------------------------------------------------------------------------ WordPress audio playlist functionality is affected by Cross-Site Scripting ------------------------------------------------------------------------ Yorick Koster, July 2016 ------------------------------------------------------------------------ Abstract ------------------------------------------------------------------------ Two Cross-Site Scripting vulnerabilities exists in the playlist functionality of WordPress. These issues can be exploited by convincing an Editor or Administrator into uploading a malicious MP3 file. Once uploaded the issues can be triggered by a Contributor or higher using the playlist shortcode. ------------------------------------------------------------------------ OVE ID ------------------------------------------------------------------------ OVE-20160717-0003 ------------------------------------------------------------------------ Tested versions ------------------------------------------------------------------------ This issue was successfully tested on the WordPress version 4.5.3. ------------------------------------------------------------------------ Fix ------------------------------------------------------------------------ These issues are resolved in WordPress version 4.7.3. ------------------------------------------------------------------------ Details ------------------------------------------------------------------------ https://sumofpwn.nl/advisory/2016/wordpress_audio_playlist_functionality_is_affected_by_cross_site_scripting.html It was discovered that meta information (ID3) stored in audio files are not properly sanitized in case they are uploaded by a user with the unfiltered_html (generally an Editor or Administrator). The first Cross-Site Scripting vulnerability exists in the function that processes the playlist shortcode, which is done in the wp_playlist_shortcode() method (/wp-includes/media.php). This method creates a <noscript> block for users with JavaScript disabled. The method wp_get_attachment_link() does not perform any output encoding on the link text. Meta information from the audio file is used in the link text, rendering wp_playlist_shortcode() vulnerable to Cross-Site Scripting. The second Cross-Site Scripting issue is DOM-based and exists in the JavaScript file /wp-includes/js/mediaelement/wp-playlist.js (or /wp-includes/js/mediaelement/wp-playlist.min.js). The WPPlaylistView object is used to render a audio player client side. The method renderTracks() uses the meta information from the audio file in a call to jQuery's append() method. No output encoding is used on the meta information, resulting in a Cross-Site Scripting vulnerability. Proof of concept The following MP3 file can be used to reproduce this issue: https://securify.nl/advisory/SFY20160742/xss.mp3 1) upload MP3 file to the Media Library (as Editor or Administrator). 2) Insert an Audio Playlist in a Post containing this MP3 (Create Audio Playlist). ------------------------------------------------------------------------ Summer of Pwnage (https://sumofpwn.nl) is a Dutch community project. Its goal is to contribute to the security of popular, widely used OSS projects in a fun and educational way.