Ansible Role for Server Hardening

This is an Ansible role designed to enhance the security of servers running on AlmaLinux, Debian, or Ubuntu.

It's systemd focused and requires Ansible version 2.15 or higher.

The role supports the following operating systems:

• AlmaLinux 9
• Debian 11 (Bullseye)
• Debian 12 (Bookworm)
• Ubuntu 22.04 (Jammy Jellyfish)
• Ubuntu 24.04 (Noble Numbat)

For those using AWS or Azure, there are also hardened Ubuntu Amazon Machine Images (AMIs) and Azure virtual machine images available.

These are available in the konstruktoid/hardened-images repository. These images are built using Packer and this Ansible role is used for configuration.

Note Do not use this role without first testing in a non-operational environment.

Note There is a SLSA artifact present under the slsa action workflow for verification.

Dependencies

None.

Examples

Requirements

---
roles:
  - name: konstruktoid.hardening
    version: v2.2.0
    src: https://github.com/konstruktoid/ansible-role-hardening.git
    scm: git

Playbook

---
- name: Import and use the hardening role
  hosts: localhost
  any_errors_fatal: true
  tasks:
    - name: Import the hardening role
      ansible.builtin.import_role:
        name: konstruktoid.hardening
      vars:
        sshd_admin_net:
          - 10.0.2.0/24
          - 192.168.0.0/24
          - 192.168.1.0/24
        suid_sgid_permissions: false

Local playbook using git checkout

---
- name: Checkout and configure konstruktoid.hardening
  hosts: localhost
  any_errors_fatal: true
  tasks:
    - name: Clone hardening repository
      become: true
      tags:
        - always
      block:
        - name: Install git
          ansible.builtin.package:
            name: git
            state: present

        - name: Checkout konstruktoid.hardening
          become: true
          ansible.builtin.git:
            repo: https://github.com/konstruktoid/ansible-role-hardening
            dest: /etc/ansible/roles/konstruktoid.hardening
            version: v2.2.0

        - name: Remove git
          ansible.builtin.package:
            name: git
            state: absent

    - name: Include the hardening role
      ansible.builtin.include_role:
        name: konstruktoid.hardening
      vars:
        sshd_allow_groups:
          - ubuntu
        sshd_login_grace_time: 60
        sshd_max_auth_tries: 10
        sshd_use_dns: false
        sshd_update_moduli: true

Note regarding UFW firewall rules

Instead of resetting ufw every run and by doing so causing network traffic disruption, the role deletes every ufw rule without comment: ansible managed task parameter and value.

The role also sets default deny policies, which means that firewall rules needs to be created for any additional ports except those specified in the sshd_ports and ufw_outgoing_traffic variables.

See ufw(8) for more information.

Task Execution and Structure

See STRUCTURE.md for tree of the role structure.

Role testing

See TESTING.md.

Role Variables with defaults

./defaults/main/aide.yml

manage_aide: true

aide_checksums: sha512
aide_dir_exclusions:
  - /var/lib/docker
  - /var/lib/lxcfs
  - /var/lib/private/systemd
  - /var/log/audit
  - /var/log/journal

If manage_aide: true, then AIDE will be installed and configured.

aide_checksums modifies the AIDE Checksums variable. Note that the Checksums variable might not be present depending on distribution.

aide_dir_exclusions is a list of directories that will be excluded from the AIDE database.

aide.conf(5)

./defaults/main/auditd.yml

manage_auditd: true

auditd_apply_audit_rules: true
auditd_action_mail_acct: root
auditd_admin_space_left_action: suspend
auditd_disk_error_action: suspend
auditd_disk_full_action: suspend
auditd_enable_flag: 2
auditd_flush: incremental_async
auditd_max_log_file: 20
auditd_max_log_file_action: rotate
auditd_mode: 1
auditd_num_logs: 5
auditd_space_left: 75
auditd_space_left_action: email
grub_audit_backlog_cmdline: audit_backlog_limit=8192
grub_audit_cmdline: audit=1

If manage_auditd: true, then the Linux Audit System will configured and enabled at boot using GRUB.

