Created
February 15, 2019 11:40
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Hardened SSH configuration file for modern Linux servers
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# $OpenBSD: sshd_config,v 1.102 2018/02/16 02:32:40 djm Exp $ | |
# This is the sshd server system-wide configuration file. See | |
# sshd_config(5) for more information. | |
# This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin | |
# The strategy used for options in the default sshd_config shipped with | |
# OpenSSH is to specify options with their default value where | |
# possible, but leave them commented. Uncommented options override the | |
# default value. | |
#Port 22 | |
#AddressFamily any | |
#ListenAddress 0.0.0.0 | |
#ListenAddress :: | |
Protocol 2 | |
HostKey /etc/ssh/ssh_host_rsa_key | |
#HostKey /etc/ssh/ssh_host_ecdsa_key | |
HostKey /etc/ssh/ssh_host_ed25519_key | |
KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512 | |
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 | |
HostKeyAlgorithms ssh-ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-ed25519,ssh-rsa,ecdsa-sha2-nistp521-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp521,ecdsa-sha2-nistp384,ecdsa-sha2-nistp256 | |
# Ciphers and keying | |
#RekeyLimit default none | |
# Logging | |
#SyslogFacility AUTH | |
LogLevel VERBOSE | |
# Authentication: | |
#LoginGraceTime 2m | |
PermitRootLogin no | |
AuthenticationMethods publickey | |
#StrictModes yes | |
#MaxAuthTries 6 | |
#MaxSessions 10 | |
#PubkeyAuthentication yes | |
# Expect .ssh/authorized_keys2 to be disregarded by default in future. | |
#AuthorizedKeysFile .ssh/authorized_keys .ssh/authorized_keys2 | |
#AuthorizedPrincipalsFile none | |
#AuthorizedKeysCommand none | |
#AuthorizedKeysCommandUser nobody | |
# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts | |
#HostbasedAuthentication no | |
# Change to yes if you don't trust ~/.ssh/known_hosts for | |
# HostbasedAuthentication | |
#IgnoreUserKnownHosts no | |
# Don't read the user's ~/.rhosts and ~/.shosts files | |
#IgnoreRhosts yes | |
# To disable tunneled clear text passwords, change to no here! | |
PasswordAuthentication no | |
#PermitEmptyPasswords no | |
# Change to yes to enable challenge-response passwords (beware issues with | |
# some PAM modules and threads) | |
ChallengeResponseAuthentication no | |
# Kerberos options | |
#KerberosAuthentication no | |
#KerberosOrLocalPasswd yes | |
#KerberosTicketCleanup yes | |
#KerberosGetAFSToken no | |
# GSSAPI options | |
#GSSAPIAuthentication no | |
#GSSAPICleanupCredentials yes | |
#GSSAPIStrictAcceptorCheck yes | |
#GSSAPIKeyExchange no | |
# Set this to 'yes' to enable PAM authentication, account processing, | |
# and session processing. If this is enabled, PAM authentication will | |
# be allowed through the ChallengeResponseAuthentication and | |
# PasswordAuthentication. Depending on your PAM configuration, | |
# PAM authentication via ChallengeResponseAuthentication may bypass | |
# the setting of "PermitRootLogin without-password". | |
# If you just want the PAM account and session checks to run without | |
# PAM authentication, then enable this but set PasswordAuthentication | |
# and ChallengeResponseAuthentication to 'no'. | |
UsePAM yes | |
#AllowAgentForwarding yes | |
#AllowTcpForwarding yes | |
#GatewayPorts no | |
X11Forwarding yes | |
#X11DisplayOffset 10 | |
#X11UseLocalhost yes | |
#PermitTTY yes | |
PrintMotd no | |
#PrintLastLog yes | |
#TCPKeepAlive yes | |
#UseLogin no | |
#PermitUserEnvironment no | |
#Compression delayed | |
#ClientAliveInterval 0 | |
#ClientAliveCountMax 3 | |
#UseDNS no | |
#PidFile /var/run/sshd.pid | |
#MaxStartups 10:30:100 | |
#PermitTunnel no | |
#ChrootDirectory none | |
#VersionAddendum none | |
# no default banner path | |
#Banner none | |
# Allow client to pass locale environment variables | |
AcceptEnv LANG LC_* | |
# override default of no subsystems | |
Subsystem sftp /usr/lib/openssh/sftp-server -f AUTHPRIV -l INFO | |
# Example of overriding settings on a per-user basis | |
#Match User anoncvs | |
# X11Forwarding no | |
# AllowTcpForwarding no | |
# PermitTTY no | |
# ForceCommand cvs server |
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You need to generate the
ssh_host_ed25519_key
andssh_host_rsa_key
files in/etc/ssh/
directory and to delete the remainingssh_host_*key*
files containing the weak cyphers.The /etc/ssh/moduli file contains prime numbers and generators used by the SSH server for the Diffie-Hellman key exchange. Your current /etc/ssh/moduli is probably not unique. Generating a new file may harden your server. Generating these file might take awhile.
After all these changes, it is possible to not be able to connect to the server with your private key, if it is not strong enough. So you might need to generate a new one with
ssh-keygen -t rsa -b 4096
.