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openssh-server: harden sshd config

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Harden sshd configuration by adding KexAlgorithms, Ciphers and MACs for sshd,
following good pratices on https://infosec.mozilla.org/guidelines/openssh

Change-Id: I3051320d867a5033e82deef10c5e723ca9829884
Co-Authored-By: Nicolas Hicher <nhicher@redhat.com>
This commit is contained in:
Tristan Cacqueray 2019-04-19 00:57:10 +00:00 committed by Nicolas Hicher
parent b9e322f2d3
commit 11ec95b779
3 changed files with 41 additions and 0 deletions
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4
diskimage_builder/elements/openssh-server/README.rst
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@ -3,6 +3,10 @@ openssh-server
==============
This element ensures that openssh server is installed and enabled during boot.
To disable hardening of sshd configuration, you have to set
``DIB_OPENSSH_SERVER_HARDENING`` to 0. This option will configure KexAlgorithms,
Ciphers and MAC following good pratices on
https://infosec.mozilla.org/guidelines/openssh
Note
----

30
diskimage_builder/elements/openssh-server/post-install.d/99-harden-sshd-config Executable file
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@ -0,0 +1,30 @@
#!/bin/bash
if [ ${DIB_DEBUG_TRACE:-1} -gt 0 ]; then
set -x
fi
set -eu
set -o pipefail
if [ ${DIB_OPENSSH_SERVER_HARDENING:-1} -eq 1 ]; then
macs="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"
ciphers="Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr"
kexalgorithms="KexAlgorithms curve25519-sha256@libssh.org,ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256"
if ! grep -qE "^MACs" /etc/ssh/sshd_config; then
sed -i "/# Ciphers and keying/a $macs" /etc/ssh/sshd_config
elif ! grep -qE "$macs" /etc/ssh/sshd_config; then
sed -i "s/^MACs.*/$macs/" /etc/ssh/sshd_config
fi
if ! grep -qE "^Ciphers" /etc/ssh/sshd_config; then
sed -i "/# Ciphers and keying/a $ciphers" /etc/ssh/sshd_config
elif ! grep -qE "$ciphers" /etc/ssh/sshd_config; then
sed -i "s/^Ciphers.*/$ciphers/" /etc/ssh/sshd_config
fi
if ! grep -qE "^KexAlgorithms" /etc/ssh/sshd_config; then
sed -i "/# Ciphers and keying/a $kexalgorithms" /etc/ssh/sshd_config
elif ! grep -qE "$kexalgorithms" /etc/ssh/sshd_config; then
sed -i "s/^KexAlgorithms.*/$kexalgorithms/" /etc/ssh/sshd_config
fi
fi

7
releasenotes/notes/harden-sshd-config-3f84556136014f95.yaml Normal file
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@ -0,0 +1,7 @@
---
security:
- a new post-install script was added in openssh-server element to ensure
KexAlgorithms, Ciphers and MACs for sshd_config will be configured following
good pratices on https://infosec.mozilla.org/guidelines/openssh. This option
is activated by default, users can set DIB_OPENSSH_SERVER_HARDENING to 0 to
disable this sshd configuration