Using CheatSheets To Apply Best Practices

SSH Cheatsheet

SSH Cheatsheet


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1.1 SSH general

Name Summary
Install ssh server apt-get install openssh
Run ssh command ssh -o StrictHostKeyChecking=no -p 2702 root@172.17.0.8 date
SSH with verbose ouptut ssh -vvv -p 2702 root@45.33.87.74 date 2>&1
ssh without input password sshpass -p '<your-passwd>' ssh <username>@<ssh_host>, brew install sshpass
SSH passwordless login ssh-copy-id <username>@<ssh_host>, Or manually update ~/.ssh/authorized_keys
Remove an entry from known_hosts file ssh-keygen -f ~/.ssh/known_hosts -R github.com
Diff local file with remote one diff local_file.txt <(ssh <username>@<ssh_host> 'cat remote_file.txt')
Diff two remote ssh files diff <(ssh user@remote_host 'cat file1.txt') <(ssh user2@remote_host2 'cat file2.txt')
Upload with timestamps/permissions kept scp -rp /tmp/abc/ ec2-user@<ssh-host>:/root/
SSH agent load key exec ssh-agent bash && ssh-keygen, ssh-add
Emacs read remote file with tramp emacs /ssh:<username>@<ssh_host>:/path/to/file

1.2 SSH tools

Name Summary  
Export local env to Internet ngrok.com  
Reverse ssh proxy sshuttle  
SSH by auto input password sshpass sshpass -p “$PASSWORD” ssh -o StrictHostKeyChecking=no $username@$sship=  

1.3 SCP

Name Summary
Download a remote folder scp -r ec2-user@<ssh-host>:/home/letsencrypt-20180825 ./
Upload a file scp -i <ssh-keyfile> /tmp/hosts ec2-user@<ssh-host>:/root/
Upload a folder scp -r /tmp/abc/ ec2-user@<ssh-host>:/root/
Upload with timestamps/permissions kept scp -rp /tmp/abc/ ec2-user@<ssh-host>:/root/
Mount remote directory as local folder sshfs name@server:/path/remote_folder /path/local_folder

1.4 SSH security

Name Summary
Disable ssh by password sed -i 's/PasswordAuthentication yes/PasswordAuthentication no/g' /etc/ssh/sshd_config
Disable root login sed -i 's/^PermitRootLogin yes/#PermitRootLogin yes/' /etc/ssh/sshd_config
Enable/Disable SSH Host Key Checking StrictHostKeyChecking yes change ~/.ssh/config
Protect SSH server from brute force attacks fail2ban command line tool

1.5 SSH tunnel

Name Summary
SSH port forward to a local port ssh -N -i <ssh-keyfile> -f root@54.179.178.214 -L *:18085:localhost:8085 -n /bin/bash
Reverse port forward to remote server ssh -R *:40099:localhost:22 root@54.179.178.214, ssh -p 40099 root@54.179.178.214

1.6 SSH files

Name Summary
Generate a new key pair ssh-keygen, ssh-keygen -C "your_email@example.com" -t rsa
Generate key pair without interaction ssh-keygen -t rsa -f /tmp/sshkey -N "" -q
Add passphrase protection to ssh keyfile ssh-keygen -p -f id_rsa Link: Manage SSH Key File With Passphrase
Convert OpenSSL format to SSH-RSA format ssh-keygen -f my_ssh.pub -i
Critical ssh files/folders ~/.ssh/authorized_keys, ~/.ssh/config, ~/.ssh/known_hosts
SSH config file /etc/ssh/ssh_config, /etc/ssh/sshd_config
SSH key file permission chmod 600 ~/.ssh/id_rsa
SSH folder permission chmod 700 ~/.ssh, chown -R $USER:$USER ~/.ssh
Authorizedkeys file permission chmod 644 ~/.ssh/authorized_keys

1.7 Parse ssh log file

Name Command
Events of ssh down grep -R "ssh.*Received signal 15" /var/log/auth.log
Events of ssh up grep -R "sshd.*Server listening" /var/log/auth.log
Events of ssh failed login grep -R "sshd.*Failed password for invalid user" /var/log/auth.log
Events of ssh break-in attemp grep -R "sshd.*POSSIBLE BREAK-IN ATTEMPT!" /var/log/auth.log
Events of ssh port scap grep -R "sshd.*Bad protocol version identification" /var/log/auth.log
Events of ssh login by public key grep -R "sshd.*Accepted publickey for" /var/log/auth.log
Events of ssh login by password grep -R "sshd.*Accepted password for" /var/log/auth.log
Events of ssh logout event grep -R "sshd.*pam_unix(sshd:session): session closed for" /var/log/auth.log

1.8 Scripts

  • Inject local key to remote ssh server server
cat ~/.ssh/id_rsa.pub | ssh $username@$ssh_hostk "cat - >> ~/.ssh/authorized_keys"

ssh $username@$ssh_hostk "cat ~/.ssh/authorized_keys"

  • SSH Config file
Host sandbox
     HostName 192.168.50.10
     StrictHostKeyChecking no
     User root
Host 192.168.1.*
   StrictHostKeyChecking no
   Port 32882
   UserKnownHostsFile=/dev/null
   IdentityFile ~/.ssh/id_rsa
  • Use expect to run ssh command with credential auto input
#!/usr/bin/expect
set timeout 20
set command "cat /etc/hosts"
set user "vagrant"
set password "vagrant"
set ip "192.168.50.10"
spawn ssh -o stricthostkeychecking=no $user@$ip "$command"
expect "*password:*"
send "$password\r"
expect eof;
  • ssh reverse tunnel
# https://www.howtoforge.com/reverse-ssh-tunneling

autossh -M 40000 -p 2702 -i /home/denny/al -fN \
    -o "PubkeyAuthentication=yes" \
    -o "StrictHostKeyChecking=false" -o "PasswordAuthentication=no" \
    -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" \
    -R 123.57.240.189:29995:localhost:22 root@123.57.240.189


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