apf_portal/docs/setup/scripts/70-hardening.sh

#!/usr/bin/env bash
# Best-effort VM hardening — probes current state, only applies what's missing.
# Skips cleanly when infra has already configured a step.
#   - UFW (allow SSH only)
#   - unattended-upgrades (security channel)
#   - fail2ban
#   - sshd: disable root login + password auth (always validates first)
set -euo pipefail
# shellcheck source=./lib.sh
source "$(cd "$(dirname "$0")" && pwd)/lib.sh"
require_debian
require_not_root

log "Hardening pass — each section probes and skips if already done."

# ─── 1. UFW ────────────────────────────────────────────────────────────
if ! command -v ufw >/dev/null; then
  apt_install ufw
fi
if sudo ufw status | head -1 | grep -q 'Status: active'; then
  skip "UFW already active. Current rules:"
  sudo ufw status numbered | sed 's/^/    /'
else
  if confirm "Enable UFW with 'deny incoming, allow SSH'?"; then
    sudo ufw default deny incoming >/dev/null
    sudo ufw default allow outgoing >/dev/null
    sudo ufw allow OpenSSH >/dev/null
    sudo ufw --force enable
    ok "UFW enabled (SSH-only ingress)."
  else
    skip "UFW left disabled."
  fi
fi

# ─── 2. unattended-upgrades ────────────────────────────────────────────
apt_install unattended-upgrades
AUTO_UP="/etc/apt/apt.conf.d/20auto-upgrades"
if [[ -f "$AUTO_UP" ]] \
   && sudo grep -q 'APT::Periodic::Update-Package-Lists "1"' "$AUTO_UP" \
   && sudo grep -q 'APT::Periodic::Unattended-Upgrade "1"' "$AUTO_UP"; then
  skip "unattended-upgrades already enabled."
else
  cat <<'EOF' | sudo tee "$AUTO_UP" >/dev/null
APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";
EOF
  ok "unattended-upgrades enabled."
fi

# ─── 3. fail2ban (opt-in) ──────────────────────────────────────────────
# Some VMs already ship with infra-managed brute-force protection at the
# network layer (corp firewall, ACLs, etc.). In that case fail2ban on the
# host is redundant — and its presence can be the wrong layer to debug
# from when a rule misfires. Make it a deliberate choice instead of
# imposing it.
if systemctl is-active fail2ban.service >/dev/null 2>&1; then
  skip "fail2ban already running."
elif dpkg -s fail2ban >/dev/null 2>&1; then
  if confirm "fail2ban is installed but not running. Enable + start it now?"; then
    sudo systemctl enable --now fail2ban.service
    ok "fail2ban started + enabled at boot."
  else
    skip "fail2ban left stopped (user choice)."
  fi
else
  if confirm "Install + enable fail2ban (SSH brute-force protection)?"; then
    apt_install fail2ban
    sudo systemctl enable --now fail2ban.service
    ok "fail2ban installed + started + enabled at boot."
  else
    skip "fail2ban not installed (user choice)."
  fi
fi

# ─── 4. sshd hardening ────────────────────────────────────────────────
# Drop-in file rather than editing /etc/ssh/sshd_config directly.
# We always validate with `sshd -t` before reloading the daemon.
SSHD_DROPIN="/etc/ssh/sshd_config.d/99-apf-portal-hardening.conf"
if sudo test -f "$SSHD_DROPIN"; then
  skip "sshd hardening drop-in already at $SSHD_DROPIN."
else
  warn "About to disable password auth + root login on SSH."
  warn "Make sure your SSH key already works from your workstation."
  if confirm "Continue?"; then
    cat <<'EOF' | sudo tee "$SSHD_DROPIN" >/dev/null
# Managed by docs/setup/scripts/70-hardening.sh.
# To override or extend, drop another file in /etc/ssh/sshd_config.d/.
PermitRootLogin no
PasswordAuthentication no
ChallengeResponseAuthentication no
KbdInteractiveAuthentication no
UsePAM yes
AllowAgentForwarding yes
EOF
    if sudo sshd -t 2>/dev/null; then
      sudo systemctl reload ssh.service 2>/dev/null || sudo systemctl reload sshd.service
      ok "sshd reloaded with hardened config."
    else
      err "sshd config validation failed — removing $SSHD_DROPIN."
      sudo rm -f "$SSHD_DROPIN"
      exit 1
    fi
  else
    skip "sshd hardening declined."
  fi
fi

ok "Hardening pass complete."