public-health-ch/ansible/roles/dev-sec.ssh-hardening/templates/opensshd.conf.j2

# {{ansible_managed}}

# This is the ssh client system-wide configuration file.
# See sshd_config(5) for more information on any settings used. Comments will be added only to clarify why a configuration was chosen.

# Basic configuration
# ===================

# Either disable or only allowssh root login via certificates.
PermitRootLogin {{ 'without-password' if ssh_allow_root_with_key else 'no' }}

# Define which port sshd should listen to. Default to `22`.
{% for port in ssh_server_ports -%}
Port {{port}}
{% endfor %}

# Address family should always be limited to the active network configuration.
AddressFamily {{ 'any' if network_ipv6_enable else 'inet' }}

# Define which addresses sshd should listen to. Default to `0.0.0.0`, ie make sure you put your desired address in here, since otherwise sshd will listen to everyone.
{% for address in ssh_listen_to -%}
ListenAddress {{address}}
{% endfor %}

# List HostKeys here.
{% for key in ssh_host_key_files -%}
HostKey {{key}}          # Req 20
{% endfor %}

# Security configuration
# ======================

# Set the protocol version to 2 for security reasons. Disables legacy support.
Protocol 2

# Make sure sshd checks file modes and ownership before accepting logins. This prevents accidental misconfiguration.
StrictModes yes

# Logging, obsoletes QuietMode and FascistLogging
SyslogFacility AUTH
LogLevel VERBOSE

# Cryptography
# ------------

# **Ciphers** -- If your clients don't support CTR (eg older versions), cbc will be added
# CBC: is true if you want to connect with OpenSSL-base libraries
# eg ruby Net::SSH::Transport::CipherFactory requires cbc-versions of the given openssh ciphers to work
# -- see: (http://net-ssh.github.com/net-ssh/classes/Net/SSH/Transport/CipherFactory.html)
#
{% if ssh_server_cbc_required -%}
    {% if (ansible_distribution == 'Ubuntu' and ansible_distribution_version >= '14.04') or (ansible_distribution == 'Debian' and ansible_distribution_version >= '8') or (ansible_os_family in ['Oracle Linux', 'RedHat'] and ansible_distribution_major_version >= '7') or (ansible_distribution == 'FreeBSD' and ansible_distribution_version >= '11') -%}
        Ciphers {{ ssh_ciphers_66_weak | join(',') }}
    {% else %}
        Ciphers {{ ssh_ciphers_53_weak | join(',') }}
    {% endif %}
{% else -%}
    {% if (ansible_distribution == 'Ubuntu' and ansible_distribution_version >= '14.04') or (ansible_distribution == 'Debian' and ansible_distribution_version >= '8') or (ansible_os_family in ['Oracle Linux', 'RedHat'] and ansible_distribution_major_version >= '7') or (ansible_distribution == 'FreeBSD' and ansible_distribution_version >= '11') -%}
        Ciphers {{ ssh_ciphers_66_default | join(',') }}
    {% else -%}
        Ciphers {{ ssh_ciphers_53_default | join(',') }}
    {% endif %}
{% endif %}

# **Hash algorithms** -- Make sure not to use SHA1 for hashing, unless it is really necessary.
# Weak HMAC is sometimes required if older package versions are used
# eg Ruby's Net::SSH at around 2.2.* doesn't support sha2 for hmac, so this will have to be set true in this case.
#

{% if ssh_server_weak_hmac -%}
    {% if (ansible_distribution == 'Ubuntu' and ansible_distribution_version >= '14.04') or (ansible_distribution == 'Debian' and ansible_distribution_version >= '8') or (ansible_os_family in ['Oracle Linux', 'RedHat'] and ansible_distribution_major_version >= '7') or (ansible_distribution == 'FreeBSD' and ansible_distribution_version >= '11') -%}
        MACs {{ ssh_macs_66_weak | join(',') }}
    {% elif ansible_os_family in ['Oracle Linux', 'RedHat'] and ansible_distribution_major_version <= '6' -%}
        MACs {{ ssh_macs_53_default | join(',') }}
    {% endif %}
{% else -%}
    {% if (ansible_distribution == 'Ubuntu' and ansible_distribution_version >= '14.04') or (ansible_distribution == 'Debian' and ansible_distribution_version >= '8') or (ansible_os_family in ['Oracle Linux', 'RedHat'] and ansible_distribution_major_version >= '7') or (ansible_distribution == 'FreeBSD' and ansible_distribution_version >= '11') -%}
        MACs {{ ssh_macs_66_default | join(',') }}
    {% elif ansible_os_family in ['Oracle Linux', 'RedHat'] and ansible_distribution_major_version <= '6' -%}
        MACs {{ ssh_macs_53_default | join(',') }}
    {% else -%}
        MACs {{ ssh_macs_59_default | join(',') }}
    {% endif %}
{% endif %}