When auditd_apply_audit_rules: 'yes', the role applies the auditd rules from the included template file.

auditd_action_mail_acct should be a valid email address or alias.

auditd_admin_space_left_action defines what action to take when the system has detected that it is low on disk space. suspend will cause the audit daemon to stop writing records to the disk.

auditd_enable_flag sets the enabled flag. If 0 is passed, temporarily disable auditing. 1 will enable auditing and 2 will lock the audit configuration.

auditd_flush: sync tells the audit daemon to keep both the data and meta-data fully sync'd with every write to disk.

auditd_max_log_file_action sets what action to take when the system has detected that the max file size limit has been reached. E.g. the rotate option will cause the audit daemon to rotate the logs. The keep_logs option is similar to rotate except it does not use the num_logs setting. This prevents audit logs from being overwritten.

auditd_space_left_action tells the system what action to take when the system has detected that it is low on disk space. email means that it will send a warning to the email account specified in action_mail_acct as well as sending the message to syslog.

auditd_mode sets auditd failure mode, 0=silent 1=printk 2=panic.

auditd.conf(5)

./defaults/main/automatic_updates.yml

automatic_updates:
  enabled: true
  only_security: true
  reboot: false
  reboot_from_time: "2:00"
  reboot_time_margin_mins: 20

If automatic_updates is enabled it will install and configure dnf-automatic or unattended-upgrades, depending on the distribution.

If the reboot option is set to true, it will reboot the system if needed, see Unattended-Upgrade::Automatic-Reboot and dnf_automatic: reboot.

The reboot time scheduling is currently only supported on Debian-based distros. The reboot is by default scheduled randomly betweem 2:00-2:20AM, server time. The reboot time is chosen randomly from reboot_from_time, adding a random time within reboot_time_margin_mins to avoid overloading hypervisors.

./defaults/main/compilers.yml

manage_compilers: true

compilers:
  - as
  - cargo
  - cc
  - cc-[0-9]*
  - clang-[0-9]*
  - gcc
  - gcc-[0-9]*
  - go
  - make
  - rustc

If manage_compilers: true, then the listed compilers will be restricted to the root user.

./defaults/main/crypto_policies.yml

set_crypto_policy: true
crypto_policy: DEFAULT:NO-SHA1

Set and use cryptographic policies if /etc/crypto-policies/config exists and set_crypto_policy: true.

./defaults/main/disablewireless.yml

disable_wireless: false

If true, turn off all wireless interfaces.

./defaults/main/dns.yml

manage_resolved: true

dns:
  - 1.1.1.2
  - 9.9.9.9
fallback_dns:
  - 1.0.0.2
  - 149.112.112.112
dnssec: allow-downgrade
dns_over_tls: opportunistic

If manage_resolved: true, configure systemd-resolved.

IPv4 and IPv6 addresses to use as system and fallback DNS servers. If dnssec is set to "allow-downgrade" DNSSEC validation is attempted, but if the server does not support DNSSEC properly, DNSSEC mode is automatically disabled.

If dns_over_tls is true, all connections to the server will be encrypted if the DNS server supports DNS-over-TLS and has a valid certificate.

./defaults/main/ipv6.yml

disable_ipv6: false
sysctl_net_ipv6_conf_accept_ra_rtr_pref: 0

ipv6_disable_sysctl_settings:
  net.ipv6.conf.all.disable_ipv6: 1
  net.ipv6.conf.default.disable_ipv6: 1

ipv6_sysctl_settings:
  net.ipv6.conf.all.accept_ra: 0
  net.ipv6.conf.all.accept_redirects: 0
  net.ipv6.conf.all.accept_source_route: 0
  net.ipv6.conf.all.forwarding: 0
  net.ipv6.conf.all.use_tempaddr: 2
  net.ipv6.conf.default.accept_ra: 0
  net.ipv6.conf.default.accept_ra_defrtr: 0
  net.ipv6.conf.default.accept_ra_pinfo: 0
  net.ipv6.conf.default.accept_ra_rtr_pref: 0
  net.ipv6.conf.default.accept_redirects: 0
  net.ipv6.conf.default.accept_source_route: 0
  net.ipv6.conf.default.autoconf: 0
  net.ipv6.conf.default.dad_transmits: 0
  net.ipv6.conf.default.max_addresses: 1
  net.ipv6.conf.default.router_solicitations: 0
  net.ipv6.conf.default.use_tempaddr: 2

