使用DenyHosts保护服务器安全
在几个月前，笔者介绍了一种保护服务器安全的方法 自动禁止攻击IP登陆SSH，保护服务器安全。这种方法需要自己去动手写相应的脚本，今天要介绍的是开源的脚本实现。
DenyHosts介绍
DenyHosts是一个脚本，旨在由Linux系统管理员运行，以帮助阻止SSH服务器攻击（也称为基于字典的攻击和蛮力攻击）。
如果你曾经看过你的SSH日志（Redhat上的/var/log/ secure，Mandrake上的/var/log/auth.log等等），你可能会惊讶地发现有多少黑客试图访问你的服务器。希望他们都没有成功（但是再一次，你怎么知道？）。自动防止攻击者继续进入你的系统不是更好吗？DenyHosts试图解决以上问题。
以上介绍来自官网。
安装
以下配置项都是基于centos7，读者如果是别的版本，准备工作可能略有不同。
如果你不需要了解你安装的都是什么，章节的最后有快速安装命令。
安装EPEL源
有些服务器安装的centos是简版，没有额外的软件包，那么需要先配置EPEL源。
yum update -y
yum install epel-release -y安装rsyslog
你需要确认你的centos服务器上有/var/log/secure这个文件，如果没有或者文件内容没有变化，说明没有安装系统日志服务。
yum install rsyslog -y安装DenyHosts
前面准备工作做好了，安装就很简单。
yum install denyhosts -y后续操作
需要重启系统日志服务和denyhosts。
systemctl restart rsyslog
systemctl restart denyhosts相关配置
编辑/etc/denyhosts.conf文件。
############ THESE SETTINGS ARE REQUIRED ############
########################################################################
#
# SECURE_LOG: the log file that contains sshd logging info
# if you are not sure, grep "sshd:" /var/log/*
#
# The file to process can be overridden with the --file command line
# argument
#
# Redhat or Fedora Core:
SECURE_LOG = /var/log/secure # centos系统的ssh登录日志文件位置
#
# Mandrake, FreeBSD or OpenBSD:
#SECURE_LOG = /var/log/auth.log
#
# SuSE:
#SECURE_LOG = /var/log/messages
#
# Mac OS X (v10.4 or greater -
# also refer to: http://www.denyhost.net/faq.html#macos
#SECURE_LOG = /private/var/log/asl.log
#
# Mac OS X (v10.3 or earlier):
#SECURE_LOG=/private/var/log/system.log
#
# Debian and Ubuntu
#SECURE_LOG = /var/log/auth.log
########################################################################
########################################################################
#
# HOSTS_DENY: the file which contains restricted host access information
#
# Most operating systems:
HOSTS_DENY = /etc/hosts.deny # 指定不给哪些IP提供服务
#
# Some BSD (FreeBSD) Unixes:
#HOSTS_DENY = /etc/hosts.allow
#
# Another possibility (also see the next option):
#HOSTS_DENY = /etc/hosts.evil
#######################################################################
########################################################################
#
# PURGE_DENY: removed HOSTS_DENY entries that are older than this time
# when DenyHosts is invoked with the --purge flag
#
# format is: i[dhwmy]
# Where 'i' is an integer (eg. 7)
# 'm' = minutes
# 'h' = hours
# 'd' = days
# 'w' = weeks
# 'y' = years
#
# never purge:
PURGE_DENY = # 这样设置意味着一旦被拉入黑名单，永远不会放出来
#
# purge entries older than 1 week
#PURGE_DENY = 1w
#
# purge entries older than 5 days
#PURGE_DENY = 5d
#
# For the default Fedora install, we want timestamping but no
# expiration (at least by default) so this is deliberately set high.
# Adjust to taste.
#PURGE_DENY = 4w
#######################################################################
#######################################################################
#
# PURGE_THRESHOLD: defines the maximum times a host will be purged.
# Once this value has been exceeded then this host will not be purged.
# Setting this parameter to 0 (the default) disables this feature.
#
# default: a denied host can be purged/re-added indefinitely
#PURGE_THRESHOLD = 0
#
# a denied host will be purged at most 2 times.
#PURGE_THRESHOLD = 2
#
#######################################################################
#######################################################################
#
# BLOCK_SERVICE: the service name that should be blocked in HOSTS_DENY
#
# man 5 hosts_access for details
#
# eg. sshd: 127.0.0.1 # will block sshd logins from 127.0.0.1
#
# To block all services for the offending host:
BLOCK_SERVICE = ALL # 这样设置意味着一旦进入黑名单，就所有服务都不提供
# To block only sshd:
#BLOCK_SERVICE = sshd
# To only record the offending host and nothing else (if using
# an auxilary file to list the hosts). Refer to:
# http://denyhost.sourceforge.net/faq.html#aux
#BLOCK_SERVICE =
#
#######################################################################
#######################################################################
