Linux: SSH AllowTcpForwarding

# SPDX-FileCopyrightText: 2020 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

if(description)
{
  script_oid("1.3.6.1.4.1.25623.1.0.150228");
  script_version("2023-07-27T05:05:09+0000");
  script_tag(name:"last_modification", value:"2023-07-27 05:05:09 +0000 (Thu, 27 Jul 2023)");
  script_tag(name:"creation_date", value:"2020-05-07 06:49:26 +0000 (Thu, 07 May 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 AllowTcpForwarding");

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

  script_add_preference(name:"Value", type:"radio", value:"no;yes", 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: 5.2.21 Ensure SSH AllowTcpForwarding is disabled (Scored)");
  script_xref(name:"Policy", value:"CIS Controls Version 7: 9.2 Ensure Only Approved Ports Protocols and Services Are Running");

  script_tag(name:"summary", value:"SSH port forwarding is a mechanism in SSH for tunneling application ports
  from the client to the server, or servers to clients. It can be used for adding encryption to
  legacy applications, going through firewalls, and some system administrators and IT professionals
  use it for opening backdoors into the internal network from their home machines. Leaving port
  forwarding enabled can expose the organization to security risks and back-doors.");

  exit(0);
}

include("policy_functions.inc");

cmd = "grep '^AllowTcpForwarding' /etc/ssh/sshd_config";
title = "SSH AllowTcpForwarding";
solution = "Edit the /etc/ssh/sshd_config file to set the parameter as follows:
AllowTcpForwarding no";
test_type = "SSH_Cmd";
default = script_get_preference("Value", id:1);

if(get_kb_item("linux/mount/ERROR")){
  value = "Error";
  compliant = "incomplete";
  comment = "Could not read /etc/ssh/sshd_config";
}else{
  value = get_kb_item("Policy/linux/sshd_config/allowtcpforwarding");
  compliant = policy_setting_exact_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);