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Created Proxmox VE 7.3-6 (markdown)

Clément Fiere 2023-02-24 11:22:39 +02:00
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Same instructions as [Ubuntu 22.04 LTS Server](https://www.ssh-audit.com/hardening_guides.html#ubuntu_22_04_lts),
except, remove `sntrup761x25519-sha512@openssh.com` from `KexAlgorithms` in step 4, as it is not supported out of the box.
That is :
__Note:__ all commands below are to be executed as the _root_ user.
### 0. Make a backup of your _ssh_ folder as a precaution
```
cp -r /etc/ssh /etc/_ssh.back
```
### 1. Re-generate the RSA and ED25519 keys
```
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
```
awk '$5 >= 3071' /etc/ssh/moduli > /etc/ssh/moduli.safe
mv /etc/ssh/moduli.safe /etc/ssh/moduli
```
### 3. Enable the RSA and ED25519 keys
Enable the RSA and ED25519 _HostKey_ directives in the `/etc/ssh/sshd_config` file:
```
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
```
cat <<EOF > /etc/ssh/sshd_config.d/ssh-audit_hardening.conf
# Restrict key exchange, cipher, and MAC algorithms, as per sshaudit.com
# hardening guide.
KexAlgorithms curve25519-sha256,curve25519-sha256@libssh.org,gss-curve25519-sha256-,diffie-hellman-group16-sha512,gss-group16-sha512-,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha256
Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
MACs hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,umac-128-etm@openssh.com
HostKeyAlgorithms 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
EOF
```
### 5. Restart OpenSSH server
```
service ssh restart
```