If disable_ipv6: true, IPv6 will be disabled and related sysctl settings configured.

ipv6_sysctl_settings is the sysctl configuration used if the host is using IPv6.

sysctl.conf

./defaults/main/journal.yml

rsyslog_filecreatemode: "0640"

journald_compress: true
journald_forwardtosyslog: false
journald_storage: persistent

rsyslog_filecreatemode sets the creation mode with which rsyslogd creates new files, see rsconf1_filecreatemode.

journald_compress can take a boolean value. If enabled (the default), data objects are compressed before they are written to the file system.

journald_storage controls where to store journal data. One of volatile, persistent, auto and none.

journald_forwardtosyslog control whether log messages received by the journal daemon shall be forwarded to a traditional syslog daemon.

See journald.conf for more information.

./defaults/main/kernel.yml

allow_virtual_system_calls: true
enable_page_poisoning: true
kernel_lockdown: false
page_table_isolation: true
slub_debugger_poisoning: false

allow_virtual_system_calls will allow virtual system calls if true else no vsyscall mapping will be set, see CONFIG_LEGACY_VSYSCALL_NONE.

enable_page_poisoning: true will enable CONFIG_PAGE_POISONING

kernel_lockdown configures the kernel lockdown feature. Valid values are false, true, integrity and confidentiality. If true, the kernel will be locked down in integrity mode.

page_table_isolation is a countermeasure against attacks on the shared user/kernel address space, see CONFIG_PAGE_TABLE_ISOLATION

slub_debugger_poisoning, if set to true, prevents many types of use-after-free vulnerabilities and it also prevents leak of data and detection of corrupted memory. See Short users guide for SLUB.

./defaults/main/limits.yml

limit_nofile_hard: 1024
limit_nofile_soft: 512
limit_nproc_hard: 1024
limit_nproc_soft: 512

Set maximum number of processes and open files, see limits.conf(5).

./defaults/main/#d.yml

logind:
  killuserprocesses: true
  killexcludeusers:
    - root
  idleaction: lock
  idleactionsec: 15min
  removeipc: true

Configure logind.

killuserprocesses takes a boolean argument. Configures whether the processes of a user should be killed when the user logs out.

killexcludeusers takes a list of usernames that override the killuserprocesses setting.

idleaction and idleactionsec configures the action to take when the system is idle and the delay after which the action configured in idleaction is taken.

removeipc takes a boolean argument. If enabled, the user may not consume IPC resources after the last of the user's sessions terminated.

./defaults/main/misc.yml

reboot_ubuntu: false
redhat_signing_keys:
  - 567E347AD0044ADE55BA8A5F199E2F91FD431D51
  - 47DB287789B21722B6D95DDE5326810137017186
epel7_signing_keys:
  - 91E97D7C4A5E96F17F3E888F6A2FAEA2352C64E5
epel8_signing_keys:
  - 94E279EB8D8F25B21810ADF121EA45AB2F86D6A1
epel9_signing_keys:
  - FF8AD1344597106ECE813B918A3872BF3228467C

If reboot_ubuntu: true an Ubuntu node will be rebooted if required.

redhat_signing_keys are the RedHat Product Signing Keys.

The epel7_signing_keys, epel8_signing_keys and epel9_signing_keys are release specific Fedora EPEL signing keys.

./defaults/main/module_blocklists.yml

fs_modules_blocklist:
  - cramfs
  - freevxfs
  - hfs
  - hfsplus
  - jffs2
  - squashfs
  - udf

misc_modules_blocklist:
  - bluetooth
  - bnep
  - btusb
  - can
  - cpia2
  - firewire-core
  - floppy
  - ksmbd
  - n_hdlc
  - net-pf-31
  - pcspkr
  - soundcore
  - thunderbolt
  - usb-midi
  - usb-storage
  - uvcvideo
  - v4l2_common

net_modules_blocklist:
  - atm
  - dccp
  - sctp
  - rds
  - tipc

Kernel modules to be blacklisted and disabled using a fake install.

Note

Disabling the usb-storage module will disable all USB storage devices. If such devices are needed USBGuard, or a similar tool, should be configured accordingly.

./defaults/main/mount.yml

hide_pid: 2
process_group: root

hide_pid sets /proc/<pid>/ access mode.

