SSH-Hardening: Unterschied zwischen den Versionen

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(Update ssh config for 2019 (Debian buster))
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SSH-Hardening, 2015-01-10, based on https://stribika.github.io/2015/01/04/secure-secure-shell.html (with a stripped down list of Ciphers and MACs)
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SSH-Hardening
  
=== Preparations ===
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based on https://stribika.github.io/2015/01/04/secure-secure-shell.html (with a stripped down list of Ciphers and MACs)
On Debian Stable (= Jessie) and Ubuntu 14.04 (= Trusty) you don't have to do anything)
 
 
 
On Debian Oldtable (= Wheezy):
 
 
 
echo "deb http://debian.inode.at/debian/ wheezy-backports main" >> /etc/apt/sources.list
 
apt-get update
 
apt-get -t wheezy-backports install openssh-server
 
 
 
On Ubuntu 12.04 (= Precise): To lazy and/or incompetent for backports.
 
  
 
=== Server configuration ===
 
=== Server configuration ===
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<pre>
 
<pre>
# SSH hardening, see https://stribika.github.io/2015/01/04/secure-secure-shell.html
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# SSH hardening, see https://fs.fsinf.at/wiki/SSH-Hardening
#    https://fs.fsinf.at/wiki/SSH-Hardening
 
  
 
# Disable SSHv1
 
# Disable SSHv1
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HostKey /etc/ssh/ssh_host_rsa_key
 
HostKey /etc/ssh/ssh_host_rsa_key
 
HostKey /etc/ssh/ssh_host_ed25519_key
 
HostKey /etc/ssh/ssh_host_ed25519_key
KexAlgorithms curve25519-sha256@libssh.org
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KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256
Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes256-ctr
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Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160
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MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com
 
</pre>
 
</pre>
  
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'''WARNING:''' This overwrites your old keys if you're not careful. If you don't add a new key to your servers before removing the old ones, you're locked out.
 
'''WARNING:''' This overwrites your old keys if you're not careful. If you don't add a new key to your servers before removing the old ones, you're locked out.
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=== Sources ===
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* https://cipherli.st/
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* '''old, from 2015:''' https://stribika.github.io/2015/01/04/secure-secure-shell.html

Version vom 20. Juli 2019, 15:04 Uhr

SSH-Hardening

based on https://stribika.github.io/2015/01/04/secure-secure-shell.html (with a stripped down list of Ciphers and MACs)

Server configuration

Remove all HostKey directives in /etc/ssh/sshd_config, then append at the bottom:

# SSH hardening, see https://fs.fsinf.at/wiki/SSH-Hardening

# Disable SSHv1
Protocol 2

# Only allow Public Key Authentication
PubkeyAuthentication yes
PasswordAuthentication no
ChallengeResponseAuthentication no

# Only allow users in the "users" group (no system users!).
# NOTE: See /etc/adduser.conf (EXTRA_GROUPS and ADD_EXTRA_GROUPS) to 
# automatically add new non-system users to a group.
AllowGroups users
 
# Don't forget to remove HostKey directives above
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
KexAlgorithms curve25519-sha256@libssh.org,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-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com

... and execute:

cd /etc/ssh/
rm ssh_host_*
ssh-keygen -t rsa -b 4096 -f ssh_host_rsa_key -N ""
ssh-keygen -t ed25519 -f ssh_host_ed25519_key -N ""
restart server

When restarting, current session is not affected, make sure you keep it open, in case you've done something wrong:

/etc/init.d/ssh restart

Client configuration

On top of your ~/.ssh/config, add:

Host *
KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1
Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes256-ctr
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-ripemd160-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160

Note that we add diffie-hellman-group-exchange-sha256 in comparison to the server config - this is for comparability with Ubuntu 12.04 (remove it if you don't care).

If possible, you can also regenerate your own SSH keys:

ssh-keygen -t ed25519 -o -a 100
ssh-keygen -t rsa -b 4096 -o -a 100

WARNING: This overwrites your old keys if you're not careful. If you don't add a new key to your servers before removing the old ones, you're locked out.

Sources