Enable TCP-SYN Cookie Protection

# SPDX-FileCopyrightText: 2025 Greenbone AG
# Some text descriptions might be excerpted from (a) referenced
# source(s), and are Copyright (C) by the respective right holder(s).
#
# SPDX-License-Identifier: GPL-2.0-only

# ------------------------------------------------------------------
# METADATA
# ------------------------------------------------------------------

if(description)
{
  script_oid("1.3.6.1.4.1.25623.1.0.130345");
  script_version("2025-11-21T05:40:28+0000");
  script_tag(name:"last_modification", value:"2025-11-21 05:40:28 +0000 (Fri, 21 Nov 2025)");
  script_tag(name:"creation_date", value:"2025-05-07 11:44:20 +0000 (Wed, 07 May 2025)");
  script_tag(name:"cvss_base", value:"0.0");
  script_tag(name:"cvss_base_vector", value:"AV:L/AC:H/Au:S/C:N/I:N/A:N");
  script_tag(name:"qod", value:"97");

  script_name("Enable TCP-SYN Cookie Protection");

  script_category(ACT_GATHER_INFO);
  script_copyright("Copyright (C) 2025 Greenbone AG");
  script_family("Policy");
  script_dependencies("compliance_tests.nasl", "compliance_os_check.nasl");

  script_mandatory_keys("Compliance/Launch", "policy/ssh/login/euleros_eulerosvirtual_openeuler_hce");

  script_xref(name:"Policy", value:"EulerOS Baseline: openEuler Security Configuration Baseline (v1.0.0): 3. Running and Services: 3.5 Kernel: 3.5.14 Enable TCP-SYN Cookie Protection (Requirement)");
  script_xref(name:"Policy", value:"EulerOS Virtual: openEuler Security Configuration Baseline (v1.0.0): 3. Running and Services: 3.5 Kernel: 3.5.14 Enable TCP-SYN Cookie Protection (Requirement)");
  script_xref(name:"Policy", value:"HCE Linux (Huawei Cloud EulerOS): openEuler Security Configuration Baseline (v1.0.0): 3. Running and Services: 3.5 Kernel: 3.5.14 Enable TCP-SYN Cookie Protection (Requirement)");
  script_xref(name:"Policy", value:"openEuler Baseline: openEuler Security Configuration Baseline (v1.0.0): 3. Running and Services: 3.5 Kernel: 3.5.14 Enable TCP-SYN Cookie Protection (Requirement)");

  script_tag(name:"summary", value:"TCP-SYN cookie protection mitigates the impact of SYN flood
attacks on the system.

When an attacker launches a SYN flood attack, the half-open connection queue in the kernel is
quickly exhausted to block valid connections. If SYN cookie is enabled, the system can still accept
valid connections even if DoS attacks occur.");

  exit(0);
}

include("ssh_func.inc");
include("host_details.inc");
include("policy_reporting_module.inc");

title = "Enable TCP-SYN Cookie Protection";

solution = "1. Run the following commands to temporarily enable the protection. After the reboot,
the default values are restored.

# sysctl -w net.ipv4.tcp_syncookies=1
# sysctl -w net.ipv4.route.flush=1

2. Open the /etc/sysctl.conf file, add or modify the following configuration, and run the sysctl -p
/etc/sysctl.conf command to make the configuration take effect permanently.

net.ipv4.tcp_syncookies=1";

check_type = "SSH_Cmd";

action = 'Run the command in the terminal:
# sysctl net.ipv4.tcp_syncookies';

expected_value = 'The output should match the pattern "net.ipv4.tcp_syncookies\\s*=\\s*1"';

# ------------------------------------------------------------------
# CONNECTION CHECK
# ------------------------------------------------------------------

if(!get_kb_item("login/SSH/success") || !sock = ssh_login_or_reuse_connection()){

  report_ssh_error(title: title,
                   solution: solution,
                   action: action,
                   expected_value: expected_value,
                   check_type: check_type);
  exit(0);
}

# ------------------------------------------------------------------
# CHECK : Verify command sysctl net.ipv4.tcp_syncookies
# ------------------------------------------------------------------

step_cmd = 'sysctl net.ipv4.tcp_syncookies';
actual_value = ssh_cmd(socket:sock, cmd:step_cmd, return_errors:TRUE, return_linux_errors_only:TRUE);

if(eregmatch(string: actual_value, pattern:"(No such file or directory|Permission denied|Command not found|Segmentation fault|service not found|is not running|syntax error near unexpected token|syntax error: unexpected end of file)", icase: TRUE)){
  compliant = "incomplete";
  comment = "Something went wrong during the audit check. Please try again.";
}else if(actual_value =~ 'net.ipv4.tcp_syncookies\\s*=\\s*1'){
  compliant = "yes";
  comment = "Check passed";
}else{
  compliant = "no";
  comment = "Check failed";
}

# ------------------------------------------------------------------
# REPORT
# ------------------------------------------------------------------

target = get_kb_item("policy/ssh/login/os-release");
comment = "Target: " + target + "\n" + comment;

report_audit(action: action,
             actual_value: actual_value,
             expected_value: expected_value,
             is_compliant: compliant,
             solution: solution,
             check_type: check_type,
             title: title,
             comment: comment);

exit(0);