The process_group setting configures the group authorized to learn processes information otherwise prohibited by hidepid=.

/proc mount options

./defaults/main/ntp.yml

manage_timesyncd: true

fallback_ntp:
  - ntp.netnod.se
  - ntp.ubuntu.com
ntp:
  - 2.pool.ntp.org
  - time.nist.gov

If manage_timesyncd: true, then configure systemd timesyncd, otherwise installing a NTP client is recommended.

./defaults/main/packagemgmt.yml

apt_hardening_options:
  - Acquire::AllowDowngradeToInsecureRepositories "false";
  - Acquire::AllowInsecureRepositories "false";
  - Acquire::http::AllowRedirect "false";
  - APT::Get::AllowUnauthenticated "false";
  - APT::Get::AutomaticRemove "true";
  - APT::Install-Recommends "false";
  - APT::Install-Suggests "false";
  - APT::Periodic::AutocleanInterval "7";
  - APT::Sandbox::Seccomp "1";
  - Unattended-Upgrade::Remove-Unused-Dependencies "true";
  - Unattended-Upgrade::Remove-Unused-Kernel-Packages "true";

Configure the APT suite of tools.

./defaults/main/packages.yml

system_upgrade: true

packages_blocklist:
  - apport*
  - autofs
  - avahi*
  - avahi-*
  - beep
  - git
  - pastebinit
  - popularity-contest
  - prelink
  - rpcbind
  - rsh*
  - rsync
  - talk*
  - telnet*
  - tftp*
  - tuned
  - whoopsie
  - xinetd
  - yp-tools
  - ypbind

packages_debian:
  - acct
  - apparmor-profiles
  - apparmor-utils
  - apt-show-versions
  - audispd-plugins
  - auditd
  - cracklib-runtime
  - debsums
  - gnupg2
  - haveged
  - libpam-apparmor
  - libpam-cap
  - libpam-modules
  - libpam-pwquality
  - libpam-tmpdir
  - lsb-release
  - needrestart
  - openssh-server
  - postfix
  - rsyslog
  - sysstat
  - systemd-journal-remote
  - tcpd
  - vlock
  - wamerican

packages_redhat:
  - audispd-plugins
  - audit
  - cracklib
  - gnupg2
  - haveged
  - libpwquality
  - openssh-server
  - needrestart
  - postfix
  - psacct
  - python3-dnf-plugin-post-transaction-actions
  - rsyslog
  - rsyslog-gnutls
  - systemd-journal-remote
  - vlock
  - words

packages_ubuntu:
  - fwupd
  - secureboot-db
  - snapd

system_upgrade: true will run apt upgrade or dnf update if required.

Packages to be installed depending of distribution and packages to be removed (packages_blocklist).

./defaults/main/password.yml

manage_faillock: true

faillock:
  admin_group: []
  audit: true
  deny: 5
  dir: /var/run/faillock
  even_deny_root: true
  fail_interval: 900
  local_users_only: true
  no_log_info: false
  nodelay: true
  root_unlock_time: 600
  silent: false
  unlock_time: 600

login_defs:
  login_retries: 5
  login_timeout: 60
  pass_max_days: 60
  pass_min_days: 1
  pass_warn_age: 7

password_remember: 5

pwquality:
  dcredit: -1
  dictcheck: 1
  dictpath: ""
  difok: 8
  enforce_for_root: true
  enforcing: 1
  gecoscheck: 1
  lcredit: -1
  local_users_only: true
  maxclassrepeat: 4
  maxrepeat: 3
  minclass: 4
  minlen: 15
  ocredit: -1
  retry: 3
  ucredit: -1
  usercheck: 1
  usersubstr: 3

manage_faillock: true will enable the faillock library.

password_remember set the size of the password history that the user will not be able to reuse.

The variables faillock, login_defs and pwquality are used to configure the pam_faillock, login.defs and libpwquality.

./defaults/main/rkhunter.yml

manage_rkhunter: true

rkhunter_allow_ssh_prot_v1: false
rkhunter_allow_ssh_root_user: false
rkhunter_mirrors_mode: "0"
rkhunter_update_mirrors: true
rkhunter_web_cmd: curl -fsSL

If manage_rkhunter: true, then configure rkhunter.

