[waraxe-2018-SA#107] - Reflected XSS in FV Flowplayer Wordpress plugin
================================================================================

Author: Janek Vind "waraxe"
Date: 20. September 2018
Location: Estonia, Tartu
Web: http://www.waraxe.us/advisory-107.html

Target description:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

FV Player is a free, easy-to-use, and complete solution for embedding FLV or MP4
videos into your posts or pages. With MP4 videos, FV Player offers 98% coverage
even on mobile devices.

https://wordpress.org/plugins/fv-wordpress-flowplayer/
https://foliovision.com/player

Vulnerable version: 7.2.0.727
Fixed version: 7.2.1.727
Active installations: 40 000+

###############################################################################
Reflected XSS in "models/flowplayer.php"
###############################################################################

Reason:
  * Insufficient sanitization of user-supplied data
Attack vector:
  * User-supplied GET parameter "fv_player_preview"
Preconditions:
  * Must be logged in as user with "manage_options" privileges (usually admin)


PHP script "models/flowplayer.php" line 2012:
------------------------[ source code start ]----------------------------------
 <?php if( isset($_GET['fv_player_preview']) && !empty($_GET['fv_player_preview']) ) :
    
    if( !is_user_logged_in() || !current_user_can('manage_options') ){
      ?><script>window.parent.jQuery(window.parent.document).trigger('fvp-preview-complete');</script><?php
      wp_die('Please log in.');
    }
    $shortcode = base64_decode($_GET['fv_player_preview']);
..
        if(preg_match('/src="[^"][^"]*"/i',$shortcode)) {
..
          echo do_shortcode($shortcode);          
------------------------[ source code end ]------------------------------------

We can see that vulnerable PHP script expects user-supplied GET parameter "fv_player_preview"
to be as base64 encoded string. This parameter goes through base64 decoding and resulting
text string is used for output without additional checking or sanitization. As result
we have Reflected XSS vulnerability.

Testing:

For successful testing log in as Wordpress admin or other user with "manage_options"
privileges and then open following URL in web browser:

http://localhost/wp498/?fv_player_embed=1&fv_player_preview=c3JjPSJ3YXJheGUiPHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4

Javascript alert with "XSS" message pops up confirming Reflected XSS vulnerability.

"c3JjPSJ3YXJheGUiPHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4" string in URL is base64
encoded version of the string "src="waraxe"<script>alert('XSS')</script>" with
trailing "=" removed, because PHP function "base64_decode()" does not care about it.

By the way, this Reflected XSS vulnerability allows bypassing anti-XSS filters in
all modern web browsers thanks to base64 encoding.


Disclosure timeline:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
19.09.2018 -> First email sent to developers
19.09.2018 -> Got first response email from developers
19.09.2018 -> Sending detailed information to developers
20.09.2018 -> Found problems are fixed, new version available
20.09.2018 -> Waraxe advisory released
 
Contact:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
come2waraxe@yahoo.com
Janek Vind "waraxe"
 
Waraxe forum:  http://www.waraxe.us/
Personal homepage: http://www.janekvind.com/