Hardening - the Ansible role

An Ansible role to make a AlmaLinux, Debian, or Ubuntu server a bit more secure. systemd edition.

Requires Ansible >= 2.13.

Available on Ansible Galaxy.

AlmaLinux 8, AlmaLinux 9, Debian 11, Ubuntu 20.04 LTS (Focal Fossa) and Ubuntu 22.04 LTS (Jammy Jellyfish) are supported.

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.

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_port and ufw_outgoing_traffic variables.

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

install_aide: true
aide_checksums: sha512

If install_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.conf(5)

./defaults/main/auditd.yml

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_flush: sync
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

Enable auditd 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_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/compilers.yml

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

List of compilers that 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

dns: 127.0.0.1 1.1.1.1
fallback_dns: 9.9.9.9 1.0.0.1
dnssec: allow-downgrade
dns_over_tls: opportunistic

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.

systemd option.

./defaults/main/ipv6.yml

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

If disable_ipv6: true, IPv6 will be disabled.

./defaults/main/limits.yml

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

Maximum number of processes and open files.

./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 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

block_blacklisted: false
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

Blocked kernel modules.

Setting block_blacklisted: true will block, or disable, any automatic loading of blacklisted kernel modules. The reasoning behind this is that a blacklisted module can still be loaded manually with modprobe module_name. Using install module_name /bin/true prevents this.

This will affect modules that the distribution has blacklisted as part of its default setup, or that were added manually at some point, by anyone with access to your system. Please verify the affected modules before turning this on by running modprobe --showconfig | grep '^blacklist'

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

enable_timesyncd: true
fallback_ntp: 2.ubuntu.pool.ntp.org 3.ubuntu.pool.ntp.org
ntp: "0.ubuntu.pool.ntp.org 1.ubuntu.pool.ntp.org"
aws_fallback_ntp: "169.254.169.123"
aws_ntp: "169.254.169.123"

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

./defaults/main/packages.yml

system_upgrade: true
packages_blocklist:
  - apport*
# This package is required for freeipa-server on Fedora.
#   - autofs
# These packages are required for freeipa-server on Fedora.
#   - avahi*
#   - avahi-*
  - beep
  - git
  - pastebinit
  - popularity-contest
  - prelink
# This package is required for freeipa-server on Fedora.
#  - rpcbind
  - rsh*
  - rsync
  - talk*
  - telnet*
  - tftp*
  - tuned
  - whoopsie
  - xinetd
  - yp-tools
  - ypbind
packages_debian:
  # We are only installing packages needed to support the tasks being run.
  # - acct
  # - apparmor-profiles
  # - apparmor-utils
  # - apt-show-versions
  # - audispd-plugins
  - auditd
  - cracklib-runtime
  # - debsums
  # - gnupg2
  # - haveged
  # - libpam-apparmor
  # - libpam-cap
  # - libpam-modules
  # We are only installing this package as it provides /etc/security/pwquality.conf
  - libpam-pwquality
  # - libpam-tmpdir
  # - lsb-release
  # - needrestart
  # - openssh-server
  # - postfix
  # - rkhunter
  # - rsyslog
  # - sysstat
  # - systemd-journal-remote
  # - tcpd
  # - vlock
  # - wamerican
packages_redhat:
  # We are only installing packages needed to support the tasks being run.
  # - audispd-plugins
  - audit
  - cracklib
  # - gnupg2
  # - haveged
  - libpwquality
  # - openssh-server
  # - needrestart
  # - postfix
  # - psacct
  - python3-dnf-plugin-post-transaction-actions
  # - rkhunter
  # - rsyslog
  # - rsyslog-gnutls
  # - systemd-journal-remote
  # - vlock
  # - words
packages_ubuntu: []
  # We are only installing packages needed to support the tasks being run.
  # - fwupd
  # - secureboot-db
  # - snapd

system_upgrade: 'yes' 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

crypto_policy: "DEFAULT:NO-SHA1"
pwquality_config:
  dcredit: -1
  dictcheck: 1
  difok: 8
  enforcing: 1
  lcredit: -1
  maxclassrepeat: 4
  maxrepeat: 3
  minclass: 4
  minlen: 15
  ocredit: -1
  ucredit: -1

Configure the libpwquality library.