./defaults/main/sshd.yml

manage_ssh: true

sshd_accept_env: LANG LC_*
sshd_admin_net:
  - 192.168.0.0/24
  - 192.168.1.0/24
sshd_allow_agent_forwarding: false
sshd_allow_groups:
  - sudo
sshd_allow_tcp_forwarding: false
sshd_allow_users:
  - "{{ ansible_user | default(lookup('ansible.builtin.env', 'USER')) }}"
sshd_authentication_methods: any
sshd_authorized_principals_file: /etc/ssh/auth_principals/%u
sshd_banner: /etc/issue.net
sshd_ca_signature_algorithms:
  - ecdsa-sha2-nistp256
  - ecdsa-sha2-nistp384
  - ecdsa-sha2-nistp521
  - ssh-ed25519
  - rsa-sha2-256
  - rsa-sha2-512
  - ssh-rsa
sshd_kbd_interactive_authentication: false
sshd_ciphers:
  - chacha20-poly1305@openssh.com
  - aes256-gcm@openssh.com
  - aes256-ctr
sshd_client_alive_count_max: 1
sshd_client_alive_interval: 200
sshd_compression: false
sshd_config_d_force_clear: false
sshd_config_force_replace: false
sshd_debian_banner: false
sshd_deny_groups: []
sshd_deny_users: []
sshd_gssapi_authentication: false
sshd_host_key_algorithms:
  - ssh-ed25519-cert-v01@openssh.com
  - ssh-rsa-cert-v01@openssh.com
  - ssh-ed25519
  - ssh-rsa
  - ecdsa-sha2-nistp521-cert-v01@openssh.com
  - ecdsa-sha2-nistp384-cert-v01@openssh.com
  - ecdsa-sha2-nistp256-cert-v01@openssh.com
  - ecdsa-sha2-nistp521
  - ecdsa-sha2-nistp384
  - ecdsa-sha2-nistp256
sshd_host_keys_files: []
sshd_host_keys_group: root
sshd_host_keys_mode: "0600"
sshd_host_keys_owner: root
sshd_hostbased_authentication: false
sshd_ignore_rhosts: true
sshd_ignore_user_known_hosts: true
sshd_kerberos_authentication: false
sshd_kex_algorithms:
  - curve25519-sha256@libssh.org
  - ecdh-sha2-nistp521
  - ecdh-sha2-nistp384
  - ecdh-sha2-nistp256
  - diffie-hellman-group-exchange-sha256
sshd_listen:
  - 0.0.0.0
sshd_log_level: VERBOSE
sshd_login_grace_time: 20
sshd_macs:
  - hmac-sha2-512-etm@openssh.com
  - hmac-sha2-256-etm@openssh.com
  - hmac-sha2-512
  - hmac-sha2-256
sshd_match_addresses: {}
sshd_match_groups: {}
sshd_match_local_ports: {}
sshd_match_users: {}
sshd_max_auth_tries: 3
sshd_max_sessions: 3
sshd_max_startups: 10:30:60
sshd_password_authentication: false
sshd_permit_empty_passwords: false
sshd_permit_root_login: false
sshd_permit_tunnel: false
sshd_permit_user_environment: false
sshd_ports:
  - 22
sshd_print_last_log: true
sshd_print_motd: false
sshd_print_pam_motd: false
sshd_rekey_limit: 512M 1h
sshd_required_ecdsa_size: 521
sshd_required_rsa_size: 4096
sshd_sftp_enabled: true
sshd_sftp_only_chroot: true
sshd_sftp_only_chroot_dir: "%h"
sshd_sftp_only_group: ""
sshd_sftp_subsystem: internal-sftp -f LOCAL6 -l INFO
sshd_strict_modes: true
sshd_syslog_facility: AUTH
sshd_tcp_keep_alive: false
sshd_trusted_user_ca_keys_base64: ""
sshd_trusted_user_ca_keys_file: /etc/ssh/trusted-user-ca-keys.pem
sshd_update_moduli: false
sshd_use_dns: false
sshd_use_pam: true
sshd_use_privilege_separation: sandbox
sshd_x11_forwarding: false

If manage_ssh: true the SSH client and the SSH daemon will be configured.

