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os_ssh_server_alive_interval_configure Configure SSH ServerAliveInterval option set to $ODV

NIST macOS Security Compliance Project Sequoia Guidance, Revision 4.0 (be5491f)
All changes in this version
first version loaded macOS

Title

Configure SSH ServerAliveInterval option set to $ODV

Control

ret="pass"
for u in $(/usr/bin/dscl . -list /Users UniqueID | /usr/bin/awk '$2 > 500 {print $1}'); do
sshCheck=$(/usr/bin/sudo -u $u /usr/bin/ssh -G . | /usr/bin/grep -c "^serveraliveinterval $ODV")
if [[ "$sshCheck" == "0" ]]; then
ret="fail"
break
fi
done
/bin/echo $ret

Discussion

SSH _MUST_ be configured with an Active Server Alive Maximum Count set to $ODV.

Setting the Active Server Alive Maximum Count to $ODV will log users out after a $ODV seconds interval of inactivity.

NOTE: /etc/ssh/ssh_config will be automatically modified to its original state following any update or major upgrade to the operating system.

NOTE: On macOS 15.2 and higher the SSH configuration can be reset to the macOS default by running /usr/libexec/reset-ssh-configuration.

Related controls

ac-12, sc-10

Fix

[source,bash]
----
include_dir=$(/usr/bin/awk '/^Include/ {print $2}' /etc/ssh/ssh_config | /usr/bin/tr -d '*')

ssh_config_string=("ServerAliveInterval $ODV")
for ssh_config in $ssh_config_string; do
ssh_setting=$(echo $ssh_config | /usr/bin/cut -d " " -f1)
/usr/bin/grep -qEi "^$ssh_setting" "${include_dir}01-mscp-ssh.conf" && /usr/bin/sed -i "" "s/^$ssh_setting.*/${ssh_config}/" "${include_dir}01-mscp-ssh.conf" || echo "$ssh_config" >> "${include_dir}01-mscp-ssh.conf"
for u in $(/usr/bin/dscl . list /users shell | /usr/bin/egrep -v '(^_)|(root)|(/usr/bin/false)' | /usr/bin/awk '{print $1}'); do
config=$(/usr/bin/sudo -u $u /usr/bin/ssh -Gv . 2>&1)
configfiles=$(echo "$config" | /usr/bin/awk '/Reading configuration data/ {print $NF}'| /usr/bin/tr -d '\r')
configarray=( ${(f)configfiles} )
if ! echo $config | /usr/bin/grep -q -i "$ssh_config" ; then
for c in $configarray; do
if [[ "$c" == "/etc/ssh/crypto.conf" ]]; then
continue
fi

/usr/bin/sudo -u $u /usr/bin/grep -qEi "^$ssh_setting" "$c" && /usr/bin/sed -i "" "s/^$ssh_setting.*/${ssh_config}/I" "$c"
if [[ "$c" =~ ".ssh/config" ]]; then
if /usr/bin/grep -qEi "$ssh_setting" "$c" 2> /dev/null; then
old_file=$(cat ~$u/.ssh/config)
echo "$ssh_config" > ~$u/.ssh/config
echo "$old_file" >> ~$u/.ssh/config
fi
fi
done
fi
done
done
----