Marc S. Weidner
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Signed-off-by: Marc S. Weidner <msw@coresecret.dev>
67 lines
2.1 KiB
Bash
67 lines
2.1 KiB
Bash
#!/bin/sh
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# SPDX-Version: 3.0
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# SPDX-CreationInfo: 2025-06-17; WEIDNER, Marc S.; <msw@coresecret.dev>
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# SPDX-ExternalRef: GIT https://git.coresecret.dev/msw/CISS.debian.installer.git
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# SPDX-FileContributor: WEIDNER, Marc S.; Centurion Intelligence Consulting Agency
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# SPDX-FileCopyrightText: 2024-2025; ZIMNOL, Andre H.; <git.cs@physnet.eu>
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# SPDX-FileType: SOURCE
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# SPDX-License-Identifier: EUPL-1.2 OR LicenseRef-CCLA-1.0
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# SPDX-LicenseComment: This file is part of the CISS.debian.installer.secure framework.
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# SPDX-PackageName: CISS.debian.installer
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# SPDX-Security-Contact: security@coresecret.eu
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# shellcheck shell=sh
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# Firewall script for Dropbear SSH inside initramfs.
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# This script runs at the "init-bottom" stage of the early boot process.
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#
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# It configures basic iptables rules to restrict SSH access to Dropbear
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# while the system is in the pre-boot phase (before root is decrypted).
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#
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# IPv6 is not supported in initramfs at this stage due to complexity.
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# Only trusted IPv4 addresses are allowed.
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PREREQ="dropbear"
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prereqs() { echo "${PREREQ}"; }
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case "$1" in
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prereqs) prereqs; exit 0 ;;
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esac
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### Check if the firewall is enabled via the config file.
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DROPBEAR_FW_CONF="/etc/initramfs-tools/conf.d/dropbear_fw.cnf"
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if [ -f "${DROPBEAR_FW_CONF}" ]; then
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# shellcheck disable=SC1090
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. "${DROPBEAR_FW_CONF}"
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else
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DROPBEAR_FIREWALL_ENABLED=0
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fi
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### Abort if the firewall flag is not set or disabled.
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if [ "${DROPBEAR_FIREWALL_ENABLED}" != "1" ]; then
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echo "Dropbear firewall disabled by 'dropbear_fw.cnf'."
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exit 0
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fi
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### Ensure iptables is available.
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if command -v iptables >/dev/null 2>&1; then
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### Reset any existing rules.
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iptables -F
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iptables -X
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### Default policy: block everything unless explicitly allowed.
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iptables -P INPUT DROP
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iptables -P FORWARD DROP
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iptables -P OUTPUT ACCEPT
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### Allow local loopback.
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iptables -A INPUT -i lo -j ACCEPT
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### Infrastructure host / Jump-Server / VPN-Exit-Node: only allow SSH from the specified IPv4.
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iptables -A INPUT -p tcp --dport "${DROPBEAR_PORT}" -s "${DROPBEAR_JUMP_SERVER_IP}" -j ACCEPT
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fi
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# vim: number et ts=2 sw=2 sts=2 ai tw=128 ft=sh
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