Linux基础服务sshd简介

亦凉 2022-09-10 13:29 248阅读 0赞

# sshd由OpenSSH来提供 #

*  SSH 协议：Secure Shell，安全的shell协议。
 *  SSH 为建立在应用层和传输层基础上的安全协议。
 *  sshd服务使用SSH协议可以用来进行远程控制， 或在计算机之间传送文件。
 *  sshd使用加密传输，较之使用明文传输的telnet传输文件要安全很多。

## sshd配置文件 ##

`/etc/ssh/sshd_config`

*  如果井号开头的和后面参数没有空格的，表示默认值,是生效的
 *  如果井号开头和后面有空格的，表示纯注释

## 调优参数 ##

### 端口 ###

*  默认端口22，外网生产环境需要修改  
    `Port 22`
 *  使用参数指定端口连接非22默认端口\[-p port\]  
    `ssh -p 1234 root@10.0.0.88`

### 监听地址 ###

*  默认缺省值为所有网卡的所有地址
 *  可以修改为指定IP

#ListenAddress 0.0.0.0
    #ListenAddress ::

### 登陆等待时间 ###

*  从输入用户名到敲入密码的登陆等待时间
 *  默认是2分钟，可以调的小一些  
    `#LoginGraceTime 2m`

### 允许root登录 ###

*  生产环境应该禁止root直接登录
 *  Debian系列例如Ubuntu是默认禁止root登陆的  
    `PermitRootLogin yes`

### 默认认证公钥文件 ###

`AuthorizedKeysFile .ssh/authorized_keys`

### 是否允许使用密码认证登录 ###

*  做过密钥认证以后可关闭密码认证登录，防止暴力破解  
    `PasswordAuthentication yes`

### 打印登陆提示信息和最后登录日志 ###

*  发现被黑线索  
    `PrintMotd no`  
    `#PrintLastLog yes`

[14:56:49 root@C8-88[ ~]#ssh 10.0.0.189
    Last login: Sat Jul  3 22:00:12 2021 from 10.0.0.88

### 使用DNS反向解析 ###

*  如果敲完密码一直卡着，半天才进系统，可以将此项改为no  
    `#UseDNS no`

## 修改登录提示 ##

*  创建或修改motd文件  
    `/etc/motd`
 *  在文件中添加需要登录显示的内容
 *  修改配置文件打开PrintMotd  
    `sed -ri.bak 's/(PrintMotd )no/\1yes/' /etc/ssh/sshd_config`

## fail2ban防止暴力破解 ##

*  监控日志系统，匹配日志信息，将过分的ip加入到ipatble中
 *  python写的用python装py包
 *  主配置文件jail.conf
 *  模板服务文件在源码包的files中，fail2ban.service,redhat-initd
 *  查找古时候的启动文件,文件内容带有chkconfig相关字样  
    `grep chkconfig ./* -R --color`
 *  老版本使用chkconfig添加启动项  
    `chekconfig --add fail2ban`
 *  登录日志

### 相关主要文件说明： ###

*  jail \[dʒeɪl\]监狱

/etc/fail2ban/action.d #动作文件夹，内含默认文件。iptables以及mail等动作配置
    /etc/fail2ban/fail2ban.conf    #定义了fai2ban日志级别、日志位置及sock文件位置
    /etc/fail2ban/filter.d                     #条件文件夹，内含默认文件。过滤日志关键内容设置
    /etc/fail2ban/jail.conf     #主要配置文件，模块化。主要设置启用ban动作的服务及动作阀值

## 应用案例 ##

*  远程ssh用户5分钟三次失败则禁用1小时
 *  防止频繁试密码
 *  修改\[ssh-iptables\]
 *  先启用功能  
    `enabled = ture`
 *  指定日志  
    `logpath = /var/log/secure`
 *  发一批邮件改sentmail，系统中需要已启用sentmail
 *  如果ssh服务器不是22端口，则需要改配置文件，
 *  iptables配置文件也要改

## 查看ban的状态 ##

`fail2ban-client status ssh-iptable`

## 使用shell脚本实现fail2ban功能 ##

*  利用定时任务查看安全日志
 *  将超过阈值的IP加入系统黑名单hosts.deny中去

#!/bin/bash
    cat var/log/secure | awk '/Failed/{print $(NF-3)}' | sort | uniq -c | awk '{print $2"="$1;}' > /root/satools/black.txt
    DEFINE='10'
    for i in `cat /root/satools/black.txt`;do
        IP=`echo $i | awk -F= '{print $1}'`
        NUM=`echo $i | awk -F= '{print $2}'`
    
        if [ $NUM -gt $DEFINE ];then
            grep $IP /etc/hosts.deny > /dev/null
            if [ $? -gt 0 ];then
                echo "sshd:$IP" >> /etc/hosts/deny
            fi
        fi
    done

## 利用denyhosts实现 ##

*  epel中的denyhosts简单实现

## 系统再带pam模块提供防护功能 ##

*  系统本身体统pam模块功能  
    `/etc/pam.d/sshd`
 *  添加错误尝试次数，和锁定时间
 *  在第一行下面添加一条规则  
    `auth required pam_tally2.so deny=3 unlock_time=600 even_deny_root root_unlock_time=1200`

### pam模块命令 ###

*  查看用户登录次数  
    手动解除锁定：  
    查看某一用户错误登陆次数：  
    pam\_tally –-user  
    例如，查看work用户的错误登陆次数：  
    pam\_tally –-user work  
    清空某一用户错误登陆次数：  
    pam\_tally –-user –-reset  
    例如，清空 work 用户的错误登陆次数，  
    pam\_tally –-user work –-reset

## xshell等客户端免密登录服务器 ##

*  使用xshell等客户端本地生成公钥文件
 *  将生成的公钥文件放到服务器对应的用户家目录的.ssh目录中去

==========================================================  
配置文件内容：

# $OpenBSD: sshd_config,v 1.103 2018/04/09 20:41:22 tj Exp $
    
    # This is the sshd server system-wide configuration file. See
    # sshd_config(5) for more information.
    
    # This sshd was compiled with PATH=/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin
    
    # The strategy used for options in the default sshd_config shipped with
    # OpenSSH is to specify options with their default value where
    # possible, but leave them commented. Uncommented options override the
    # default value.
    
