ref:https://www.seebug.org/vuldb/ssvid-96217
简要描述：
为准备乌云深圳沙龙，准备几个0day做案例。 官方承认这个问题，说明会发布补丁，但不愿承认这是个『漏洞』……不过也无所谓，反正是不是都没美刀~
详细说明：
CI在加载模板的时候，会调用 $this->load->view('template_name', $data); 内核中，查看view函数源码： /system/core/Loader.php
public function view($view, $vars = array(), $return = FALSE)
{
return $this->_ci_load(array('_ci_view' => $view, '_ci_vars' => $this->_ci_object_to_array($vars), '_ci_return' => $return));
}
...
protected function _ci_load($_ci_data)
{
// Set the default data variables
foreach (array('_ci_view', '_ci_vars', '_ci_path', '_ci_return') as $_ci_val)
{
$$_ci_val = isset($_ci_data[$_ci_val]) ? $_ci_data[$_ci_val] : FALSE;
}
$file_exists = FALSE;
// Set the path to the requested file
if (is_string($_ci_path) && $_ci_path !== '')
{
$_ci_x = explode('/', $_ci_path);
$_ci_file = end($_ci_x);
}
else
{
$_ci_ext = pathinfo($_ci_view, PATHINFO_EXTENSION);
$_ci_file = ($_ci_ext === '') ? $_ci_view.'.php' : $_ci_view;
foreach ($this->_ci_view_paths as $_ci_view_file => $cascade)
{
if (file_exists($_ci_view_file.$_ci_file))
{
$_ci_path = $_ci_view_file.$_ci_file;
$file_exists = TRUE;
break;
}
if ( ! $cascade)
{
break;
}
}
}
if ( ! $file_exists && ! file_exists($_ci_path))
{
show_error('Unable to load the requested file: '.$_ci_file);
}
// This allows anything loaded using $this->load (views, files, etc.)
// to become accessible from within the Controller and Model functions.
$_ci_CI =& get_instance();
foreach (get_object_vars($_ci_CI) as $_ci_key => $_ci_var)
{
if ( ! isset($this->$_ci_key))
{
$this->$_ci_key =& $_ci_CI->$_ci_key;
}
}
/*
* Extract and cache variables
*
* You can either set variables using the dedicated $this->load->vars()
* function or via the second parameter of this function. We'll merge
* the two types and cache them so that views that are embedded within
* other views can have access to these variables.
*/
if (is_array($_ci_vars))
{
$this->_ci_cached_vars = array_merge($this->_ci_cached_vars, $_ci_vars);
}
extract($this->_ci_cached_vars);
/*
* Buffer the output
*
* We buffer the output for two reasons:
* 1. Speed. You get a significant speed boost.
* 2. So that the final rendered template can be post-processed by
* the output class. Why do we need post processing? For one thing,
* in order to show the elapsed page load time. Unless we can
* intercept the content right before it's sent to the browser and
* then stop the timer it won't be accurate.
*/
ob_start();
// If the PHP installation does not support short tags we'll
// do a little string replacement, changing the short tags
// to standard PHP echo statements.
if ( ! is_php('5.4') && ! ini_get('short_open_tag') && config_item('rewrite_short_tags') === TRUE)
{
echo eval('?>'.preg_replace('/;*s*?>/', '; ?>', str_replace('<?=', '<?php echo ', file_get_contents($_ci_path))));
}
else
{
include($_ci_path); // include() vs include_once() allows for multiple views with the same name
}
log_message('info', 'File loaded: '.$_ci_path);
// Return the file data if requested
if ($_ci_return === TRUE)
{
$buffer = ob_get_contents();
[@ob_end_clean](/ob_end_clean)();
return $buffer;
}
/*
* Flush the buffer... or buff the flusher?
*
* In order to permit views to be nested within
* other views, we need to flush the content back out whenever
* we are beyond the first level of output buffering so that
* it can be seen and included properly by the first included
* template and any subsequent ones. Oy!
*/
if (ob_get_level() > $this->_ci_ob_level + 1)
{
ob_end_flush();
}
else
{
$_ci_CI->output->append_output(ob_get_contents());
[@ob_end_clean](/ob_end_clean)();
}
return $this;
}
且看这一段：
if (is_array($_ci_vars))
{
$this->_ci_cached_vars = array_merge($this->_ci_cached_vars, $_ci_vars);
}
extract($this->_ci_cached_vars);
这个extract将导致变量覆盖漏洞。 $this->_ci_cached_vars是来自$_ci_vars，而$_ci_vars是来自用户传给view方法的第二个参数。（正常情况下是开发者传给模板的变量） 而我们看到extract后面：
extract($this->_ci_cached_vars);
ob_start();
// If the PHP installation does not support short tags we'll
// do a little string replacement, changing the short tags
// to standard PHP echo statements.
if ( ! is_php('5.4') && ! ini_get('short_open_tag') && config_item('rewrite_short_tags') === TRUE)
{
echo eval('?>'.preg_replace('/;*s*?>/', '; ?>', str_replace('<?=', '<?php echo ', file_get_contents($_ci_path))));
}
else
{
include($_ci_path); // include() vs include_once() allows for multiple views with the same name
}
include($_ci_path)，$_ci_path是模板地址，因为之前的变量覆盖，将会导致任意文件包含漏洞，进而getshell。 所以，只要我们可以控制view的第二个参数的『键值』，传入 _ci_path=file:///etc/passwd ，在被extract后覆盖原来的模板地址，将可以包含/etc/passwd。 这个漏洞和 http://**.**.**.**/bugs/wooyun-2014-051906 有点类似，就是在assign（CI里叫$this->load->vars或是$this->load->view）的时候传入数组导致的。
漏洞证明：
如下Controller将可导致漏洞：
<?php
defined('BASEPATH') OR exit('No direct script access allowed');
class Welcome extends CI_Controller {
public function index()
{
$data = $this->input->post();
$this->load->view('welcome_message', $data);
}
}
这个也类似：
public function index()
{
$data = $this->input->post('info');
$this->load->vars($data);
$this->load->view('welcome_message');
}
当开启了远程文件包含的情况下，也可以直接包含php://input
