#!/bin/bash
# SPDX-Version: 3.0
# SPDX-CreationInfo: 2025-06-17; WEIDNER, Marc S.; <msw@coresecret.dev>
# SPDX-ExternalRef: GIT https://git.coresecret.dev/msw/CISS.debian.installer.git
# SPDX-FileContributor: WEIDNER, Marc S.; Centurion Intelligence Consulting Agency
# SPDX-FileCopyrightText: 2024-2025; WEIDNER, Marc S.; <msw@coresecret.dev>
# SPDX-FileType: SOURCE
# SPDX-License-Identifier: EUPL-1.2 OR LicenseRef-CCLA-1.0
# SPDX-LicenseComment: This file is part of the CISS.debian.installer.secure framework.
# SPDX-PackageName: CISS.debian.installer
# SPDX-Security-Contact: security@coresecret.eu

guard_sourcing

#######################################
# Hardening 'fail2ban'.
# Globals:
#   ARY_ALLOW_IPV4
#   ARY_ALLOW_IPV6
#   RECOVERY
#   TARGET
#   VAR_FINAL_FQDN
#   VAR_FINAL_IPV4
#   VAR_FINAL_IPV6
#   VAR_LINK_IPV6
#   VAR_PROVIDER
#   VAR_RUN_RECOVERY
#   VAR_SSH_PORT
# Arguments:
#   None
# Returns:
#   0: on success
#######################################
hardening_fail2ban() {
  ### Declare Arrays, HashMaps, and Variables.
  declare -r  var_logfile="/root/.ciss/cdi/log/4420_hardening_fail2ban.log"
  declare     var_target="${TARGET}"

  ### Check for TARGET / RECOVERY.
  [[ "${VAR_RUN_RECOVERY}" == "true" ]] && var_target="${RECOVERY}"

  chroot_logger "${var_target}${var_logfile}"

  mkdir -p "${var_target}/root/.ciss/cdi/backup/etc/fail2ban/jail.d"
  cp "${var_target}/etc/fail2ban/fail2ban.conf" "${var_target}/root/.ciss/cdi/backup/etc/fail2ban/fail2ban.conf.bak"
  mv "${var_target}/etc/fail2ban/jail.d/defaults-debian.conf" "${var_target}/root/.ciss/cdi/backup/etc/fail2ban/jail.d/defaults-debian.conf.bak"

  # https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1024305
  insert_header   "${var_target}/etc/fail2ban/fail2ban.local"
  insert_comments "${var_target}/etc/fail2ban/fail2ban.local"
  cat << 'EOF' >> "${var_target}/etc/fail2ban/fail2ban.local"
[DEFAULT]
allowipv6             = auto

EOF

  insert_header   "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"
  insert_comments "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"

  if [[ "${#ARY_ALLOW_IPV4[@]}" -gt 0 ]]; then

    ### fail2ban ufw aggressive mode, one attempt for jumphost configuration.
    cat << EOF >> "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"
[DEFAULT]
dbpurgeage            = 384d
#                       127.0.0.1/8 - IPv4 loopback range (local host)
#                       ::1/128     - IPv6 loopback
#                       fe80::/10   - IPv6 link-local (on-link only; NDP/RA/DAD)
#                       ff00::/8    - IPv6 multicast (not an unicast host)
#                       ::/128      - IPv6 unspecified (all zeros; never a real peer)
ignoreip              = 127.0.0.1/8 ::1/128 fe80::/10 ff00::/8 ::/128
# ${VAR_FINAL_FQDN}
  ${VAR_FINAL_IPV4}
EOF

    if [[ "${VAR_LINK_IPV6}" == "true" ]]; then

      cat << EOF >> "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"
  ${VAR_FINAL_IPV6}/64
EOF
    fi

    cat << EOF >> "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"
# Jumphost
  ${ARY_ALLOW_IPV4[*]}
EOF

    if [[ "${VAR_LINK_IPV6}" == "true" ]]; then

      cat << EOF >> "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"
  ${ARY_ALLOW_IPV6[*]}
EOF
    fi

    cat << EOF >> "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"
usedns                = yes

[recidive]
enabled               = true
banaction             = ufw[blocktype=deny]
bantime               = 8d
bantime.increment     = true
bantime.factor        = 1
bantime.maxtime       = 128d
bantime.multipliers   = 1 2 4 8 16
bantime.overalljails  = true
bantime.rndtime       = 877s
filter                = recidive
findtime              = 16d
logpath               = /var/log/fail2ban/fail2ban.log*
maxretry              = 3

[sshd]
enabled               = true
backend               = systemd
bantime               = 1h
bantime.increment     = true
bantime.factor        = 1
bantime.maxtime       = 16d
bantime.multipliers   = 1 2 4 8 16 32 64 128 256 384
bantime.overalljails  = true
bantime.rndtime       = 877s
filter                = sshd
findtime              = 16m
mode                  = aggressive
port                  = ${VAR_SSH_PORT}
protocol              = tcp
maxretry              = 4