Note

CASignatureAlgorithms, Ciphers, HostKeyAlgorithms, KexAlgorithms and MACs will be configured as defined by cryptographic policies if /etc/crypto-policies/config exists and set_crypto_policy: true.

For a explanation of the options not described below, please read https://man.openbsd.org/sshd_config.

Only the network(s) defined in sshd_admin_net are allowed to connect to sshd_ports. Note that additional rules need to be set up in order to allow access to additional services.

OpenSSH login is allowed only for users whose primary group or supplementary group list matches one of the patterns in sshd_allow_groups. OpenSSH login is also allowed for users in sshd_allow_users. To do the opposite and deny access, use the sshd_deny_groups and sshd_deny_users parameters, which in turn have priority over the previous parameters.

sshd_allow_agent_forwarding specifies whether ssh-agent(1) forwarding is permitted.

sshd_allow_tcp_forwarding specifies whether TCP forwarding is permitted. The available options are true or all to allow TCP forwarding, false to prevent all TCP forwarding, local to allow local (from the perspective of ssh(1)) forwarding only or remote to allow remote forwarding only.

sshd_authentication_methods specifies the authentication methods that must be successfully completed in order to grant access to a user.

sshd_log_level gives the verbosity level that is used when logging messages.

sshd_max_auth_tries and sshd_max_sessions specifies the maximum number of SSH authentication attempt s permitted per connection and the maximum number of open shell, login or subsystem (e.g. sftp) sessions permitted per network connection.

sshd_password_authentication specifies whether password authentication is allowed.

sshd_ports specifies the port(s) number that sshd(8) listens on.

sshd_required_rsa_size, RequiredRSASize, will only be set if SSH version is higher than 9.1.

sshd_config_d_force_clear force clear directory /etc/ssh/sshd_config.d. Default: false.

sshd_config_force_replace force replace configuration file /etc/ssh/sshd_config. Default: false.

Note

By default, the role checks whether the directory /etc/ssh/sshd_config.d exists and whether it is linked via the Include parameter in the /etc/ssh/sshd_config file, if so, an additional configuration file is created in / etc/ssh/sshd_config.d, if not, the /etc/ssh/sshd_config file is overwritten.

Warning

If any sshd_match_(users|groups|addresses|local_ports) or sshd_sftp_only_group parameters is set, the value true will be implicit.

sshd_host_keys_files host keys for sshd. If empty ['/etc/ssh/ssh_host_rsa_key', '/etc/ssh/ssh_host_ec dsa_key', '/etc/ssh/ssh_host_ed25519_key'] will be used, as far as supported by the installed sshd version.

sshd_host_keys_owner set owner of host keys for sshd.

sshd_host_keys_group set group of host keys for sshd.

sshd_host_keys_mode set permission of host keys for sshd.

sshd_match_users add a conditional block for users. If all of the criteria on the Match line are satisfied, the rules/parameters defined on the following lines override those set in the global section of th e config file, until either another Match line or the end of the file.

Expected configuration structure:

sshd_match_users:
  - user: <username>
    rules:
      - <parameter sshd> <value>
      - <parameter sshd> <value>

Example, allow ubuntu user access through password authentication and allow ansible user access without a banner:

sshd_match_users:
  - user: ubuntu
    rules:
      - AllowUsers ubuntu
      - AuthenticationMethods password
      - PasswordAuthentication yes
  - user: ansible
    rules:
      - AllowUsers ansible
      - Banner none

sshd_match_groups add a conditional block for groups. More details and examples in the parameter description sshd_match_users.

Expected configuration structure:

sshd_match_groups:
  - group: <groupname>
    rules:
      - <parameter sshd> <value>
      - <parameter sshd> <value>

sshd_match_addresses add a conditional block for adddresses. More details and examples in the parameter description sshd_match_users.

Expected configuration structure:

sshd_match_addresses:
  - address: <ip>
    rules:
      - <parameter sshd> <value>
      - <parameter sshd> <value>

sshd_match_local_ports add a conditional block for ports. More details and examples in the parameter description sshd_match_users.

