Reviewed-by: Michael Tremer michael.tremer@ipfire.org

On 20 Jan 2020, at 20:05, Peter Müller peter.mueller@ipfire.org wrote:

Signed-off-by: Peter Müller peter.mueller@ipfire.org

config/ssh/ssh_config | 27 +++++++++++++-------------- 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/config/ssh/ssh_config b/config/ssh/ssh_config index 2abfae6d1..2e2ee60c3 100644 --- a/config/ssh/ssh_config +++ b/config/ssh/ssh_config @@ -1,33 +1,32 @@ -# OpenSSH client configuration +# OpenSSH client configuration file for IPFire # -# set some basic hardening options for all connections +# The full documentation is available at: https://man.openbsd.org/ssh_config +#

+# Set some basic hardening options for all connections Host *

•    # disable Roaming as it is known to be vulnerable
  

•    # Disable Roaming as it is known to be vulnerable
    UseRoaming no
  
  

•    # only use secure crypto algorithm
  

•    # Only use secure crypto algorithms
    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
  
  

•    # always visualise server host keys (has no technical
  

•    # effect, but helps to identify key based MITM attacks)
  

•    # Always visualise server host keys (but helps to identify key based MITM attacks)
    VisualHostKey yes
  
  

•    # use SSHFP (might work on some up-to-date networks) to look up host keys
  

•    # Use SSHFP (might work on some up-to-date networks) to look up host keys
    VerifyHostKeyDNS yes
  
    # send keep-alive messages to connected server to avoid broken connections
    ServerAliveInterval 10
    ServerAliveCountMax 6
  
  

•    # disable X11 forwarding (security risk)
  

•    ForwardX11 no
  

•    # always check server IP address
  

•    CheckHostIP yes
  

•    # ensure only allowed authentication methods are used
  

•    # Ensure only allowed authentication methods are used
    PreferredAuthentications publickey,keyboard-interactive,password
  
  

• # Prevent information leak by hashing ~/.ssh/known_hosts

• HashKnownHosts yes

# EOF

2.16.4

Hello Michael,

thanks for your reply.

Since the Unbound configuration patch (https://patchwork.ipfire.org/patch/2710/) is based on the same motivation than this one, I am a bit surprised by your Reviewed-by tag on it. :-)

Breaking productive environment is a latter weak point to me, as keeping configuration statements/directives removed in the upstream may or may not cause the same effect. Worse, there may be good reasons for changing upstream defaults which we should track closely due to security considerations. On the other hands, relying on third parties is a bad idea when it comes to security - not to mention personal aversions against relying something or someone in general...

In the end, I figure it is less worse to have a shorter configuration which takes less disk space and is easier to review and audit. You are right, the downside of this is to rely on other people's opinion of security and interoperability.

Thanks, and best regards, Peter Müller

Hello,

I am not 100% sure if I like this change.

Simply because of defaults changing in software. Although we generally want to follow upstream this might break installations.

Do we not see this as a danger?

I would prefer to have shorter configurations, but not breaking production is more important.

-Michael

...

On 20 Jan 2020, at 20:04, Peter Müller peter.mueller@ipfire.org wrote:

In order to keep configurations as small as possible and to make them easier to read/audit, this patch omits all default configuration in the OpenSSH server configuration file.

Further, it mentions where to refer for the full documentation.

Signed-off-by: Peter Müller peter.mueller@ipfire.org

config/ssh/sshd_config | 62 ++++++++++++++++---------------------------------- 1 file changed, 20 insertions(+), 42 deletions(-)

diff --git a/config/ssh/sshd_config b/config/ssh/sshd_config index a248c4906..bea5cee53 100644 --- a/config/ssh/sshd_config +++ b/config/ssh/sshd_config @@ -1,81 +1,59 @@ -# ultra-secure OpenSSH server configuration +# OpenSSH server configuration file for IPFire +# +# The full documentation is available at: https://man.openbsd.org/sshd_config +#

-# only allow version 2 of SSH protocol +# Only allow version 2 of SSH protocol Protocol 2

-# listen on port 22 by default +# Listen on port 22 by default Port 22

-# listen on these interfaces and protocols -AddressFamily any +# Listen on every interface and IPv4 only +AddressFamily inet ListenAddress 0.0.0.0

-# limit authentication thresholds +# Limit authentication timeout to 30 seconds LoginGraceTime 30s -MaxAuthTries 6

-# limit maximum instanctes to prevent DoS +# Limit maximum instanctes to prevent DoS MaxStartups 5

-# ensure proper logging -SyslogFacility AUTH -LogLevel INFO

-# enforce permission checks before a login is accepted -# (prevents damage because of hacked systems with world-writeable -# home directories or similar) -StrictModes yes

-# only allow safe crypto algorithms (may break some _very_ outdated clients) -# see also: https://stribika.github.io/2015/01/04/secure-secure-shell.html +# Only allow safe crypto algorithms (may break some _very_ outdated clients) +# See also: https://stribika.github.io/2015/01/04/secure-secure-shell.html 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

-# enable data compression after successful login only -Compression delayed

-# only allow cryptographically safe SSH host keys (adjust paths if needed) +# Only allow cryptographically safe SSH host keys (adjust paths if needed) HostKey /etc/ssh/ssh_host_ed25519_key HostKey /etc/ssh/ssh_host_ecdsa_key HostKey /etc/ssh/ssh_host_rsa_key

-# only allow login via public key by default +# Only allow login via public key by default PubkeyAuthentication yes PasswordAuthentication no ChallengeResponseAuthentication no -PermitEmptyPasswords no

-# permit root login as there is no other user in IPFire 2.x +# Permit root login as there is no other user in IPFire 2.x PermitRootLogin yes

-# ignore user ~/.rhost* files -IgnoreRhosts yes

-# ignore user known hosts file +# Ignore user ~/.ssh/known_hosts file IgnoreUserKnownHosts yes

-# ignore user environments -PermitUserEnvironment no

-# do not allow any kind of forwarding (provides only low security) +# Do not allow any kind of forwarding (provides only low security); # some of them might need to be re-enabled if SSH server is a jump platform -X11Forwarding no AllowTcpForwarding no AllowAgentForwarding no -PermitTunnel no -GatewayPorts no PermitOpen none

-# detect broken sessions by sending keep-alive messages to -# clients (both via TCP and SSH) -TCPKeepAlive yes +# Detect broken sessions by sending keep-alive messages to clients via SSH connection ClientAliveInterval 10

-# close unresponsive SSH sessions which fail to answer keep-alive +# Close unresponsive SSH sessions which fail to answer keep-alive ClientAliveCountMax 6

-# add support for SFTP +# Add support for SFTP Subsystem sftp /usr/lib/openssh/sftp-server

# EOF

2.16.4