#
# DENY_THRESHOLD_INVALID: block each host after the number of failed login
# attempts has exceeded this value. This value applies to invalid
# user login attempts (eg. non-existent user accounts)
#
DENY_THRESHOLD_INVALID = 1 # 对于不存在的用户，只允许失败一次
#
#######################################################################
#######################################################################
#
# DENY_THRESHOLD_VALID: block each host after the number of failed
# login attempts has exceeded this value. This value applies to valid
# user login attempts (eg. user accounts that exist in /etc/passwd) except
# for the "root" user
#
DENY_THRESHOLD_VALID = 3 # 对于普通用户，最多允许失败三次
#
#######################################################################
#######################################################################
#
# DENY_THRESHOLD_ROOT: block each host after the number of failed
# login attempts has exceeded this value. This value applies to
# "root" user login attempts only.
#
DENY_THRESHOLD_ROOT = 2 # 对于root用户只允许失败两次
#
#######################################################################
#######################################################################
#
# DENY_THRESHOLD_RESTRICTED: block each host after the number of failed
# login attempts has exceeded this value. This value applies to
# usernames that appear in the WORK_DIR/restricted-usernames file only.
#
DENY_THRESHOLD_RESTRICTED = 1
#
#######################################################################
#######################################################################
#
# WORK_DIR: the path that DenyHosts will use for writing data to
# (it will be created if it does not already exist).
#
# Note: it is recommended that you use an absolute pathname
# for this value (eg. /home/foo/denyhost/data)
#
WORK_DIR = /var/lib/denyhosts
#
#######################################################################
#######################################################################
#
# ETC_DIR: the path that DenyHosts will use for reading data when
# we need configuration information.
#
# Note: it is recommended that you use an absolute pathname
# for this value (eg. /etc or /usr/local/etc)
#
ETC_DIR = /etc
#
#######################################################################
#######################################################################
#
# SUSPICIOUS_LOGIN_REPORT_ALLOWED_HOSTS
#
# SUSPICIOUS_LOGIN_REPORT_ALLOWED_HOSTS=YES|NO
# If set to YES, if a suspicious login attempt results from an allowed-host
# then it is considered suspicious. If this is NO, then suspicious logins
# from allowed-hosts will not be reported. All suspicious logins from
# ip addresses that are not in allowed-hosts will always be reported.
#
SUSPICIOUS_LOGIN_REPORT_ALLOWED_HOSTS=YES
######################################################################
######################################################################
#
# HOSTNAME_LOOKUP
#
# HOSTNAME_LOOKUP=YES|NO
# If set to YES, for each IP address that is reported by Denyhosts,
# the corresponding hostname will be looked up and reported as well
# (if available).
#
HOSTNAME_LOOKUP=NO
#
######################################################################
######################################################################
#
# LOCK_FILE
#
# LOCK_FILE=/path/denyhosts
# If this file exists when DenyHosts is run, then DenyHosts will exit
# immediately. Otherwise, this file will be created upon invocation
# and deleted upon exit. This ensures that only one instance is
# running at a time.
#
# Redhat/Fedora:
LOCK_FILE = /var/lock/subsys/denyhosts
#
# Debian
#LOCK_FILE = /var/run/denyhosts.pid
#
# Misc
#LOCK_FILE = /tmp/denyhosts.lock
#
######################################################################
############ THESE SETTINGS ARE OPTIONAL ############
#######################################################################
#
# IPTABLES: if you would like DenyHost to block incoming connections
# using the Linux firewall IPTABLES, then set the following variable
# to the path of the iptables executable. Typically this is
# /sbin/iptables
# If this option is not set or commented out then the iptables
# firewall is not used.
#IPTABLES = /sbin/iptables
