Configure a Proper Value for MaxAuthTries

# 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("1.3.6.1.4.1.25623.1.0.130488");
  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:"2025-09-25 13:08:37 +0000 (Thu, 25 Sep 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("Configure a Proper Value for MaxAuthTries");

  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/eulerosvirtual");

  script_xref(name:"Policy", value:"EulerOS Virtual: EulerOS Virtual Linux Security Configuration (v1.0.0): 3. Running and Services: 3.2 Firewall: 3.3.14 Configure a Proper Value for MaxAuthTries (Recommendation)");

  script_tag(name:"summary", value:"MaxAuthTries indicates the maximum number of user
authentication failures allowed in a single connection. If the number of user authentication
failures exceeds the value, the connection is automatically disconnected. You are advised to set
this field to a value less than or equal to 3.

If this field is set to a large value, the client can fail to be authenticated for multiple times
in a single connection, reducing the attack cost. If the value is not explicitly configured in the
configuration file, the system uses the default value 6.");

  exit(0);
}

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

title = "Configure a Proper Value for MaxAuthTries";

solution = "Open the /etc/ssh/sshd_config file, set the MaxAuthTries field to the maximum number
of allowed attempts, and restart the sshd service.

# vim /etc/ssh/sshd_config
MaxAuthTries 3
# systemctl restart sshd";

check_type = "SSH_Cmd";

action = 'Run the command in the terminal:
# val=$(awk "/^MaxAuthTries/ {print \\$2}" /etc/ssh/sshd_config); if [ -z "$val" ]; then echo 6; else echo "$val"; fi';

expected_value = 'The output should be less than or equal to "3"';

# ------------------------------------------------------------------
# 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 : MaxAuthTries less than or equal 3
# ------------------------------------------------------------------

step_cmd = 'val=$(awk "/^MaxAuthTries/ {print \\$2}" /etc/ssh/sshd_config); if [ -z "$val" ]; then echo 6; else echo "$val"; fi';
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(int(actual_value) <= int(3)){
  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);