Usage

Usage

OpenSSH is a free version of the SSH connectivity tools that technical users of the Internet rely on. The passwords of Telnet, remote login (rlogin), and File Transfer Protocol (FTP) users are transmitted across the Internet unencrypted. OpenSSH encrypts all traffic, including passwords, to effectively eliminate eavesdropping, connection hijacking, and other attacks. Additionally, OpenSSH provides secure tunneling capabilities and several authentication methods, and supports all SSH protocol versions.

This file provides the sample pillars configurations for different use cases.

OpenSSH client

  • The OpenSSH client configuration with a shared private key:

    openssh:
      client:
        enabled: true
        use_dns: False
        user:
          root:
            enabled: true
            private_key:
              type: rsa
              key: ${_param:root_private_key}
            user: ${linux:system:user:root}
    
  • The OpenSSH client configuration with an individual private key and known host:

    openssh:
      client:
        enabled: true
        user:
          root:
            enabled: true
            user: ${linux:system:user:root}
            known_hosts:
            - name: repo.domain.com
              type: rsa
              fingerprint: dd:fa:e8:68:b1:ea:ea:a0:63:f1:5a:55:48:e1:7e:37
              fingerprint_hash_type: sha256|md5
    
  • The OpenSSH client configuration with keep alive settings:

    openssh:
      client:
        alive:
          interval: 600
          count: 3
    

OpenSSH server

  • The OpenSSH server simple configuration:

    openssh:
      server:
        enabled: true
        permit_root_login: true
        public_key_auth: true
        password_auth: true
        host_auth: true
        banner: Welcome to server!
        bind:
          address: 0.0.0.0
          port: 22
    
  • The OpenSSH server configuration with auth keys for users:

    openssh:
      server:
        enabled: true
        bind:
          address: 0.0.0.0
          port: 22
        ...
        user:
          newt:
            enabled: true
            user: ${linux:system:user:newt}
            public_keys:
            - ${public_keys:newt}
          root:
            enabled: true
            purge: true
            user: ${linux:system:user:root}
            public_keys:
            - ${public_keys:newt}
    

    Note

    Setting the purge parameter to true ensures that the exact authorized_keys contents will be filled explicitly from the model and undefined keys will be removed.

  • The OpenSSH server configuration that binds OpenSSH on multiple addresses and ports:

    openssh:
      server:
        enabled: true
        binds:
          - address: 127.0.0.1
            port: 22
          - address: 192.168.1.1
            port: 2222
    
  • The OpenSSH server with FreeIPA configuration:

    openssh:
      server:
        enabled: true
        bind:
          address: 0.0.0.0
          port: 22
        public_key_auth: true
        authorized_keys_command:
          command: /usr/bin/sss_ssh_authorizedkeys
          user: nobody
    
  • The OpenSSH server configuration with keep alive settings:

    openssh:
      server:
        alive:
          keep: yes
          interval: 600
          count: 3
    #
    # will give you an timeout of 30 minutes (600 sec x 3)
    
  • The OpenSSH server configuration with the DSA legacy keys enabled:

    openssh:
      server:
        dss_enabled: true
    
  • The OpenSSH server configuration with the duo 2FA https://duo.com/docs/duounix with Match User 2FA can be bypassed for some accounts

    openssh:
      server:
        use_dns: false
        password_auth: false
        challenge_response_auth: true
        ciphers:
          aes256-ctr:
            enabled: true
          aes192-ctr:
            enabled: true
          aes128-ctr:
            enabled: true
        authentication_methods:
          publickey:
            enabled: true
          keyboard-interactive:
            enabled: true
        match_user:
          jenkins:
            authentication_methods:
              publickey:
                enabled: true
    
  • OpenSSH server configuration supports AllowUsers, DenyUsers, AllowGroup, DenyGroups via allow_users, deny_users, allow_groups, deny_groups keys respectively.

    For example, here is how to manage AllowUsers configuration item:

    openssh:
      server:
        allow_users:
          <user_name>:
            enabled: true
          <pattern_list_name>:
            enabled: true
            pattern: <pattern>
    

Elements of allow_users are either user names or pattern list names:

  • <user name> goes to configurational file as is.

  • <pattern list name> is not used directly - its main purpose is to provide a meaningfull name for a pattern specified in ‘pattern’ key. Another advantage is that pattern can be overriden.

<enabled> by default is ‘true’.

See PATTERNS in ssh_config(5) for more information on what <pattern> is.

CIS Compliance

There is a number of configuration options that make the OpenSSH service compliant with CIS Benchmark. These options can be found under metadata/service/server/cis, and are not enabled by default. For each CIS item a comprehensive description is provided with the pillar data.

See also https://www.cisecurity.org/cis-benchmarks/ for the details abouth CIS Benchmark.

Read more