#
# Warning: If you are running IPTABLES, please make sure to comment
# out the PFCTL_PATH and the PF_TABLE variables below. PF and
# IPTABLES should not be running together on the same operating system.
#
# By default DenyHost will ask IPTables to block incoming connections
# from an aggressive host on ALL ports. While this is usually a good
# idea, it may prevent some botted machines from being able to access
# services their legitmate users want, like a web server. To only
# block specific ports, enable the following option.
# BLOCKPORT = 22
#
#######################################################################
#######################################################################
#
# On FreeBSD/OpenBSD/TrueOS/PC-BSD/NetBSD we may want to block incoming
# traffic using the PF firewall instead of the hosts.deny file
# (aka tcp_wrapper).
# The admin can set up a PF table that is persistent
# and DenyHost can add new addresses to be blocked to that table.
# The TrueOS operating system enables this by default, blocking
# all addresses in the "blacklist" table.
#
# To have DenyHost update the blocking PF table in real time, uncomment
# these next two options. Make sure the table name specificed
# is one created in the pf.conf file of your operating system.
# The PFCTL_PATH variable must point to the pfctl extectuable on your OS.
# PFCTL_PATH = /sbin/pfctl
# PF_TABLE = blacklist
# Note, a good rule to have in your pf.conf file to enable the
# blacklist table is:
#
# table <blacklist> persist file "/etc/blacklist"
# block from <blacklist> to any
#
# Warning: If you are using PF, please make sure to disable the
# IPTABLES rule above as these two packet filters should not be
# run together on the same operating system.
# Note: Even if you decide to run DenyHost with PF filtering
# only and no hosts.deny support, please still create an empty
# file called /etc/hosts.deny for backward compatibility.
# Also, please make sure PF is enabled prior to launching
# DenyHosts. To do this run "pfctl -e".
#######################################################################
#######################################################################
#
# ADMIN_EMAIL: if you would like to receive emails regarding newly
# restricted hosts and suspicious logins, set this address to
# match your email address. If you do not want to receive these reports
# leave this field blank (or run with the --noemail option)
#
# Multiple email addresses can be delimited by a comma, eg:
# ADMIN_EMAIL = foo@bar.com, bar@foo.com, etc@foobar.com
#
ADMIN_EMAIL = root@localhost
#
#######################################################################
#######################################################################
#
# SMTP_HOST and SMTP_PORT: if DenyHosts is configured to email
# reports (see ADMIN_EMAIL) then these settings specify the
# email server address (SMTP_HOST) and the server port (SMTP_PORT)
#
#
SMTP_HOST = localhost
SMTP_PORT = 25
#
#######################################################################
#######################################################################
#
# SMTP_USERNAME and SMTP_PASSWORD: set these parameters if your
# smtp email server requires authentication
#
#SMTP_USERNAME=foo
#SMTP_PASSWORD=bar
#
######################################################################
#######################################################################
#
# SMTP_FROM: you can specify the "From:" address in messages sent
# from DenyHosts when it reports thwarted abuse attempts
#
SMTP_FROM = DenyHosts <nobody@localhost>
#
#######################################################################
#######################################################################
#
# SMTP_SUBJECT: you can specify the "Subject:" of messages sent
# by DenyHosts when it reports thwarted abuse attempts
SMTP_SUBJECT = DenyHosts Report from $[HOSTNAME]