#
# CISS aggressive approach:
# Any valid client communicating with our server should be going directly to the service ports opened in ufw (ssh, 80, ...).
# Any client touching other ports is treated as malicious and therefore should be blocked access to ALL ports after 1 attempt.
# There is no necessity to ping our servers excessively. Any client pinging us more than 1 times will be blocked.
#

[icmp]
enabled               = true
banaction             = ufw[blocktype=deny]
bantime               = 1h
bantime.increment     = true
bantime.factor        = 1
bantime.maxtime       = 16d
bantime.multipliers   = 1 2 4 8 16 32 64 128 256 384
bantime.overalljails  = true
bantime.rndtime       = 877s
filter                = ciss-icmp
findtime              = 16m
logpath               = /var/log/ufw.log
maxretry              = 1

[ufw]
enabled               = true
banaction             = ufw[blocktype=deny]
bantime               = 1h
bantime.increment     = true
bantime.factor        = 1
bantime.maxtime       = 16d
bantime.multipliers   = 1 2 4 8 16 32 64 128 256 384
bantime.overalljails  = true
bantime.rndtime       = 877s
filter                = ciss-ufw
findtime              = 16m
logpath               = /var/log/ufw.log
maxretry              = 1

# vim: number et ts=2 sw=2 sts=2 ai tw=128 ft=conf
EOF

  else

    ### fail2ban ufw aggressive mode, 32 attempts for NO jumphost configuration.
    cat << EOF >> "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"
[DEFAULT]
dbpurgeage            = 384d
#                       127.0.0.1/8 - IPv4 loopback range (local host)
#                       ::1/128     - IPv6 loopback
#                       fe80::/10   - IPv6 link-local (on-link only; NDP/RA/DAD)
#                       ff00::/8    - IPv6 multicast (not an unicast host)
#                       ::/128      - IPv6 unspecified (all zeros; never a real peer)
ignoreip              = 127.0.0.1/8 ::1/128 fe80::/10 ff00::/8 ::/128
# ${VAR_FINAL_FQDN}
  ${VAR_FINAL_IPV4}
EOF

    if [[ "${VAR_LINK_IPV6}" == "true" ]]; then

      cat << EOF >> "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"
  ${VAR_FINAL_IPV6}/64
EOF
    fi

    cat << EOF >> "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"
usedns                = yes

[recidive]
enabled               = true
banaction             = ufw[blocktype=deny]
bantime               = 8d
bantime.increment     = true
bantime.factor        = 1
bantime.maxtime       = 128d
bantime.multipliers   = 1 2 4 8 16
bantime.overalljails  = true
bantime.rndtime       = 877s
filter                = recidive
findtime              = 16d
logpath               = /var/log/fail2ban/fail2ban.log*
maxretry              = 3

[sshd]
enabled               = true
backend               = systemd
bantime               = 1h
bantime.increment     = true
bantime.factor        = 1
bantime.maxtime       = 16d
bantime.multipliers   = 1 2 4 8 16 32 64 128 256 384
bantime.overalljails  = true
bantime.rndtime       = 877s
filter                = sshd
findtime              = 16m
mode                  = normal
port                  = ${VAR_SSH_PORT}
protocol              = tcp
maxretry              = 4

#
# CISS aggressive approach:
# Any valid client communicating with our server should be going directly to the service ports opened in ufw (ssh, 80, ...).
# Any client touching other ports is treated as malicious and therefore should be blocked access to ALL ports after 3 attempts.
# There is no necessity to ping our servers excessively. Any client pinging us more than 3 times will be blocked.
#

[icmp]
enabled               = true
banaction             = ufw[blocktype=deny]
bantime               = 1h
bantime.increment     = true
bantime.factor        = 1
bantime.maxtime       = 16d
bantime.multipliers   = 1 2 4 8 16 32 64 128 256 384
bantime.overalljails  = true
bantime.rndtime       = 877s
filter                = ciss-icmp
findtime              = 16m
logpath               = /var/log/ufw.log
maxretry              = 3

[ufw]
enabled               = true
banaction             = ufw[blocktype=deny]
bantime               = 1h
bantime.increment     = true
bantime.factor        = 1
bantime.maxtime       = 16d
bantime.multipliers   = 1 2 4 8 16 32 64 128 256 384
bantime.overalljails  = true
bantime.rndtime       = 877s
filter                = ciss-ufw
findtime              = 16m
logpath               = /var/log/ufw.log
maxretry              = 3

# vim: number et ts=2 sw=2 sts=2 ai tw=128 ft=conf
EOF

  fi

  ### Provider Hetzner needs special ignoreip rules.
  if [[ "${VAR_PROVIDER}" == "hetzner" ]]; then

    sed -i '0,/^maxretry/{s/^maxretry/# Hetzner Intern\n  172.31.1.1\/16\n&/}' "${var_target}/etc/fail2ban/jail.d/ciss-default.conf"

  fi

  insert_header   "${var_target}/etc/fail2ban/filter.d/ciss-icmp.conf"
  insert_comments "${var_target}/etc/fail2ban/filter.d/ciss-icmp.conf"
  cat << EOF >>   "${var_target}/etc/fail2ban/filter.d/ciss-icmp.conf"
[Definition]
# Generic ICMP/ICMPv6 blocks
failregex             = ^.*UFW (?:BLOCK|REJECT).*?\bSRC=<HOST>\b.*?\bPROTO=ICMP\b.*$
                        ^.*UFW (?:BLOCK|REJECT).*?\bSRC=<HOST>\b.*?\bPROTO=ICMPv6\b.*$