Expected configuration structure:

sshd_match_ports:
  - port: <port>
    rules:
      - <parameter sshd> <value>
      - <parameter sshd> <value>

sshd_print_pam_motd specifies whether printing of the MOTD via pam.

sshd_sftp_enabled specifies whether enabled sftp configuration.

sshd_sftp_subsystem sets the subsystem for file transfer daemon.

sshd_sftp_only_group specifies the name of the group that will have access restricted to the sftp service only.

sshd_sftp_only_chroot specifies group access will be via chroot isolation.

sshd_sftp_only_chroot_dir specifies the chroot directory. Accepts the tokens %% (a literal %), %h (home directory of the user), and %u (username).

sshd_syslog_facility sets the facility code that is used when logging messages from sshd.

sshd_update_moduli, if set to true, will download a updated moduli file from the konstruktoid/ssh-moduli repository.

./defaults/main/suid_sgid_blocklist.yml

suid_sgid_permissions: true
suid_sgid_blocklist:
  - 7z
  - aa-exec
  - ab
  - agetty
  - alpine
  - ansible-playbook
  - ansible-test
  - aoss
  - apt
  - apt-get
  [...]

If suid_sgid_permissions: true loop through suid_sgid_blocklist and remove any SUID/SGID permissions.

A complete file list is available in defaults/main/suid_sgid_blocklist.yml and is based on the work by @GTFOBins.

./defaults/main/sysctl.yml

manage_sysctl: true
sysctl_conf_dir: "{{ '/usr/lib/sysctl.d' if usr_lib_sysctl_d_dir else '/etc/sysctl.d' }}"

sysctl_dev_tty_ldisc_autoload: 0

ipv4_sysctl_settings:
  net.ipv4.conf.all.accept_redirects: 0
  net.ipv4.conf.all.accept_source_route: 0
  net.ipv4.conf.all.log_martians: 1
  net.ipv4.conf.all.rp_filter: 1
  net.ipv4.conf.all.secure_redirects: 0
  net.ipv4.conf.all.send_redirects: 0
  net.ipv4.conf.all.shared_media: 0
  net.ipv4.conf.default.accept_redirects: 0
  net.ipv4.conf.default.accept_source_route: 0
  net.ipv4.conf.default.log_martians: 1
  net.ipv4.conf.default.rp_filter: 1
  net.ipv4.conf.default.secure_redirects: 0
  net.ipv4.conf.default.send_redirects: 0
  net.ipv4.conf.default.shared_media: 0
  net.ipv4.icmp_echo_ignore_broadcasts: 1
  net.ipv4.icmp_ignore_bogus_error_responses: 1
  net.ipv4.ip_forward: 0
  net.ipv4.tcp_challenge_ack_limit: 2147483647
  net.ipv4.tcp_invalid_ratelimit: 500
  net.ipv4.tcp_max_syn_backlog: 20480
  net.ipv4.tcp_rfc1337: 1
  net.ipv4.tcp_syn_retries: 5
  net.ipv4.tcp_synack_retries: 2
  net.ipv4.tcp_syncookies: 1

generic_sysctl_settings:
  fs.protected_fifos: 2
  fs.protected_hardlinks: 1
  fs.protected_symlinks: 1
  fs.suid_dumpable: 0
  kernel.core_pattern: "|/bin/false"
  kernel.core_uses_pid: 1
  kernel.dmesg_restrict: 1
  kernel.kptr_restrict: 2
  kernel.panic: 60
  kernel.panic_on_oops: 60
  kernel.perf_event_paranoid: 3
  kernel.randomize_va_space: 2
  kernel.sysrq: 0
  kernel.unprivileged_bpf_disabled: 1
  kernel.yama.ptrace_scope: 2
  net.core.bpf_jit_harden: 2
  user.max_user_namespaces: 62967

conntrack_sysctl_settings:
  net.netfilter.nf_conntrack_max: 2000000
  net.netfilter.nf_conntrack_tcp_loose: 0

If manage_sysctl: true, then update the sysctl configuration.

sysctl_conf_dir is where the sysctl configuration will be placed.

See sysctl.conf and the kernel documentation.

