Fortinet FortiOS 5.x < 5.4.2 Flow-mode Detection Bypass

#
# (C) Tenable Network Security, Inc.
#

include("compat.inc");

if (description)
{
  script_id(95439);
  script_version("1.7");
  script_cvs_date("Date: 2019/11/13");

  script_cve_id("CVE-2016-7541");
  script_bugtraq_id(94477);

  script_name(english:"Fortinet FortiOS 5.x < 5.4.2 Flow-mode Detection Bypass");
  script_summary(english:"Checks the version of FortiOS.");

  script_set_attribute(attribute:"synopsis", value:
"The remote host is affected by a security bypass vulnerability.");
  script_set_attribute(attribute:"description", value:
"The remote FortiGate device is running a version of FortiOS that is
5.x prior to 5.4.2. It is, therefore, affected by a security bypass
vulnerability when reloading the scanning engine after an update that
results in active network sessions no longer being monitored by
flow-mode detection. An unauthenticated, remote attacker can exploit
this vulnerability to bypass security protection.");
  # http://fortiguard.com/advisory/fortios-flow-mode-detection-bypass-under-certain-conditions
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?79976042");
  script_set_attribute(attribute:"solution", value:
"Upgrade to Fortinet FortiOS version 5.4.2 or later.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:N/I:P/A:N");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2016-7541");

  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"false");

  script_set_attribute(attribute:"vuln_publication_date", value:"2016/11/22");
  script_set_attribute(attribute:"patch_publication_date", value:"2016/11/22");
  script_set_attribute(attribute:"plugin_publication_date", value:"2016/12/01");

  script_set_attribute(attribute:"potential_vulnerability", value:"true");
  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:fortinet:fortios");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Firewalls");

  script_copyright(english:"This script is Copyright (C) 2016-2019 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("fortinet_version.nbin");
  script_require_keys("Host/Fortigate/model", "Host/Fortigate/version", "Settings/ParanoidReport");

  exit(0);
}

include("audit.inc");
include("global_settings.inc");
include("misc_func.inc");

if (report_paranoia < 2) audit(AUDIT_PARANOID);

app_name = "FortiOS";

version = get_kb_item_or_exit("Host/Fortigate/version");
model = get_kb_item_or_exit("Host/Fortigate/model");

# Make sure device is FortiGate
if (!preg(string:model, pattern:"fortigate", icase:TRUE)) audit(AUDIT_HOST_NOT, "a FortiGate");

if (version =~ "^5\.[024]\.") fix = "5.4.2";
else audit(AUDIT_INST_VER_NOT_VULN, app_name, version);

if (ver_compare(ver:version, fix:fix, strict:FALSE) == -1)
{
  report =
    '\n  Model             : ' + model +
    '\n  Installed version : ' + version +
    '\n  Fixed version     : ' + fix +
    '\n';
  security_report_v4(severity:SECURITY_WARNING, extra:report, port:0);
}
else audit(AUDIT_INST_VER_NOT_VULN, app_name, version);