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diff --git a/blog/2023-10-15-alpine-ssh-hardening.org b/blog/2023-10-15-alpine-ssh-hardening.org index 2ba483d..03a3ba7 100644 --- a/blog/2023-10-15-alpine-ssh-hardening.org +++ b/blog/2023-10-15-alpine-ssh-hardening.org @@ -1,60 +1,74 @@ -+++ -date = 2023-10-16T00:20:45+00:00 -title = "SSH Hardening for Alpine Linux" -description = "A quick guide to hardening SSH on Alpine Linux." -+++ - -## Overview +#+title: SSH Hardening for Alpine Linux +#+date: 2023-10-16 +** Overview +:PROPERTIES: +:CUSTOM_ID: overview +:END: This guide follows the standard -[ssh-audit](https://www.ssh-audit.com/hardening_guides.html) hardening guide, -tweaked for Alpine Linux. - -## Hardening Guide +[[https://www.ssh-audit.com/hardening_guides.html][ssh-audit]] hardening +guide, tweaked for Alpine Linux. -These steps must be performed as root. You can try to use `doas` or `sudo`, -but there may be issues. +** Hardening Guide +:PROPERTIES: +:CUSTOM_ID: hardening-guide +:END: +These steps must be performed as root. You can try to use =doas= or +=sudo=, but there may be issues. 1. Re-generate the RSA and ED25519 keys -```sh + +#+begin_src sh rm /etc/ssh/ssh_host_* ssh-keygen -t rsa -b 4096 -f /etc/ssh/ssh_host_rsa_key -N "" ssh-keygen -t ed25519 -f /etc/ssh/ssh_host_ed25519_key -N "" -``` -2. Remove small Diffie-Hellman moduli -```sh +#+end_src + +2. [@2] Remove small Diffie-Hellman moduli + +#+begin_src sh awk '$5 >= 3071' /etc/ssh/moduli > /etc/ssh/moduli.safe mv /etc/ssh/moduli.safe /etc/ssh/moduli -``` -3. Enable the RSA and ED25519 HostKey directives in the /etc/ssh/sshd_config -file -```sh +#+end_src + +3. [@3] Enable the RSA and ED25519 HostKey directives in the + /etc/ssh/sshd_config file + +#+begin_src sh sed -i 's/^\#HostKey \/etc\/ssh\/ssh_host_\(rsa\|ed25519\)_key$/HostKey \/etc\/ssh\/ssh_host_\1_key/g' /etc/ssh/sshd_config -``` -4. Restrict supported key exchange, cipher, and MAC algorithms -```sh +#+end_src + +4. [@4] Restrict supported key exchange, cipher, and MAC algorithms + +#+begin_src sh echo -e "\n# Restrict key exchange, cipher, and MAC algorithms, as per sshaudit.com\n# hardening guide.\nKexAlgorithms sntrup761x25519-sha512@openssh.com,curve25519-sha256,curve25519-sha256@libssh.org,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha256\nCiphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr\nMACs hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,umac-128-etm@openssh.com\nHostKeyAlgorithms ssh-ed25519,ssh-ed25519-cert-v01@openssh.com,sk-ssh-ed25519@openssh.com,sk-ssh-ed25519-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256,rsa-sha2-256-cert-v01@openssh.com" > /etc/ssh/sshd_config.d/ssh-audit_hardening.conf -``` -5. Include the /etc/ssh/sshd_config.d directory -```sh +#+end_src + +5. [@5] Include the /etc/ssh/sshd_config.d directory + +#+begin_src sh echo -e "Include /etc/ssh/sshd_config.d/*.conf" > /etc/ssh/sshd_config -``` -6. Restart OpenSSH server -```sh -rc-service sshd restart -``` +#+end_src + +6. [@6] Restart OpenSSH server -## Testing SSH +#+begin_src sh +rc-service sshd restart +#+end_src -You can test the results with the `ssh-audit` python script. +** Testing SSH +:PROPERTIES: +:CUSTOM_ID: testing-ssh +:END: +You can test the results with the =ssh-audit= python script. -```sh +#+begin_src sh pip3 install ssh-audit ssh-audit localhost -``` +#+end_src -If everything succeeded, the results will show as all green. If anything is -yellow, orange, or red, you may need to tweak additional settings. +If everything succeeded, the results will show as all green. If anything +is yellow, orange, or red, you may need to tweak additional settings. -![ssh audit](https://img.cleberg.net/blog/20231015-ssh-hardening/ssh-audit.png -"ssh-audit") +#+caption: ssh audit +[[https://img.cleberg.net/blog/20231015-ssh-hardening/ssh-audit.png%20%22ssh-audit%22]] |