./defaults/main/templates.yml

adduser_conf_template: etc/adduser.conf.j2
common_account_template: etc/pam.d/common-account.j2
common_auth_template: etc/pam.d/common-auth.j2
common_password_template: etc/pam.d/common-password.j2
coredump_conf_template: etc/systemd/coredump.conf.j2
faillock_conf_template: etc/security/faillock.conf.j2
hardening_rules_template: etc/audit/rules.d/hardening.rules.j2
hosts_allow_template: etc/hosts.allow.j2
hosts_deny_template: etc/hosts.deny.j2
initpath_sh_template: etc/profile.d/initpath.sh.j2
issue_template: etc/issue.j2
journald_conf_template: etc/systemd/journald.conf.j2
limits_conf_template: etc/security/limits.conf.j2
login_defs_template: etc/#.defs.j2
login_template: etc/pam.d/#.j2
logind_conf_template: etc/systemd/#d.conf.j2
logrotate_conf_template: etc/logrotate.conf.j2
motd_template: etc/motd.j2
pwquality_conf_template: etc/security/pwquality.conf.j2
resolved_conf_template: etc/systemd/resolved.conf.j2
rkhunter_template: etc/default/rkhunter.j2
ssh_config_template: etc/ssh/ssh_config.j2
sshd_config_template: etc/ssh/sshd_config.j2
sshd_tmpfiles_template: usr/lib/tmpfiles.d/ssh.conf.j2
sysctl_ipv6_config_template: etc/sysctl/sysctl.ipv6.conf.j2
sysctl_main_config_template: etc/sysctl/sysctl.main.conf.j2
system_conf_template: etc/systemd/system.conf.j2
timesyncd_conf_template: etc/systemd/timesyncd.conf.j2
tmp_mount_template: etc/systemd/tmp.mount.j2
unattended_upgrades_template: etc/apt/apt.conf.d/50unattended-upgrades.j2
user_conf_template: etc/systemd/user.conf.j2
useradd_template: etc/default/useradd.j2

Paths in order to support overriding the default role templates.

./defaults/main/ufw.yml

manage_ufw: true

ufw_outgoing_traffic:
  - 22
  - 53
  - 80
  - 123
  - 443
  - 853

ufw_rate_limit: false

See the note regarding required comments.

manage_ufw: true installs and configures ufw with related rules. Set it to false in order to install and configure a firewall manually.

ufw_outgoing_traffic opens the specific ufw ports, allowing outgoing traffic.

ufw_rate_limit, if true, will set connection rate limiting on all available physical network interfaces.

./defaults/main/umask.yml

session_timeout: 900
umask_value: "077"

session_timeout sets, in seconds, the TMOUT environment variable if systemd version is 252 or lower.

If systemd version is higher than 252, the session_timeout value will be set as StopIdleSessionSec.

umask_value sets the default umask value.

./defaults/main/usbguard.yml

manage_usbguard: true

usbguard_configuration_file: /etc/usbguard/usbguard-daemon.conf
usbguard_rulefile: /etc/usbguard/rules.conf

usbguard_auditbackend: LinuxAudit
usbguard_auditfilepath: /var/log/usbguard/usbguard-audit.log
usbguard_authorizeddefault: none
usbguard_devicemanagerbackend: uevent
usbguard_deviceruleswithport: false
usbguard_hidepii: false
usbguard_implicitpolicytarget: block
usbguard_inserteddevicepolicy: apply-policy
usbguard_ipcaccesscontrolfiles: /etc/usbguard/IPCAccessControl.d/
usbguard_ipcallowedgroups:
  - plugdev
  - root
  - wheel
usbguard_ipcallowedusers:
  - root
usbguard_presentcontrollerpolicy: keep
usbguard_presentdevicepolicy: apply-policy
usbguard_restorecontrollerdevicestate: false

manage_usbguard: true installs and configures USBGuard.

A policy will be generated if any rules can be listed and a policy doesn't yet exist.

See the configuration documentation regarding the available options.

./defaults/main/users.yml

delete_users:
  - games
  - gnats
  - irc
  - list
  - news
  - sync
  - uucp

Users to be removed.

Recommended Reading

Comparing the DISA STIG and CIS Benchmark values

Center for Internet Security Linux Benchmarks

Common Configuration Enumeration

DISA Security Technical Implementation Guides

SCAP Security Guides

Security focused systemd configuration

Contributing

Do you want to contribute? Great! Contributions are always welcome, no matter how large or small. If you found something odd, feel free to submit a issue, improve the code by creating a pull request, or by sponsoring this project.

License

Apache License Version 2.0

Author Information

https://github.com/konstruktoid