新近刚上的FTP备份服务器，例行检查/var/log/secure日志时，发现不少sshd和vsftpd失败认证信息，很明显有人想用暴力破解工具窃取密码，所以需要编写一个安全脚本防止。
脚本需求如下：此SHELL脚本放在crontab计划任务里，每隔6小时（此时间根据实际情况来定义）就去读取/var/log/secure脚本，取出里面恶意猜测IP，如果单位时间内（一星期）的连接数是高于一个阀值，例如100（此阀值也可以根据实际情况来定义），则将其加进/etc/hosts.deny黑名单里，如果低于此阀值，则无视此IP。
/var/log/secure里认证失败信息如下：
Nov 28 10:18:08 centos2 sshd[7556]: Connection closed by 222.216.30.109
Nov 28 10:18:08 centos2 sshd[7557]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=222.216.30.109 user=root
Nov 28 10:18:09 centos2 sshd[7559]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=222.216.30.109 user=root
Nov 28 10:18:10 centos2 sshd[7551]: Failed password for root from 222.216.30.109 port 2391 ssh2
Nov 28 10:18:10 centos2 sshd[7552]: Connection closed by 222.216.30.109
Nov 28 10:18:10 centos2 sshd[7553]: Failed password for root from 222.216.30.109 port 2397 ssh2
Nov 28 10:18:10 centos2 sshd[7554]: Connection closed by 222.216.30.109
Nov 28 10:18:11 centos2 sshd[7557]: Failed password for root from 222.216.30.109 port 2401 ssh2
Nov 28 10:18:11 centos2 sshd[7558]: Connection closed by 222.216.30.109
Nov 28 10:18:11 centos2 sshd[7559]: Failed password for root from 222.216.30.109 port 2403 ssh2
Nov 28 10:18:11 centos2 sshd[7560]: Connection closed by 222.216.30.109
Nov 28 10:37:01 centos2 vsftpd: pam_unix(vsftpd:auth): check pass; user unknown
Nov 28 10:37:01 centos2 vsftpd: pam_unix(vsftpd:auth): authentication failure; logname= uid=0 euid=0 tty=ftp ruser=hello rhost=centos1.cn7788.com
Nov 28 10:37:01 centos2 vsftpd: pam_succeed_if(vsftpd:auth): error retrieving information about user hello
Nov 28 10:37:19 centos2 vsftpd: pam_unix(vsftpd:auth): check pass; user unknown
Nov 28 10:37:19 centos2 vsftpd: pam_unix(vsftpd:auth): authentication failure; logname= uid=0 euid=0 tty=ftp ruser=yhc rhost=centos1.cn7788.com
Nov 28 10:37:19 centos2 vsftpd: pam_succeed_if(vsftpd:auth): error retrieving information about user yhc
Nov 28 10:37:36 centos2 vsftpd: pam_unix(vsftpd:auth): check pass; user unknown
Nov 28 10:37:36 centos2 vsftpd: pam_unix(vsftpd:auth): authentication failure; logname= uid=0 euid=0 tty=ftp ruser=yuhongchun rhost=centos1.cn7788.com
Nov 28 10:37:36 centos2 vsftpd: pam_succeed_if(vsftpd:auth): error retrieving information about user yuhongchun
Nov 28 10:42:44 centos2 vsftpd: pam_unix(vsftpd:auth): check pass; user unknown
Nov 28 10:42:44 centos2 vsftpd: pam_unix(vsftpd:auth): authentication failure; logname= uid=0 euid=0 tty=ftp ruser=yuhongchun rhost=114.112.169.70
Nov 28 10:42:44 centos2 vsftpd: pam_succeed_if(vsftpd:auth): error retrieving information about user yuhongchun