    # If you want to change the port on a SELinux system, you have to tell
    # SELinux about this change.
    # semanage port -a -t ssh_port_t -p tcp #PORTNUMBER
    #
    #Port 22
    #AddressFamily any
    #ListenAddress 0.0.0.0
    #ListenAddress ::
    
    HostKey /etc/ssh/ssh_host_rsa_key
    HostKey /etc/ssh/ssh_host_ecdsa_key
    HostKey /etc/ssh/ssh_host_ed25519_key
    
    # Ciphers and keying
    #RekeyLimit default none
    
    # System-wide Crypto policy:
    # This system is following system-wide crypto policy. The changes to
    # Ciphers, MACs, KexAlgoritms and GSSAPIKexAlgorithsm will not have any
    # effect here. They will be overridden by command-line options passed on
    # the server start up.
    # To opt out, uncomment a line with redefinition of CRYPTO_POLICY=
    # variable in /etc/sysconfig/sshd to overwrite the policy.
    # For more information, see manual page for update-crypto-policies(8).
    
    # Logging
    #SyslogFacility AUTH
    SyslogFacility AUTHPRIV
    #LogLevel INFO
    
    # Authentication:
    
    #LoginGraceTime 2m
    PermitRootLogin yes
    #StrictModes yes
    #MaxAuthTries 6
    #MaxSessions 10
    
    #PubkeyAuthentication yes
    
    # The default is to check both .ssh/authorized_keys and .ssh/authorized_keys2
    # but this is overridden so installations will only check .ssh/authorized_keys
    AuthorizedKeysFile	.ssh/authorized_keys
    
    #AuthorizedPrincipalsFile none
    
    #AuthorizedKeysCommand none
    #AuthorizedKeysCommandUser nobody
    
    # For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
    #HostbasedAuthentication no
    # Change to yes if you don't trust ~/.ssh/known_hosts for
    # HostbasedAuthentication
    #IgnoreUserKnownHosts no
    # Don't read the user's ~/.rhosts and ~/.shosts files
    #IgnoreRhosts yes
    
    # To disable tunneled clear text passwords, change to no here!
    #PasswordAuthentication yes
    #PermitEmptyPasswords no
    PasswordAuthentication yes
    
    # Change to no to disable s/key passwords
    #ChallengeResponseAuthentication yes
    ChallengeResponseAuthentication no
    
    # Kerberos options
    #KerberosAuthentication no
    #KerberosOrLocalPasswd yes
    #KerberosTicketCleanup yes
    #KerberosGetAFSToken no
    #KerberosUseKuserok yes
    
    # GSSAPI options
    GSSAPIAuthentication yes
    GSSAPICleanupCredentials no
    #GSSAPIStrictAcceptorCheck yes
    #GSSAPIKeyExchange no
    #GSSAPIEnablek5users no
    
    # Set this to 'yes' to enable PAM authentication, account processing,
    # and session processing. If this is enabled, PAM authentication will
    # be allowed through the ChallengeResponseAuthentication and
    # PasswordAuthentication. Depending on your PAM configuration,
    # PAM authentication via ChallengeResponseAuthentication may bypass
    # the setting of "PermitRootLogin without-password".
    # If you just want the PAM account and session checks to run without
    # PAM authentication, then enable this but set PasswordAuthentication
    # and ChallengeResponseAuthentication to 'no'.
    # WARNING: 'UsePAM no' is not supported in Fedora and may cause several
    # problems.
    UsePAM yes
    
    #AllowAgentForwarding yes
    #AllowTcpForwarding yes
    #GatewayPorts no
    X11Forwarding yes
    #X11DisplayOffset 10
    #X11UseLocalhost yes
    #PermitTTY yes
    
    # It is recommended to use pam_motd in /etc/pam.d/sshd instead of PrintMotd,
    # as it is more configurable and versatile than the built-in version.
    PrintMotd no
    
    #PrintLastLog yes
    #TCPKeepAlive yes
    #PermitUserEnvironment no
    #Compression delayed
    #ClientAliveInterval 0
    #ClientAliveCountMax 3
    #UseDNS no
    #PidFile /var/run/sshd.pid
    #MaxStartups 10:30:100
    #PermitTunnel no
    #ChrootDirectory none
    #VersionAddendum none
    
    # no default banner path
    #Banner none
    
    # Accept locale-related environment variables
    AcceptEnv LANG LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE LC_MONETARY LC_MESSAGES
    AcceptEnv LC_PAPER LC_NAME LC_ADDRESS LC_TELEPHONE LC_MEASUREMENT
    AcceptEnv LC_IDENTIFICATION LC_ALL LANGUAGE
    AcceptEnv XMODIFIERS
    
    # override default of no subsystems
    Subsystem	sftp	/usr/libexec/openssh/sftp-server
    
    # Example of overriding settings on a per-user basis
    #Match User anoncvs
    # X11Forwarding no
    # AllowTcpForwarding no
    # PermitTTY no
    # ForceCommand cvs server