debian-cis/bin/hardening/3.2.8_enable_tcp_syn_cookies.sh

#!/bin/bash

#
# CIS Debian Hardening
#

#
# 3.2.8 Ensure TCP SYN Cookies is enabled (Scored)
#

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

HARDENING_LEVEL=2
DESCRIPTION="Enable TCP-SYN cookie to prevent TCP-SYN flood attack."

SYSCTL_PARAMS='net.ipv4.tcp_syncookies=1'

# This function will be called if the script status is on enabled / audit mode
audit () {
    for SYSCTL_VALUES in $SYSCTL_PARAMS; do
        SYSCTL_PARAM=$(echo $SYSCTL_VALUES | cut -d= -f 1)
        SYSCTL_EXP_RESULT=$(echo $SYSCTL_VALUES | cut -d= -f 2)
        debug "$SYSCTL_PARAM should be set to $SYSCTL_EXP_RESULT"
        has_sysctl_param_expected_result $SYSCTL_PARAM $SYSCTL_EXP_RESULT
        if [ $FNRET != 0 ]; then
            crit "$SYSCTL_PARAM was not set to $SYSCTL_EXP_RESULT"
        elif [ $FNRET = 255 ]; then
            warn "$SYSCTL_PARAM does not exist -- Typo?"
        else
            ok "$SYSCTL_PARAM correctly set to $SYSCTL_EXP_RESULT"
        fi
    done
}

# This function will be called if the script status is on enabled mode
apply () {
    for SYSCTL_VALUES in $SYSCTL_PARAMS; do
        SYSCTL_PARAM=$(echo $SYSCTL_VALUES | cut -d= -f 1)
        SYSCTL_EXP_RESULT=$(echo $SYSCTL_VALUES | cut -d= -f 2)
        debug "$SYSCTL_PARAM should be set to $SYSCTL_EXP_RESULT"
        has_sysctl_param_expected_result $SYSCTL_PARAM $SYSCTL_EXP_RESULT
        if [ $FNRET != 0 ]; then
            warn "$SYSCTL_PARAM was not set to $SYSCTL_EXP_RESULT -- Fixing"
            set_sysctl_param $SYSCTL_PARAM $SYSCTL_EXP_RESULT
            sysctl -w net.ipv4.route.flush=1 > /dev/null
        elif [ $FNRET = 255 ]; then
            warn "$SYSCTL_PARAM does not exist -- Typo?"
        else
            ok "$SYSCTL_PARAM correctly set to $SYSCTL_EXP_RESULT"
        fi
    done
}

# This function will check config parameters required
check_config() {
    :
}

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

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