# Alternative setting, if OpenSSH version is below v5.9
#MACs hmac-ripemd160

# **Key Exchange Algorithms** -- Make sure not to use SHA1 for kex, unless it is really necessary
# Weak kex is sometimes required if older package versions are used
# eg ruby's Net::SSH at around 2.2.* doesn't support sha2 for kex, so this will have to be set true in this case.
# based on: https://bettercrypto.org/static/applied-crypto-hardening.pdf
{% if (ansible_distribution == 'Ubuntu' and ansible_distribution_version >= '14.04') or (ansible_distribution == 'Debian' and ansible_distribution_version >= '8') or (ansible_os_family in ['Oracle Linux', 'RedHat'] and ansible_distribution_major_version >= '7') or (ansible_distribution == 'FreeBSD' and ansible_distribution_version >= '11') -%}
    {% if ssh_server_weak_kex -%}
        KexAlgorithms {{ ssh_kex_66_weak | join(',') }}
    {% else -%}
        KexAlgorithms {{ ssh_kex_66_default | join(',') }}
    {% endif %}
{% else -%}
    {% if ansible_os_family in ['Oracle Linux', 'RedHat'] and ansible_distribution_major_version <= '6' -%}
        #KexAlgorithms
    {% elif ssh_server_weak_kex -%}
        KexAlgorithms {{ sshd_kex_59_weak | join(',') }}
    {% else -%}
        KexAlgorithms {{ ssh_kex_59_default | join(',') }}
    {% endif %}
{% endif %}

# Authentication
# --------------

# Secure Login directives.
UseLogin no
UsePrivilegeSeparation {% if (ansible_distribution == 'Debian' and ansible_distribution_major_version <= '6') or (ansible_os_family in ['Oracle Linux', 'RedHat'] and ansible_distribution_major_version <= '6') -%}{{ssh_ps53}}{% else %}{{ssh_ps59}}{% endif %}

PermitUserEnvironment no
LoginGraceTime 30s
MaxAuthTries {{ssh_max_auth_retries}}
MaxSessions 10
MaxStartups 10:30:100

# Enable public key authentication
PubkeyAuthentication yes

# Never use host-based authentication. It can be exploited.
IgnoreRhosts yes
IgnoreUserKnownHosts yes
HostbasedAuthentication no

# Enable PAM to enforce system wide rules
UsePAM {{ 'yes' if ssh_use_pam else 'no' }}

# Disable password-based authentication, it can allow for potentially easier brute-force attacks.
PasswordAuthentication no
PermitEmptyPasswords no
ChallengeResponseAuthentication {{ 'yes' if ssh_challengeresponseauthentication else 'no' }}

# Only enable Kerberos authentication if it is configured.
KerberosAuthentication no
KerberosOrLocalPasswd no
KerberosTicketCleanup yes
#KerberosGetAFSToken no

# Only enable GSSAPI authentication if it is configured.
GSSAPIAuthentication no
GSSAPICleanupCredentials yes

# In case you don't use PAM (`UsePAM no`), you can alternatively restrict users and groups here. For key-based authentication this is not necessary, since all keys must be explicitely enabled.
{% if ssh_deny_users -%}
DenyUsers {{ssh_deny_users}}
{% endif %}

{% if ssh_allow_users -%}
AllowUsers {{ssh_allow_users}}
{% endif %}

{% if ssh_deny_groups -%}
DenyGroups {{ssh_deny_groups}}
{% endif %}

{% if ssh_allow_groups -%}
AllowGroups {{ssh_allow_groups}}
{% endif %}

# Network
# -------

# Disable TCP keep alive since it is spoofable. Use ClientAlive messages instead, they use the encrypted channel
TCPKeepAlive no

# Manage `ClientAlive..` signals via interval and maximum count. This will periodically check up to a `..CountMax` number of times within `..Interval` timeframe, and abort the connection once these fail.
ClientAliveInterval {{ssh_client_alive_interval}}
ClientAliveCountMax {{ssh_client_alive_count}}

# Disable tunneling
PermitTunnel no

# Disable forwarding tcp connections.
# no real advantage without denied shell access
AllowTcpForwarding {{ 'yes' if ssh_allow_tcp_forwarding else 'no' }}

# Disable agent formwarding, since local agent could be accessed through forwarded connection.
# no real advantage without denied shell access
AllowAgentForwarding {{ 'yes' if ssh_allow_agent_forwarding else 'no' }}

# Do not allow remote port forwardings to bind to non-loopback addresses.
GatewayPorts no

# Disable X11 forwarding, since local X11 display could be accessed through forwarded connection.
X11Forwarding no
X11UseLocalhost yes


# Misc. configuration
# ===================

PrintMotd {{ 'yes' if ssh_print_motd else 'no' }}

{% if ansible_os_family != 'FreeBSD' %}
PrintLastLog {{ 'yes' if ssh_print_last_log else 'no' }}
{% endif %}

Banner {{ '/etc/ssh/banner.txt' if ssh_banner else 'none' }}

{% if ansible_os_family == 'Debian' %}
DebianBanner {{ 'yes' if ssh_print_debian_banner else 'no' }}
{% endif %}

{% if sftp_enabled %}
# Configuration, in case SFTP is used
## override default of no subsystems
## Subsystem sftp /opt/app/openssh5/libexec/sftp-server
Subsystem sftp internal-sftp -l INFO -f LOCAL6
#
## These lines must appear at the *end* of sshd_config
Match Group sftponly
ForceCommand internal-sftp -l INFO -f LOCAL6
ChrootDirectory {{ sftp_chroot_dir }}
AllowTcpForwarding no
AllowAgentForwarding no
PasswordAuthentication no
PermitRootLogin no
X11Forwarding no
{% endif %}