修复说明：OpenSSH 7.7及之前版本中存在安全漏洞
OpenSSH（OpenBSD Secure Shell）是OpenBSD计划组所维护的一套用于安全访问远程计算机的连接工具。该工具是SSH协议的开源实现，支持对所有的传输进行加密，可有效阻止窃听、连接劫持以及其他网络级的攻击。OpenSSH 7.7及之前版本中存在安全漏洞，该漏洞源于程序会对有效的和无效的身份验证请求发出不同的响应。攻击者可通过发送特制的请求利用该漏洞枚举用户名称。
1）安装telnet-server及xinetd
ll /etc/xinetd.d/telnet
cat /etc/securetty
echo '''pts/0
pts/1
pts/2
pts/3''' >> /etc/securetty
cat /etc/securetty
systemctl enable xinetd
systemctl enable telnet.socket
systemctl status telnet.socket
systemctl start telnet.socket
systemctl start xinetd
netstat -lntp|grep 23
systemctl status xinetd
systemctl restart telnet.socket
2）安装相关依赖包：
yum install -y gcc gcc-c++ glibc make autoconf openssl openssl-devel pcre-devel pam-devel
yum install -y pam* zlib*
3）安装openssl-1.0.2r 下载链接： https://openbsd.hk/pub/OpenBSD/OpenSSH/portable/
tar xfz openssl-1.0.2r.tar.gz
mv /usr/bin/openssl /usr/bin/openssl_bak
mv /usr/include/openssl /usr/include/openssl_bak
cd openssl-1.0.2r/
./config shared && make && make install
echo $?
ln -s /usr/local/ssl/bin/openssl /usr/bin/openssl
ln -s /usr/local/ssl/include/openssl /usr/include/openssl
echo "/usr/local/ssl/lib" >> /etc/ld.so.conf
/sbin/ldconfig
openssl version
4）安装openssh-8.0p1.tar.gz 下载链接：https://ftp.openssl.org/source/old/1.0.2/
tar -xzf openssh-8.0p1.tar.gz
cd openssh-8.0p1/
chown -R root.root ~/openssh-data/openssh-8.0p1
mv /usr/lib/systemd/system/sshd.service /app/
rm -rf /etc/ssh/*
./configure --prefix=/usr/ --sysconfdir=/etc/ssh --with-openssl-includes=/usr/local/ssl/include --with-ssl-dir=/usr/local/ssl --with-zlib --with-md5-passwords --with-pam && make && make install
cp -a contrib/redhat/sshd.init /etc/init.d/sshd
cp -a contrib/redhat/sshd.pam /etc/pam.d/sshd.pam
修改sshd服务配置：
vim /etc/ssh/sshd_config
chmod +x /etc/init.d/sshd
chkconfig --add sshd
systemctl enable sshd
systemctl status sshd
systemctl restart sshd
systemctl status sshd
systemctl stop sshd
systemctl status sshd
systemctl start sshd
systemctl status sshd
systemctl enable sshd
ssh -V
