64 lines
2 KiB
Markdown
64 lines
2 KiB
Markdown
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---
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creation date: 2022-01-08
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tags: [note,archlinux,linux,security,ssh,iptables]
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---
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# SSH Guard, iptables
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## SSH
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Disable weak ciphers by adding the following to the `sshd_config` file:
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```
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# Disable weak ciphers
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KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group16-sha512,diffie-hellman-group14-sha256,diffie-hellman-group18-sha512
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MACs umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com
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HostKeyAlgorithms ssh-rsa,rsa-sha2-256,rsa-sha2-512
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```
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Be sure to disable password auth (`PasswordAuthentication no`) and set `PermitRootLogin yes`
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## iptables
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Install `sshguard`. To function properly, add a chain for it (ipv4 and ipv6). Don't forget to restart docker daemon if services don't work properly. Docker manipulates firewall rules.
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Ports `22` and `2222` will be monitored in this example.
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Also see [here](https://wiki.archlinux.org/index.php/Sshguard#iptables).
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```sh
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# IPv4
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iptables -N sshguard
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iptables -A INPUT -m multiport -p tcp --destination-ports 22,2222 -j sshguard
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iptables-save > /etc/iptables/iptables.rules
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# IPv6
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ip6tables -N sshguard
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ip6tables -A INPUT -m multiport -p tcp --destination-ports 22,2222 -j sshguard
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ip6tables-save > /etc/iptables/ip6tables.rules
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```
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Start with `systemctl enable --now sshguard` or restart afterwards with `systemctl restart sshguard` to apply or `ExecStartPre=` above in sshguard's systemd file.
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```sh
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ExecStartPre=/bin/bash -c '(while ! nc -z -v -w1 localhost 2222 > /dev/null; do echo "Waiting for port 2222 to open..."; sleep 15; done); sleep 10'
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```
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or create the following file and execute on every reboot with a certain, e.g. with
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```sh
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[Timer]
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OnBootSec=1min
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```
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```sh
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# IPv4
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iptables -N sshguard && \
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iptables -A INPUT -m multiport -p tcp --destination-ports 22,2222 -j sshguard && \
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iptables-save > /etc/iptables/iptables.rules
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# IPv6
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ip6tables -N sshguard && \
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ip6tables -A INPUT -m multiport -p tcp --destination-ports 22,2222 -j sshguard && \
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ip6tables-save > /etc/iptables/ip6tables.rules
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```
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