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diff --git a/content/blog/2023-10-15-alpine-ssh-hardening.md b/content/blog/2023-10-15-alpine-ssh-hardening.md deleted file mode 100644 index e1c555c..0000000 --- a/content/blog/2023-10-15-alpine-ssh-hardening.md +++ /dev/null @@ -1,74 +0,0 @@ -+++ -date = 2023-10-15 -title = "SSH Hardening for Alpine Linux" -description = "A quick guide to harden SSH configuration on Alpine." -+++ - -## Overview - -This guide follows the standard -[ssh-audit](https://www.ssh-audit.com/hardening_guides.html) hardening -guide, tweaked for Alpine Linux. - -## Hardening Guide - -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 -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 -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 -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 -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 -echo -e "Include /etc/ssh/sshd_config.d/*.conf" > /etc/ssh/sshd_config -``` - -6. Restart OpenSSH server - -```sh -rc-service sshd restart -``` - -## Testing SSH - -You can test the results with the `ssh-audit` python script. - -```sh -pip3 install ssh-audit -ssh-audit localhost -``` - -If everything succeeded, the results will show as all green. If anything -is yellow, orange, or red, you may need to tweak additional settings. - -```txt -#+caption: ssh audit -``` - - |