#
######################################################################
######################################################################
#
# SMTP_DATE_FORMAT: specifies the format used for the "Date:" header
# when sending email messages.
#
# for possible values for this parameter refer to: man strftime
#
# the default:
#
#SMTP_DATE_FORMAT = %a, %d %b %Y %H:%M:%S %z
#
######################################################################
######################################################################
#
# SYSLOG_REPORT
#
# SYSLOG_REPORT=YES|NO
# If set to yes, when denied hosts are recorded the report data
# will be sent to syslog (syslog must be present on your system).
# The default is: NO
#
#SYSLOG_REPORT=NO
#
#SYSLOG_REPORT=YES
#
######################################################################
######################################################################
#
# ALLOWED_HOSTS_HOSTNAME_LOOKUP
#
# ALLOWED_HOSTS_HOSTNAME_LOOKUP=YES|NO
# If set to YES, for each entry in the WORK_DIR/allowed-hosts file,
# the hostname will be looked up. If your versions of tcp_wrappers
# and sshd sometimes log hostnames in addition to ip addresses
# then you may wish to specify this option.
#
ALLOWED_HOSTS_HOSTNAME_LOOKUP=NO
#
######################################################################
######################################################################
#
# AGE_RESET_VALID: Specifies the period of time between failed login
# attempts that, when exceeded will result in the failed count for
# this host to be reset to 0. This value applies to login attempts
# to all valid users (those within /etc/passwd) with the
# exception of root. If not defined, this count will never
# be reset.
#
# See the comments in the PURGE_DENY section (above)
# for details on specifying this value or for complete details
# refer to: http://denyhost.sourceforge.net/faq.html#timespec
#
AGE_RESET_VALID=5d
#
######################################################################
######################################################################
#
# AGE_RESET_ROOT: Specifies the period of time between failed login
# attempts that, when exceeded will result in the failed count for
# this host to be reset to 0. This value applies to all login
# attempts to the "root" user account. If not defined,
# this count will never be reset.
#
# See the comments in the PURGE_DENY section (above)
# for details on specifying this value or for complete details
# refer to: http://denyhost.sourceforge.net/faq.html#timespec
#
AGE_RESET_ROOT=25d
#
######################################################################
######################################################################
#
# AGE_RESET_RESTRICTED: Specifies the period of time between failed login
# attempts that, when exceeded will result in the failed count for
# this host to be reset to 0. This value applies to all login
# attempts to entries found in the WORK_DIR/restricted-usernames file.
# If not defined, the count will never be reset.
#
# See the comments in the PURGE_DENY section (above)
# for details on specifying this value or for complete details
# refer to: http://denyhost.sourceforge.net/faq.html#timespec
#
AGE_RESET_RESTRICTED=25d
#
######################################################################
######################################################################
#
# AGE_RESET_INVALID: Specifies the period of time between failed login
# attempts that, when exceeded will result in the failed count for
# this host to be reset to 0. This value applies to login attempts
# made to any invalid username (those that do not appear
# in /etc/passwd). If not defined, count will never be reset.
#
# See the comments in the PURGE_DENY section (above)
# for details on specifying this value or for complete details
# refer to: http://denyhost.sourceforge.net/faq.html#timespec
#
AGE_RESET_INVALID=10d
#
######################################################################
######################################################################
#
# RESET_ON_SUCCESS: If this parameter is set to "yes" then the
# failed count for the respective ip address will be reset to 0
# if the login is successful.
#
# The default is RESET_ON_SUCCESS = no
#
#RESET_ON_SUCCESS = yes
#
#####################################################################
######################################################################
#
# PLUGIN_DENY: If set, this value should point to an executable
# program that will be invoked when a host is added to the
# HOSTS_DENY file. This executable will be passed the host
# that will be added as its only argument.
#
#PLUGIN_DENY=/usr/bin/true
#
######################################################################
######################################################################
#
# PLUGIN_PURGE: If set, this value should point to an executable
# program that will be invoked when a host is removed from the
# HOSTS_DENY file. This executable will be passed the host
# that is to be purged as it's only argument.
#
#PLUGIN_PURGE=/usr/bin/true
#
# The following plugin will restore the file contexts on /etc/hosts.deny after
# denyhosts purges old entries. This prevents breakage when selinux is set to
# enforcing mode, but still has a small window where the context is set
# incorrectly. The correct place to fix this is in the selinux policy.
#
#PLUGIN_PURGE=/usr/share/denyhosts/plugins/restorecon.sh
#
######################################################################
######################################################################
#
# USERDEF_FAILED_ENTRY_REGEX: if set, this value should contain
# a regular expression that can be used to identify additional
# hackers for your particular ssh configuration. This functionality
# extends the built-in regular expressions that DenyHosts uses.
# This parameter can be specified multiple times.
# See this faq entry for more details:
# http://denyhost.sf.net/faq.html#userdef_regex
#
#USERDEF_FAILED_ENTRY_REGEX=
#
#
######################################################################
######### THESE SETTINGS ARE SPECIFIC TO DAEMON MODE ##########
#######################################################################