Nov 28 10:42:56 centos2 vsftpd: pam_unix(vsftpd:auth): check pass; user unknown
Nov 28 10:42:56 centos2 vsftpd: pam_unix(vsftpd:auth): authentication failure; logname= uid=0 euid=0 tty=ftp ruser=andrewyu rhost=114.112.169.70
Nov 28 10:42:56 centos2 vsftpd: pam_succeed_if(vsftpd:auth): error retrieving information about user andrewyu
我们观察下/var/log/secure文件轮询特征，如下所示：
[root@centos2 log]# ls -lsart secure.*
512 -rw------- 1 root root 516379 11-04 01:31 secure.4
660 -rw------- 1 root root 668192 11-11 00:05 secure.3
304 -rw------- 1 root root 306589 11-17 10:33 secure.2
484 -rw------- 1 root root 488620 11-25 02:33 secure.1
基本上，/var/log/secure文件是以星期为轮询周期的，如果对安全要求严格的朋友还可以本着“一个不放过”的原则来抓取上面的旧secure的恶意IP，然后扔进/etc/hosts.deny文件里。下面我们就们就要想办法高效的来抓取这些恶意IP，如果参考原始版本的SHELL脚本写法，，我们这里要抓取secure日志中的侦测vsftpd及sshd服务的IP地址，我们可以用如下命令，命令如下所示：
cat /var/log/secure | awk '/Failed/{print $$(NF-3)}'| sort| uniq -c| awk '{print $$2"="$$1;}'
很明显，这样是取不到vsftpd失败的IP值的，sshd日志失败信息跟vsftpd日志失败信息不一样，我写了几种awk混合sed的方法，测试了效率，感觉用awk脚本速度是最快的，大家也可以写几种，用time命令测试下；最后精简了下代码，完成了整个脚本，脚本内容如下所示：
#!/bin/bash
awk '{for(i=1;i<=NF;i++){if($$i ~ /rhost/)print substr($$i,7)}}' /var/log/secure | sort | uniq -c >/root/black.txt
DEFINE="100"
cat /root/black.txt | while read LINE
do
NUM=`echo $$LINE |awk '{print $$1}'`
host=`echo $$LINE |awk '{print $$2}'`
if [ $$NUM -gt $$DEFINE ];
then
grep $$host /etc/hosts.deny > /dev/null
if [ $$? -gt 0 ];
then
echo "sshd:$$host" >> /etc/hosts.deny
echo "vsftpd:$$host" >> /etc/hosts.deny
fi
fi
done
脚本运行一段时间后，我们可以观察此脚本涉及到的一些文件，如/root/black.txt，结果如下所示：
[root@centos2 ~]# cat /root/black.txt
2 113.17.144.156
4 114.112.51.208
4 114.112.69.170
169 118-163-227-50.hinet-ip.hinet.net
8 119.188.7.200
8 122.70.130.11
61 124.248.32.246
12 183.203.14.121
3 189.26.255.11
56 199.204.237.60
3 199.30.53.220
5 201.236.80.4
6 220.172.191.31
30 222.216.30.109
60 222.253.159.111
58 223.4.180.23
166 58.221.42.178
1 61.132.4.85
152 61.142.106.34
22 61.167.33.222
7 85.126.166.83
166 www.b-nets.com
/etc/hosts.deny脚本内容如下：
sshd:124.248.32.246
vsftpd:124.248.32.246
sshd:199.204.237.60
vsftpd:199.204.237.60
sshd:222.253.159.111
vsftpd:222.253.159.111
sshd:223.4.180.23
vsftpd:223.4.180.23
sshd:58.221.42.178
vsftpd:58.221.42.178
sshd:61.142.106.34
vsftpd:61.142.106.34
sshd:118-163-227-50.hinet-ip.hinet.net
vsftpd:118-163-227-50.hinet-ip.hinet.net
sshd:www.b-nets.com
vsftpd:www.b-nets.com
最后，我们将此shell脚本放进crontab 里，每间隔六小时就运行一次，命令如下：
* */6 * * * root /bin/bash /root/hostsdeny.sh >> /dev/null 2>&1
由于/var/log/secure日志是以星期为轮询的，此脚本执行频率可自行设定，如果感觉服务器被频繁侦测，执行频率间隔可设置短些，反之，可设置长些。