./defaults/main/sshd.yml

sshd_accept_env: LANG LC_*
sshd_admin_net:
  - 0.0.0.0/0
sshd_allow_agent_forwarding: "no"
sshd_allow_groups: sudo
sshd_allow_users: "{{ ansible_user }}"
sshd_allow_tcp_forwarding: "no"
sshd_authentication_methods: any
sshd_banner: /etc/issue.net
sshd_ca_signature_algorithms: >-
  ecdsa-sha2-nistp256,
  [email protected],
  ecdsa-sha2-nistp384,
  ecdsa-sha2-nistp521,
  ssh-ed25519,
  [email protected],
  rsa-sha2-256,
  rsa-sha2-512
sshd_challenge_response_authentication: "no"
sshd_ciphers: >-
  [email protected],
  [email protected],
  [email protected],
  aes256-ctr,
  aes192-ctr,
  aes128-ctr
sshd_client_alive_count_max: 3
sshd_client_alive_interval: 15
sshd_compression: "no"
sshd_gssapi_authentication: "no"
sshd_gssapi_kex_algorithms: >-
  gss-curve25519-sha256-,
  gss-nistp256-sha256-,
  gss-group14-sha256-,
  gss-group16-sha512-
sshd_hostbased_authentication: "no"
sshd_host_key_algorithms: >-
  [email protected],
  [email protected],
  ssh-ed25519,
  ssh-rsa,
  [email protected],
  [email protected],
  [email protected],
  ecdsa-sha2-nistp521,
  ecdsa-sha2-nistp384,
  ecdsa-sha2-nistp256
sshd_ignore_rhosts: "yes"
sshd_ignore_user_known_hosts: "yes"
sshd_kerberos_authentication: "no"
sshd_kex_algorithms: >-
  curve25519-sha256,
  [email protected],
  diffie-hellman-group14-sha256,
  diffie-hellman-group16-sha512,
  diffie-hellman-group18-sha512,
  ecdh-sha2-nistp521,
  ecdh-sha2-nistp384,
  ecdh-sha2-nistp256,
  diffie-hellman-group-exchange-sha256
sshd_login_grace_time: 20
sshd_log_level: VERBOSE
sshd_macs: >-
  [email protected],
  [email protected],
  hmac-sha2-512,
  hmac-sha2-256
sshd_max_auth_tries: 3
sshd_max_sessions: 4
sshd_max_startups: 10:30:60
sshd_password_authentication: "no"
sshd_permit_empty_passwords: "no"
sshd_permit_root_login: "no"
sshd_permit_user_environment: "no"
sshd_port: 22
sshd_print_last_log: "yes"
sshd_print_motd: "no"
sshd_pubkey_accepted_algorithms: >-
  ecdsa-sha2-nistp256,
  [email protected],
  [email protected],
  [email protected],
  ecdsa-sha2-nistp384,
  [email protected],
  ecdsa-sha2-nistp521,
  [email protected],
  ssh-ed25519,
  [email protected],
  [email protected],
  [email protected],
  rsa-sha2-256,
  [email protected],
  rsa-sha2-512,
  [email protected]
sshd_rekey_limit: 512M 1h
sshd_required_rsa_size: 2048
sshd_strict_modes: "yes"
sshd_subsystem: sftp internal-sftp
sshd_tcp_keep_alive: "no"
sshd_use_dns: "no"
sshd_use_pam: "yes"
sshd_x11_forwarding: "no"

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_port. 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.

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 yes or all to allow TCP forwarding, no 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 attempts 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_port specifies the port number that sshd(8) listens on.

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

./defaults/main/suid_sgid_blocklist.yml

suid_sgid_permissions: true
suid_sgid_blocklist:
  - 7z
  - ab
  - agetty
  - alpine
  - ansible-playbook
  - 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

sysctl_dev_tty_ldisc_autoload: 0
sysctl_net_ipv6_conf_accept_ra_rtr_pref: 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

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

generic_sysctl_settings:
  fs.protected_fifos: 2
  fs.protected_hardlinks: 1
  fs.protected_symlinks: 1
  fs.suid_dumpable: 0
  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

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

sysctl configuration.

sysctl.conf

./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
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
logind_conf_template: etc/systemd/logind.conf.j2
login_defs_template: etc/login.defs.j2
login_template: etc/pam.d/login.j2
logrotate_conf_template: etc/logrotate.conf.j2
motd_template: etc/motd.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
system_conf_template: etc/systemd/system.conf.j2
timesyncd_conf_template: etc/systemd/timesyncd.conf.j2
useradd_template: etc/default/useradd.j2
user_conf_template: etc/systemd/user.conf.j2

Paths in order to support overriding the default role templates.

./defaults/main/ufw.yml

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

ufw_enable: 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.

./defaults/main/umask.yml

umask_value: "027"

Set default umask value.

./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