当你的 Linux 服务器暴露在互联网之中，该服务器将会遭到互联网上的扫描软件进行扫描，并试图猜测SSH登录口令。

你会发现，每天会有多条SSH登录失败纪录。那些扫描工具将对你的服务器构成威胁，你必须设置复杂登录口令，并将尝试多次登录失败的IP给阻止掉，让其在一段时间内不能访问该服务器。

用DenyHosts可以阻止试图猜测SSH登录口令，它会分析/var/log/secure等日志文件，当发现同一IP在进行多次SSH密码尝试时就会记录IP到/etc/hosts.deny文件，从而达到自动屏蔽该IP的目的。

一、yum 安装 denyhosts

    yum install repe-release denyhosts -y

 

二、 查看 denyhosts 安装路径:

     rpm -ql denyhosts

这边说下几个比较重要的目录

该目录中主要存放计划任务，日志压缩 以及 chkconfig 和 service 启动的文档

/etc/cron.d/denyhosts

/etc/denyhosts.conf

/etc/logrotate.d/denyhosts

/etc/rc.d/init.d/denyhosts

/etc/sysconfig/denyhosts

/usr/bin/denyhosts-control

/usr/bin/denyhosts.py

该目录中主要存放 denyhosts 所拒绝及允许的一些主机信息

/var/lib/denyhosts

/var/lib/denyhosts/allowed-hosts

/var/lib/denyhosts/allowed-warned-hosts

/var/lib/denyhosts/hosts

/var/lib/denyhosts/hosts-restricted

/var/lib/denyhosts/hosts-root

/var/lib/denyhosts/hosts-valid

/var/lib/denyhosts/offset

/var/lib/denyhosts/suspicious-logins

/var/lib/denyhosts/sync-hosts

/var/lib/denyhosts/users-hosts

/var/lib/denyhosts/users-invalid

/var/lib/denyhosts/users-valid

/var/log/denyhosts

 

     cp /etc/denyhosts.conf.bak /etc/denyhosts.conf

  egrep -v "(^$|^#)" /etc/denyhosts.conf.bak>/etc/denyhosts.conf

三，denyhost主配置文件/etc/denyhosts.conf 中的配置参数内容：

   

############ THESE SETTINGS ARE REQUIRED ############# 系统安全日志文件，主要获取ssh信息SECURE_LOG = /var/log/secure# 拒绝写入IP文件 hosts.deny HOSTS_DENY = /etc/hosts.deny # #过多久后清除已经禁止的，其中w代表周，d代表天，h代表小时，s代表秒，m代表分钟 PURGE_DENY = 4w # denyhosts所要阻止的服务名称 BLOCK_SERVICE = sshd # 允许无效用户登录失败的次数 DENY_THRESHOLD_INVALID = 3 # 允许普通用户登录失败的次数 DENY_THRESHOLD_VALID = 10 # 允许ROOT用户登录失败的次数 DENY_THRESHOLD_ROOT = 6 # 设定 deny host 写入到该资料夹 DENY_THRESHOLD_RESTRICTED = 1 # 将deny的host或ip纪录到Work_dir中 WORK_DIR = /var/lib/denyhosts SUSPICIOUS_LOGIN_REPORT_ALLOWED_HOSTS=YES # 是否做域名反解 HOSTNAME_LOOKUP=YES # 将DenyHOts启动的pid纪录到LOCK_FILE中，已确保服务正确启动，防止同时启动多个服务 LOCK_FILE = /var/lock/subsys/denyhosts ############ THESE SETTINGS ARE OPTIONAL ############ # 管理员Mail地址 ADMIN_EMAIL = root SMTP_HOST = localhost SMTP_PORT = 25 SMTP_FROM = DenyHosts 
    
      SMTP_SUBJECT = DenyHosts Report from $[HOSTNAME] # 有效用户登录失败计数归零的时间 AGE_RESET_VALID=5d # ROOT用户登录失败计数归零的时间 AGE_RESET_ROOT=25d # 用户的失败登录计数重置为0的时间(/usr/share/denyhosts/restricted-usernames) AGE_RESET_RESTRICTED=25d # 无效用户登录失败计数归零的时间 AGE_RESET_INVALID=10d ######### THESE SETTINGS ARE SPECIFIC TO DAEMON MODE ########## # denyhosts log文件 DAEMON_LOG = /var/log/denyhosts DAEMON_SLEEP = 30s # 该项与PURGE_DENY 设置成一样，也是清除hosts.deniedssh 用户的时间 DAEMON_PURGE = 1h
    

