debian-cis/bin/hardening/5.2.18_sshd_limit_access.sh

#!/bin/bash

# run-shellcheck
#
# CIS Debian Hardening
#

#
# 5.2.18 Ensure SSH access is limited (Scored)
#

set -e # One error, it's over
set -u # One variable unset, it's over

# shellcheck disable=2034
HARDENING_LEVEL=3
# shellcheck disable=2034
DESCRIPTION="Limite access via SSH by (dis)allowing specific users or groups."

PACKAGE='openssh-server'
FILE='/etc/ssh/sshd_config'

# This function will be called if the script status is on enabled / audit mode
audit() {
    OPTIONS=("AllowUsers='$ALLOWED_USERS'" "AllowGroups='$ALLOWED_GROUPS'" "DenyUsers='$DENIED_USERS'" "DenyGroups='$DENIED_GROUPS'")
    is_pkg_installed "$PACKAGE"
    if [ "$FNRET" != 0 ]; then
        ok "$PACKAGE is not installed!"
    else
        ok "$PACKAGE is installed"
        for SSH_OPTION in "${OPTIONS[@]}"; do
            SSH_PARAM=$(echo "$SSH_OPTION" | cut -d= -f 1)
            SSH_VALUE=$(echo "$SSH_OPTION" | cut -d= -f 2)
            # shellcheck disable=SC2001
            SSH_VALUE=$(sed "s/'//g" <<<"$SSH_VALUE")
            PATTERN="^${SSH_PARAM}[[:space:]]*$SSH_VALUE"
            does_pattern_exist_in_file_nocase "$FILE" "$PATTERN"
            if [ "$FNRET" = 0 ]; then
                ok "$PATTERN is present in $FILE"
            else
                crit "$PATTERN is not present in $FILE"
            fi
        done
    fi
}

# This function will be called if the script status is on enabled mode
apply() {
    is_pkg_installed "$PACKAGE"
    if [ "$FNRET" = 0 ]; then
        ok "$PACKAGE is installed"
    else
        crit "$PACKAGE is absent, installing it"
        apt_install "$PACKAGE"
    fi
    for SSH_OPTION in "${OPTIONS[@]}"; do
        SSH_PARAM=$(echo "$SSH_OPTION" | cut -d= -f 1)
        SSH_VALUE=$(echo "$SSH_OPTION" | cut -d= -f 2)
        # shellcheck disable=SC2001
        SSH_VALUE=$(sed "s/'//g" <<<"$SSH_VALUE")
        PATTERN="^${SSH_PARAM}[[:space:]]*$SSH_VALUE"
        does_pattern_exist_in_file_nocase "$FILE" "$PATTERN"
        if [ "$FNRET" = 0 ]; then
            ok "$PATTERN is present in $FILE"
        else
            warn "$PATTERN is not present in $FILE, adding it"
            does_pattern_exist_in_file_nocase "$FILE" "^${SSH_PARAM}"
            if [ "$FNRET" != 0 ]; then
                add_end_of_file "$FILE" "$SSH_PARAM $SSH_VALUE"
            else
                info "Parameter $SSH_PARAM is present but with the wrong value -- Fixing"
                replace_in_file "$FILE" "^${SSH_PARAM}[[:space:]]*.*" "$SSH_PARAM $SSH_VALUE"
            fi
            /etc/init.d/ssh reload
        fi
    done
}

# This function will create the config file for this check with default values
create_config() {
    cat <<EOF
status=audit
# Put here ssh user hardening list, there is a default in script to not break your configuration
# However, it can erase current configuration
ALLOWED_USERS=''
ALLOWED_GROUPS=''
DENIED_USERS=''
DENIED_GROUPS=''
EOF
}

# This function will check config parameters required
check_config() {
    if [ -z "$ALLOWED_USERS" ]; then
        info "ALLOWED_USERS is not set, defaults to wildcard"
        ALLOWED_USERS="*"
    fi
    if [ -z "$ALLOWED_GROUPS" ]; then
        info "ALLOWED_GROUPS is not set, defaults to wildcard"
        ALLOWED_GROUPS="*"
    fi
    if [ -z "$DENIED_USERS" ]; then
        info "DENIED_USERS is not set, defaults to nobody"
        DENIED_USERS="nobody"
    fi
    if [ -z "$DENIED_GROUPS" ]; then
        info "DENIED_GROUPS is not set, defaults to nobody"
        DENIED_GROUPS="nobody"
    fi
}

# Source Root Dir Parameter
if [ -r /etc/default/cis-hardening ]; then
    # shellcheck source=../../debian/default
    . /etc/default/cis-hardening
fi
if [ -z "$CIS_LIB_DIR" ]; then
    echo "There is no /etc/default/cis-hardening file nor cis-hardening directory in current environment."
    echo "Cannot source CIS_LIB_DIR variable, aborting."
    exit 128
fi

# Main function, will call the proper functions given the configuration (audit, enabled, disabled)
if [ -r "${CIS_LIB_DIR}"/main.sh ]; then
    # shellcheck source=../../lib/main.sh
    . "${CIS_LIB_DIR}"/main.sh
else
    echo "Cannot find main.sh, have you correctly defined your root directory? Current value is $CIS_LIB_DIR in /etc/default/cis-hardening"
    exit 128
fi