
logpath = /var/log/maillog
bantime = 1800
findtime = 300
maxretry = 15
大家应该懂得如何看了吧？ 我不写拉！好累。参数可以按照你实际要求修改噢～！
3. POP3-SSL 保护拦截
cat /etc/fail2ban/filter.d/courierlogin-ssl.conf
failregex = LOGIN FAILED, .*, ip=[<HOST>]$
这里表示错误地输入用户名／密码的pop3-ssl连接.
vi /etc/fail2ban/jail.conf
[POP3-SSL]
enabled = true
filter = courierlogin-ssl
action = iptables[name=pop3-ssl, port=995, protocol=tcp]
logpath = /var/log/maillog
bantime = 1800
findtime = 300
maxretry = 15
4 SMTP 保护拦截
cat /etc/fail2ban/filter.d/couriersmtp.conf
failregex = postfix/smtpd.* warning: unknown[<HOST>]: SASL LOGIN authentication failed: authentication failure
这里表示错误地输入用户名／密码的smtp连接.
vi /etc/fail2ban/jail.conf
[SMTP]
enabled = true
filter = couriersmtp
action = iptables[name=smtp, port=25:366, protocol=tcp]
logpath = /var/log/maillog
bantime = 1800
findtime = 300
maxretry = 15
参数可以按照你实际要求修改.
5. Extmail 登录保护
由于Extmail 的web mail 登入没有做到保护，现在加固吧！
vi /etc/fail2ban/filter.d/extmail.conf
failregex = extmail.*: user=.*, client=<HOST>, module=login, status=badlogin
这里表示错误地输入用户名／密码的web mail 登入.
vi /etc/fail2ban/jail.conf
[extmail]
enabled = true
filter = extmail
action = iptables[name=httpd, port=http, protocol=tcp]
logpath = /var/log/maillog
bantime = 300
findtime = 300
maxretry = 6
6. POSTFIX 保护User unknow 的试探.
不知道这个动作的意思先看看这篇文章。
http://hi.baidu.com/enjoyunix/blog/item/e8506058fd3c3189810a183a.html
vi /etc/fail2ban/filter.d/postfix.conf
failregex = reject: RCPT from (.*)[<HOST>]: 450
vi /etc/fail2ban/jail.conf
[POSTFIX]
enabled = true
filter = postfix
action = iptables[name=postfix, port=25, protocol=tcp]
logpath = /var/log/maillog
bantime = 43200
findtime = 1200
maxretry = 5
这里保护了User unknow 的试探以及垃圾邮件跳信攻击。
五 、看看iptables
iptables -L -nv
pkts bytes target prot opt in out source destination
0 0 fail2ban-pop3-ssl tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:995
773 83329 fail2ban-postfix tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:25
299 12660 fail2ban-pop3 tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:110
301 12740 fail2ban-ftp tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:21
3354 253K fail2ban-SSH tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22
438 33979 fail2ban-httpd tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 5703 packets, 829K bytes)
pkts bytes target prot opt in out source destination
Chain fail2ban-SSH (1 references)
pkts bytes target prot opt in out source destination
3354 253K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain fail2ban-ftp (1 references)
pkts bytes target prot opt in out source destination
301 12740 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain fail2ban-httpd (1 references)
pkts bytes target prot opt in out source destination
438 33979 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain fail2ban-pop3 (1 references)
pkts bytes target prot opt in out source destination
299 12660 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain fail2ban-pop3-ssl (1 references)
pkts bytes target prot opt in out source destination
0 0 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain fail2ban-postfix (1 references)
pkts bytes target prot opt in out source destination
773 83329 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain fail2ban-smtp (0 references)
pkts bytes target prot opt in out source destination
0 0 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
如何监察呢？
#watch -n 1 fail2ban-client status POSTFIX
Status for the jail: POSTFIX
|- filter
| |- File list: /var/log/maillog
| |- Currently failed: 2
| `- Total failed: 22
`- action
|- Currently banned: 0
| `- IP list:
`- Total banned: 0
看看那些垃圾邮件者真是好无聊！不断地试探我的邮件服务器呢。
六、 看看fail2ban的日志
# cat fail2ban.log | grep '] Ban '
2009-04-07 20:22:44,575 fail2ban.actions: WARNING [POSTFIX] Ban ip地址
就以看到过去有那些IP拦截了，以及是那个服务。
# cat fail2ban.log | grep '] Unban '
可以查看什么时候解的。