Linux: SSH MaxAuthTries

# Copyright (C) 2020 Greenbone Networks GmbH
#
# SPDX-License-Identifier: GPL-2.0-or-later
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

if(description)
{
  script_oid("1.3.6.1.4.1.25623.1.0.150069");
  script_version("2022-08-31T10:10:28+0000");
  script_tag(name:"last_modification", value:"2022-08-31 10:10:28 +0000 (Wed, 31 Aug 2022)");
  script_tag(name:"creation_date", value:"2020-01-14 14:14:36 +0100 (Tue, 14 Jan 2020)");
  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("Linux: SSH MaxAuthTries");

  script_category(ACT_GATHER_INFO);
  script_copyright("Copyright (C) 2020 Greenbone Networks GmbH");
  script_family("Policy");
  script_dependencies("compliance_tests.nasl", "read_sshd_config.nasl");
  script_mandatory_keys("Compliance/Launch");

  script_add_preference(name:"Value", type:"entry", value:"4", id:1);

  script_xref(name:"URL", value:"https://linux.die.net/man/5/sshd_config");
  script_xref(name:"Policy", value:"CIS Distribution Independent Linux v2.0.0: 5.2.7 Ensure SSH MaxAuthTries is set to 4 or less (Scored)");
  script_xref(name:"Policy", value:"CIS CentOS Linux 8 Benchmark v1.0.0: 5.2.7 Ensure SSH MaxAuthTries is set to 4 or less (Scored)");
  script_xref(name:"Policy", value:"CIS Controls Version 7: 16.13 Alert on Account Login Behavior Deviation");

  script_tag(name:"summary", value:"The MaxAuthTriesparameter specifies the maximum number of authentication
  attempts permitted per connection. When the login failure count reaches half the number, error
  messages will be written to the syslogfile detailing the login failure.

  Setting the MaxAuthTriesparameter to a low number will minimize the risk of successful brute force
  attacks to the SSH server. While the recommended setting is 4, set the number based on site policy.");

  exit(0);
}

include("ssh_func.inc");
include("policy_functions.inc");

cmd = "grep '^MaxAuthTries' /etc/ssh/sshd_config";
title = "SSH MaxAuthTries";
solution = "Edit the /etc/ssh/sshd_config file to set the parameter as follows:
MaxAuthTries 4";
test_type = "SSH_Cmd";
default = script_get_preference("Value", id:1);

if(get_kb_item("Policy/linux/sshd_config/ERROR")){
  value = "Error";
  compliant = "incomplete";
  comment = "Could not read /etc/ssh/sshd_config";
}else{
  value = get_kb_item("Policy/linux/sshd_config/maxauthtries");
  compliant = policy_setting_max_match(value:value, set_point:default);
  comment = "";
}

policy_reporting(result:value, default:default, compliant:compliant, fixtext:solution,
  type:test_type, test:cmd, info:comment);
policy_set_kbs(type:test_type, cmd:cmd, default:default, solution:solution, title:title,
  value:value, compliant:compliant);

exit(0);