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APPL-26-000140 The macOS system must set SSH Active Server Alive Maximum to 0.

DISA STIG library V1R4
All changes in this version
first version loaded CAT II

Maps to SC-10 via CCI-001133

Title

The macOS system must set SSH Active Server Alive Maximum to 0.

Control

Verify the macOS system is configured to set SSH Active Server Alive Maximum to 0 with the following command: ret="pass" for u in $(/usr/bin/dscl . -list /Users UniqueID | /usr/bin/awk '$2 > 500 {print $1}'); do sshCheck=$(/usr/bin/sudo -u $u /usr/bin/ssh -G . | /usr/bin/grep -c "^serveralivecountmax 0") if [[ "$sshCheck" == "0" ]]; then ret="fail" break fi done /bin/echo $ret If the result is not "pass", this is a finding.

Discussion

SSH must be configured with an Active Server Alive Maximum Count set to 0. Terminating an idle session within a short time reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended. Quickly terminating an idle session or an incomplete login attempt will also free up resources committed by the managed network element. Note: /etc/ssh/ssh_config will be automatically modified to its original state following any update or major upgrade to the operating system.

Related controls

CCI-001133

Fix

Configure the macOS system to set SSH Active Server Alive Maximum to 0 with the following command: include_dir=$(/usr/bin/awk '/^Include/ {print $2}' /etc/ssh/ssh_config | /usr/bin/tr -d '*') ssh_config=("ServerAliveCountMax 0") ssh_setting=$(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