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 one of those vulnerabilities, a PHP object injection vulnerability being introduced in to the plugin ELEX HelpDesk & Customer Support Ticket System. While looking into the source of that, we found that the underlying source of the vulnerability was a library from Zendesk, a multi-billion dollar company, and that vulnerability was publicly reported to them 10 months ago, but hasn’t been resolved.

Also, notably, the file containing the vulnerability is a sample file, which is something that shouldn’t be shipping in production software, but we often find that those are not removed from libraries being included in WordPress plugins. That isn’t helped by libraries not providing a paired down version intended for production use.

We now are also running all the plugins used by customers through that monitoring 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.

We tested and confirmed that our new firewall plugin for WordPress protected against exploitation of this vulnerability, even before we discovered the vulnerability, as part of its protection against zero-day vulnerabilities.

PHP Object Injection

The automated portion of our proactive monitoring flagged this line of code as possibly leading to a vulnerability:

$params = unserialize(base64_decode($_GET['state']));

That would pass user input through the unserialize() function, which would allow PHP object injection to occur. Whether there is a vulnerability would depend on how that can be accessed.

Looking at the code that runs before it in the file /vendor/zendesk/zendesk_api_client_php/samples/auth/oauth.php in the plugin, it turns out that the code would be accessible to anyone.

Based on the path of the file, it looked that might have come from a third-party library shipped with the plugin. We found it comes from the Zendesk PHP API Client Library and the vulnerable code exists in the current version of the library. We also found that the developer was publicly notified of the vulnerable code through an issue filed by Johan Lindahl on the library’s GitHub project on March 26, 2021. No response has been made to that and the issue hasn’t been resolved.

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.

Concerned About The Security of the Plugins You Use?