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Nguyen Trung Duc
Nguyen Trung Duc

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Hardening ssh service on Ubuntu/Linux server

#devops #linux #ubuntu

Checklist:

  • Disable ssh login for root user
  • Disable password login

1. Create new user 

adduser <username>
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Add user to sudo group:

usermod -aG sudo <username>
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or add this line to file /etc/sudoers.d/90-cloud-init-users (sudo without password)

<username> ALL=(ALL) NOPASSWD:ALL
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2. Add ssh key for new user

Add ssh key to file /home/<username>/.ssh/authorized_keys

3. Disable root login and password based login

Edit file /etc/ssh/sshd_config, Find ChallengeResponseAuthentication and set to no:

ChallengeResponseAuthentication no
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find PasswordAuthentication set to no:

PasswordAuthentication no
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Search for UsePAM and set to no:

UsePAM no
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Finally look for PermitRootLogin and set it to no:

PermitRootLogin no
PermitRootLogin prohibit-password
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Save and close the file. Reload or restart the ssh server on Linux:

service ssh restart
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