# vim: number et ts=2 sw=2 sts=2 ai tw=128 ft=conf
EOF

  insert_header   "${var_target}/etc/fail2ban/filter.d/ciss-ufw.conf"
  insert_comments "${var_target}/etc/fail2ban/filter.d/ciss-ufw.conf"
  cat << EOF >>   "${var_target}/etc/fail2ban/filter.d/ciss-ufw.conf"
[Definition]
# Match UFW BLOCK/REJECT with a source IP and *any* port field (SPT or DPT), protocol may be missing.
failregex             = ^.*UFW (?:BLOCK|REJECT).*?\bSRC=<HOST>\b.*?(?:\bDPT=\d+\b|\bSPT=\d+\b).*$
ignoreregex           =

# vim: number et ts=2 sw=2 sts=2 ai tw=128 ft=conf
EOF

  # Hardening of fail2ban systemd: https://wiki.archlinux.org/title/fail2ban#Service_hardening
  # The 'CapabilityBoundingSet' parameters 'CAP_DAC_READ_SEARCH' will allow fail2ban full read access to every directory and
  # file. "CAP_NET_ADMIN" and "CAP_NET_RAW" allow fail2ban to operate on any firewall that has a command-line shell interface.
  # By using 'ProtectSystem=strict' the filesystem hierarchy will only be read-only; 'ReadWritePaths' allows Fail2ban to have
  # write access on required paths.
  mkdir -p "${var_target}/etc/systemd/system/fail2ban.service.d"
  mkdir -p "${var_target}/var/log/fail2ban"

  insert_header   "${var_target}/etc/systemd/system/fail2ban.service.d/override.conf"
  insert_comments "${var_target}/etc/systemd/system/fail2ban.service.d/override.conf"
  cat << EOF >>   "${var_target}/etc/systemd/system/fail2ban.service.d/override.conf"
[Service]
PrivateDevices=yes
PrivateTmp=yes
ProtectHome=read-only
ProtectSystem=strict
ReadWritePaths=-/var/run/fail2ban
ReadWritePaths=-/var/lib/fail2ban
ReadWritePaths=-/var/log/fail2ban
ReadWritePaths=-/var/spool/postfix/maildrop
ReadWritePaths=-/run/xtables.lock
CapabilityBoundingSet=CAP_AUDIT_READ CAP_DAC_READ_SEARCH CAP_NET_ADMIN CAP_NET_RAW
ProtectClock=true
ProtectHostname=true
EOF

  cat << 'EOF' >> "${var_target}/etc/fail2ban/fail2ban.local"
[Definition]
logtarget             = /var/log/fail2ban/fail2ban.log

[Database]
# Keep entries for at least 384 days to cover recidive findtime.
dbpurgeage            = 384d

# vim: number et ts=2 sw=2 sts=2 ai tw=128 ft=conf
EOF

  ### Logrotate must be updated too.
  mkdir -p "${var_target}/root/.ciss/cdi/backup/etc/logrotate.d"
  cp "${var_target}/etc/logrotate.d/fail2ban" "${var_target}/root/.ciss/cdi/backup/etc/logrotate.d/fail2ban.bak"
  cat << EOF >| "${var_target}/etc/logrotate.d/fail2ban"
/var/log/fail2ban/fail2ban.log {
    daily
    rotate 384
    maxage 384
    notifempty
    dateext
    dateyesterday
    compress
    compresscmd /usr/bin/zstd
    compressext .zst
    compressoptions -20
    uncompresscmd /usr/bin/unzstd
    delaycompress
    shred
    missingok
    postrotate
        fail2ban-client flushlogs 1>/dev/null
    endscript
    # If fail2ban runs as non-root it still needs to have write access
    # to logfiles.
    # create 640 fail2ban adm
    create 640 root adm
}
EOF
  touch "${var_target}/var/log/fail2ban/fail2ban.log"
  chmod 0640 "${var_target}/var/log/fail2ban/fail2ban.log"

  if [[ ! -f "${var_target}/var/log/ufw.log" ]]; then
    install -d -m 0755 "${var_target}/var/log"
    : >| "${var_target}/var/log/ufw.log"
    chmod 0640 "${var_target}/var/log/ufw.log"
  fi

  ### Merge / Dump-Parse via 'fail2ban-client -d'. All '*.conf', '*.local', and 'jail.*'-files are read, inherited, and merged.
  ### Syntax, path, and key errors result in a non-zero exit.
  chroot_script "${var_target}" "
    fail2ban-client -d >> ${var_logfile} && echo "OK: config parsed" >> ${var_logfile} || echo "ERROR: config invalid" >> ${var_logfile}
  "

  guard_dir && return 0
}
### Prevents accidental 'unset -f'.
# shellcheck disable=SC2034
readonly -f hardening_fail2ban
# vim: number et ts=2 sw=2 sts=2 ai tw=128 ft=sh