#
# DAEMON_LOG: when DenyHosts is run in daemon mode (--daemon flag)
# this is the logfile that DenyHosts uses to report its status.
# To disable logging, leave blank. (default is: /var/log/denyhosts)
#
DAEMON_LOG = /var/log/denyhosts
#
# disable logging:
#DAEMON_LOG =
#
######################################################################
#######################################################################
#
# DAEMON_LOG_TIME_FORMAT: when DenyHosts is run in daemon mode
# (--daemon flag) this specifies the timestamp format of
# the DAEMON_LOG messages (default is the ISO8061 format:
# ie. 2005-07-22 10:38:01,745)
#
# for possible values for this parameter refer to: man strftime
#
# Jan 1 13:05:59
#DAEMON_LOG_TIME_FORMAT = %b %d %H:%M:%S
#
# Jan 1 01:05:59
#DAEMON_LOG_TIME_FORMAT = %b %d %I:%M:%S
#
######################################################################
#######################################################################
#
# DAEMON_LOG_MESSAGE_FORMAT: when DenyHosts is run in daemon mode
# (--daemon flag) this specifies the message format of each logged
# entry. By default the following format is used:
#
# %(asctime)s - %(name)-12s: %(levelname)-8s %(message)s
#
# Where the "%(asctime)s" portion is expanded to the format
# defined by DAEMON_LOG_TIME_FORMAT
#
# This string is passed to python's logging.Formatter contstuctor.
# For details on the possible format types please refer to:
# http://docs.python.org/lib/node357.html
#
# This is the default:
#DAEMON_LOG_MESSAGE_FORMAT = %(asctime)s - %(name)-12s: %(levelname)-8s %(message)s
#
#
######################################################################
#######################################################################
#
# DAEMON_SLEEP: when DenyHosts is run in daemon mode (--daemon flag)
# this is the amount of time DenyHosts will sleep between polling
# the SECURE_LOG. See the comments in the PURGE_DENY section (above)
# for details on specifying this value or for complete details
# refer to: http://denyhost.sourceforge.net/faq.html#timespec
#
#
DAEMON_SLEEP = 30s
#
#######################################################################
#######################################################################
#
# DAEMON_PURGE: How often should DenyHosts, when run in daemon mode,
# run the purge mechanism to expire old entries in HOSTS_DENY
# This has no effect if PURGE_DENY is blank.
#
DAEMON_PURGE = 1h
#
#######################################################################
######### THESE SETTINGS ARE SPECIFIC TO ##########
######### DAEMON SYNCHRONIZATION ##########
#######################################################################
#
# Synchronization mode allows the DenyHosts daemon the ability
# to periodically send and receive denied host data such that
# DenyHosts daemons worldwide can automatically inform one
# another regarding banned hosts. This mode is disabled by
# default, you must uncomment SYNC_SERVER to enable this mode.
#
# for more information, please refer to:
# http:/denyhost.sourceforge.net/faq.html
#
#######################################################################
#######################################################################
#
# SYNC_SERVER: The central server that communicates with DenyHost
# daemons.
#
# To disable synchronization (the default), do nothing.
#
# To enable synchronization, you must uncomment the following line:
#
# NOTE: Please read README.Fedora before enabling sync
#SYNC_SERVER = http://xmlrpc.denyhosts.net:9911
#
#######################################################################
#######################################################################
#
# SYNC_INTERVAL: the interval of time to perform synchronizations if
# SYNC_SERVER has been uncommented. The default is 1 hour.
#
#SYNC_INTERVAL = 1h
#
#######################################################################
#######################################################################
#
# SYNC_UPLOAD: allow your DenyHosts daemon to transmit hosts that have
# been denied? This option only applies if SYNC_SERVER has
# been uncommented.
# The default is SYNC_UPLOAD = yes
#
SYNC_UPLOAD = no
#SYNC_UPLOAD = yes
#
#######################################################################
#######################################################################
#
# SYNC_DOWNLOAD: allow your DenyHosts daemon to receive hosts that have
# been denied by others? This option only applies if SYNC_SERVER has
# been uncommented.
# The default is SYNC_DOWNLOAD = yes
#
SYNC_DOWNLOAD = no
#SYNC_DOWNLOAD = yes
#
#
#
#######################################################################
#######################################################################
#
# SYNC_DOWNLOAD_THRESHOLD: If SYNC_DOWNLOAD is enabled this parameter
# filters the returned hosts to those that have been blocked this many
# times by others. That is, if set to 1, then if a single DenyHosts
# server has denied an ip address then you will receive the denied host.
#
# See also SYNC_DOWNLOAD_RESILIENCY
#
#SYNC_DOWNLOAD_THRESHOLD = 10
#
# The default is SYNC_DOWNLOAD_THRESHOLD = 3
#
#SYNC_DOWNLOAD_THRESHOLD = 3
#
#######################################################################
#######################################################################
#
# SYNC_DOWNLOAD_RESILIENCY: If SYNC_DOWNLOAD is enabled then the
# value specified for this option limits the downloaded data
# to this resiliency period or greater.
#
# Resiliency is defined as the timespan between a hackers first known
# attack and its most recent attack. Example:
#
# If the centralized denyhosts.net server records an attack at 2 PM
# and then again at 5 PM, specifying a SYNC_DOWNLOAD_RESILIENCY = 4h
# will not download this ip address.
#
# However, if the attacker is recorded again at 6:15 PM then the
# ip address will be downloaded by your DenyHosts instance.
#
# This value is used in conjunction with the SYNC_DOWNLOAD_THRESHOLD
# and only hosts that satisfy both values will be downloaded.
# This value has no effect if SYNC_DOWNLOAD_THRESHOLD = 1
#
# The default is SYNC_DOWNLOAD_RESILIENCY = 5h (5 hours)
#
# Only obtain hackers that have been at it for 2 days or more:
#SYNC_DOWNLOAD_RESILIENCY = 2d
#
# Only obtain hackers that have been at it for 5 hours or more:
#SYNC_DOWNLOAD_RESILIENCY = 5h
#
#######################################################################