问题描述：OpenSSH 用户枚举漏洞(CVE-2018-15473)【原理扫描】
OpenSSH do_setup_env函数权限提升漏洞(CVE-2015-8325)
OpenSSH auth_password函数拒绝服务漏洞(CVE-2016-6515)
OpenSSH多个拒绝服务漏洞（CVE-2016-10708）
OpenSSH 安全限制绕过漏洞(CVE-2016-10012)
OpenSSH 远程代码执行漏洞(CVE-2016-10009)
OpenSSH 安全漏洞(CVE-2016-1908)
解决方案：OpenSSH升级版本到最新(8.7)版本
具体操作：
1、依赖软件包：
yum install wget gcc -y
yum install -y zlib-devel openssl-devel
yum install pam-devel libselinux-devel zlib-devel openssl-devel -y
2、下载安装包OpenSSH8.7上传至服务器或wget直接下载
wget https://cdn.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-8.7p1.tar.gz
3、删除低版本OpenSSH的的rpm包
rpm -e --nodeps `rpm -qa | grep openssh`
4、安装openssh
解压
tar -zxvf openssh-8.7p1.tar.gz
cd openssh-8.7p1
./configure --prefix=/usr --sysconfdir=/etc/ssh --with-md5-passwords --with-pam --with-zlib --with-tcp-wrappers --with-ssl-dir=/usr/local/ssl --without-hardening
编译安装
Make
make install
赋权
chmod 600 /etc/ssh/ssh_host_rsa_key /etc/ssh/ssh_host_ecdsa_key /etc/ssh/ssh_host_ed25519_key
复制配置文件并设置允许root用户远程登录
cp -a contrib/redhat/sshd.init /etc/init.d/sshd
cp -a contrib/redhat/sshd.pam /etc/pam.d/sshd.pam
chmod u+x /etc/init.d/sshd
vim /etc/ssh/sshd_config
1.修改#PermitRootLogin prohibit-password项，去掉注释#并把prohibit-password改为yes，修改后即为PermitRootLogin yes
2.去掉注释#PasswordAuthentication yes变为PasswordAuthentication yes
添加添加自启服务ssh到开机启动项
chkconfig --add sshdchkconfig sshd on
重启服务
systemctl restart sshd
查看下安装结果：
ssh -V
注意：高版本升级会导致xshell或者xftp登陆报错
第一步检查/etc/ssh/sshd_config文件中配置
PermitRootLogin yes
PubkeyAuthentication yes
PasswordAuthentication yes
第二步检查是否开启防火墙
setenforce 0
第三步检查/etc/pam.d/sshd文件是否存在
/etc/pam.d/sshd文件必须存在，不存在就无法通过验证
centos7下的/etc/pam.d/sshd文件内容：
#%PAM-1.0
auth required pam_sepermit.so
auth substack password-auth
auth include postlogin
# Used with polkit to reauthorize users in remote sessions
-auth optional pam_reauthorize.so prepare
account required pam_nologin.so
account include password-auth
password include password-auth
# pam_selinux.so close should be the first session rule
session required pam_selinux.so close
session required pam_loginuid.so
# pam_selinux.so open should only be followed by sessions to be executed in the user context
session required pam_selinux.so open env_params
session required pam_namespace.so
session optional pam_keyinit.so force revoke
session include password-auth
session include postlogin
# Used with polkit to reauthorize users in remote sessions
-session optional pam_reauthorize.so prepare
（再重启sshd服务systemctl restart sshd）