 四，启动 denyhosts 服务并查看状态

[root@test scripts]# /etc/init.d/denyhosts status

denyhosts.py 已停

[root@test scripts]# /etc/init.d/denyhosts start

启动 denyhosts：

五、通过测试 invalid、valid、root 等用户设置不同的ssh连接失败次数，来测试 denyhosts

      我们允许 invalid 用户只能失败5次、ROOT 用户失败1次、valid用户失败3次

   DENY_THRESHOLD_INVALID = 5

   DENY_THRESHOLD_VALID = 13

   DENY_THRESHOLD_ROOT = 1

简单的测试脚本：[root@test scripts]# cat see_denyhosts.sh

  echo -n "">/var/log/secure

 tail -f /var/log/secure

 tail -f /etc/hosts.deny

查看 /var/log/secure的日志信息

[root@test scripts]# tail -f /var/log/secure

May  8 15:01:21 test sshd[1764]: Failed password for root from 10.0.0.51 port 47358 ssh2

May  8 15:01:23 test sshd[1764]: Failed password for root from 10.0.0.51 port 47358 ssh2

May  8 15:01:24 test sshd[1764]: Failed password for root from 10.0.0.51 port 47358 ssh2

May  8 15:01:24 test sshd[1765]: Connection closed by 10.0.0.51

May  8 15:01:27 test sshd[1766]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=10.0.0.51  user=root

May  8 15:01:28 test sshd[1766]: Failed password for root from 10.0.0.51 port 47360 ssh2

May  8 15:01:33 test sshd[1766]: Failed password for root from 10.0.0.51 port 47360 ssh2

May  8 15:01:37 test sshd[1766]: Failed password for root from 10.0.0.51 port 47360 ssh2

May  8 15:01:37 test sshd[1767]: Connection closed by 10.0.0.51

May  8 15:01:37 test sshd[1766]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=10.0.0.51  user=root

/etc/hosts.deny文件的信息：

[root@test scripts]# cat /etc/hosts.deny

#

# hosts.deny    This file contains access rules which are used to

#        deny connections to network services that either use

#        the tcp_wrappers library or that have been

#        started through a tcp_wrappers-enabled xinetd.

#

#        The rules in this file can also be set up in

#        /etc/hosts.allow with a 'deny' option instead.

#

#        See 'man 5 hosts_options' and 'man 5 hosts_access'

#        for information on rule syntax.

#        See 'man tcpd' for information on tcp_wrappers

  rsync:ALL

# DenyHosts: Tue May  8 12:53:47 2018 | sshd: 10.0.0.7

[root@test scripts]# cat /etc/hosts.deny

#

# hosts.deny    This file contains access rules which are used to

#        deny connections to network services that either use

#        the tcp_wrappers library or that have been

#        started through a tcp_wrappers-enabled xinetd.

#

#        The rules in this file can also be set up in

#        /etc/hosts.allow with a 'deny' option instead.

#

#        See 'man 5 hosts_options' and 'man 5 hosts_access'

#        for information on rule syntax.

#        See 'man tcpd' for information on tcp_wrappers

  rsync:ALL

# DenyHosts: Tue May  8 12:53:47 2018 | sshd: 10.0.0.7

sshd: 10.0.0.7 ：表示已经禁止ip为10.0.0.7通过ssh服务连接本地服务器了

[root@web01 ~]# ssh anonymous@10.0.0.100

ssh_exchange_identification: Connection closed by remote host

 

六、关于清除及添加可信主机记录

      如果想删除一个已经禁止的主机IP，可以在/etc/hosts.deny文件中删除被禁的ip，

但做好的做法是以下操作：

1、停止DenyHosts服务：service denyhosts stop

2、在 /etc/hosts.deny 中删除你想取消的主机IP

3、编辑 DenyHosts 工作目录的所有文件 /var/lib/denyhosts，并且删除已被添加的主机信息。

/var/lib/denyhosts/hosts

/var/lib/denyhosts/hosts-restricted

/var/lib/denyhosts/hosts-root

/var/lib/denyhosts/hosts-valid

/var/lib/denyhosts/users-hosts

/var/lib/denyhosts/users-invalid

/var/lib/denyhosts/users-valid

七，关于你不想被denyhosts服务访问禁止登陆的主机

1，添加你想允许的主机IP地址到

/var/lib/denyhosts/allowed-hosts

2，启动DenyHosts服务： service denyhosts start

 

八，将denyhosts服务加入开机自启动中

  [root@test denyhosts]# chkconfig denyhosts on

在/etc/rc.local中加入如下内容：

  /etc/init.d/denyhosts start

说明：denyhosts服务可以防止服务器受到外网的攻击。