Our Proactive Monitoring Caught a Restricted File Upload Vulnerability Being Introduced in to a WordPress Plugin

One way we help to improve the security of WordPress plugins, not just for our customers of our service, but for everyone using them, is our proactive monitoring of changes made to plugins in the Plugin Directory to try to catch serious vulnerabilities. Through that, we caught a variant of those vulnerabilities, a restricted file upload vulnerability being introduced in to the plugin Sitemap by click5.

We now are also running all the plugins used by customers through that on a weekly basis to provide additional protection for our customers.

The possibility of this vulnerability is also flagged by our Plugin Security Checker, so you can check plugins you use to see if they might have similar issues with that tool.

Restricted File Upload

In the latest version of the plugin, the following code was added to the plugin’s main file, /sitemap-by-click5.php:

if(isset($_POST['update_txt'])){ 
 
  $robots_txt = ABSPATH.'/robots.txt';
  $input = $_POST['file_text']; 
  file_put_contents($robots_txt, $input);
}

That will write data sent with the POST input “file_text” to the robots.txt file in the root directory of the WordPress install. There are no security restrictions on who can access that functionality or what they can write to it.

This could be exploited to do various things, including making changes to the instructions provided by the robots.txt file to search engines, as well as being used alongside a local file inclusion (LFI) vulnerability to cause arbitrary code to be run on the website.

Right below that in the file, additional code was added that allows other changes without any security checks.

WordPress Causes Full Disclosure

As a protest of the moderators of the WordPress Support Forum’s continued inappropriate behavior we changed from reasonably disclosing to full disclosing vulnerabilities for plugins in the WordPress Plugin Directory in protest, until WordPress gets that situation cleaned up, so we are releasing this post and then leaving a message about that for the developer through the WordPress Support Forum. (For plugins that are also in the ClassicPress Plugin Directory, we will follow our reasonable disclosure policy.)

You can notify the developer of this issue on the forum as well.

Hopefully, the moderators will finally see the light and clean up their act soon, so these full disclosures will no longer be needed (we hope they end soon). You would think they would have already done that, but considering that they believe that having plugins, which have millions installs, remain in the Plugin Directory despite them knowing they are vulnerable is “appropriate action”, something is very amiss with them (which is even more reason the moderation needs to be cleaned up).

If the moderation is cleaned up, it would also allow the possibility of being able to use the forum to start discussing fixing the problems caused by the very problematic handling of security by the team running the Plugin Directory, discussions which they have for years shut down through their control of the Support Forum.

Update: To clear up the confusion where developers claim we hadn’t tried to notify them through the Support Forum (while at the same time moderators are complaining about us doing just that), here is the message we left for this vulnerability:

Is It Fixed?

If you are reading this post down the road the best way to find out if this vulnerability or other WordPress plugin vulnerabilities in plugins you use have been fixed is to sign up for our service, since what we uniquely do when it comes to that type of data is to test to see if vulnerabilities have really been fixed. Relying on the developer’s information can lead you astray, as we often find that they believe they have fixed vulnerabilities, but have failed to do that.

Proof of Concept

The following proof of concept will change the contents of the robots.txt in the root of the WordPress install to “Proof of Concept”.

Replace “[path to WordPress]” with the location of WordPress.

<html>
<body>
<form action="http://[path to WordPress]" method="POST">
<input type="hidden" name="update_txt" value="Proof of Concept" />
<input type="hidden" name="file_text" value="Proof of Concept" />
<input type="submit" value="Submit" />
</form>
</body>

Concerned About The Security of the Plugins You Use?

When you are a paying customer of our service, you can suggest/vote for the WordPress plugins you use to receive a security review from us. You can start using the service for free when you sign up now. We also offer security reviews of WordPress plugins as a separate service.

Plugin Vulnerabilities

A service to protect your site against vulnerabilities in WordPress plugins.