Linux: ARP proxy

# 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("1.3.6.1.4.1.25623.1.0.150151");
  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:"2020-03-10 09:36:32 +0000 (Tue, 10 Mar 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: ARP proxy");

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

  script_add_preference(name:"Status", type:"radio", value:"Disabled;Enabled", id:1);

  script_xref(name:"URL", value:"https://linux.die.net/man/5/sysctl.conf");
  script_xref(name:"URL", value:"https://wiki.debian.org/BridgeNetworkConnectionsProxyArp");

  script_tag(name:"summary", value:"This prevents ARP packet attacks from affecting the system.

This script tests whether the Linux host is configured to disable ARP proxy.");

  exit(0);
}

include("policy_functions.inc");

cmd = "sysctl net.ipv4.conf.all.proxy_arp, sysctl net.ipv4.conf.default.proxy_arp";
title = "ARP proxy";
solution = "sysctl -w net.ipv4.conf.all.proxy_arp = [0,1], sysctl -w sysctl net.ipv4.conf.default.proxy_arp = [0,1]";
test_type = "SSH_Cmd";
default = script_get_preference("Status", id:1);

if(get_kb_item("Policy/linux/sysctl/ssh/ERROR")){
  value = "Error";
  compliant = "incomplete";
  comment = "No SSH connection to host";
}else if(get_kb_item("Policy/linux/sysctl/ERROR")){
  value = "Error";
  compliant = "incomplete";
  comment = "Can not run sysctl command";
}else{
  # sysctl -a output
  net_ipv4_conf_all_proxy_arp = get_kb_item("Policy/linux/sysctl/net.ipv4.conf.all.proxy_arp");
  net_ipv4_conf_default_proxy_arp = get_kb_item("Policy/linux/sysctl/net.ipv4.conf.default.proxy_arp");

  if(!net_ipv4_conf_all_proxy_arp || !net_ipv4_conf_default_proxy_arp){
    value = "Error";
    compliant = "incomplete";
    comment = "Could not find setting with sysctl";
  }else{
    if(net_ipv4_conf_all_proxy_arp == "0" && net_ipv4_conf_default_proxy_arp == "0")
      value = "Disabled";
    else
      value = "Enabled";
    compliant = policy_setting_exact_match(value:value, set_point:default);
  }

  if(get_kb_item("Policy/linux/sysctl/conf/ERROR")){
    comment = "No SSH connection to host to read /etc/sysctl config files.";
  }else{
    files = make_list("/etc/sysctl.conf", get_kb_list("Policy/linux//etc/sysctl.d//files/"));
    foreach file (files){
      if(get_kb_item("Policy/linux/" + file + "/content/ERROR"))
        continue;

      content = get_kb_item("Policy/linux/" + file + "/content");

      grep_pattern = egrep(string:content, pattern:"(net.ipv4.conf.all.proxy_arp|net.ipv4.conf.default.proxy_arp)");
      if(grep_pattern){
        grep_pattern = str_replace(string:grep_pattern, find:'\r\n', replace:" ");
        comment += ', ' + file + ": " + chomp(grep_pattern);
      }
    }

    if(comment)
      comment = str_replace(string:comment, find:', ', replace:"", count:1);
    else
      comment = "Could not find setting in any sysctl config file";
  }
}

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);