Pierluigi Paganini
May 01, 2020
The developers behind the Ninja Forms WordPress plugin have addressed a Cross-Site Request Forgery (CSRF) vulnerability that could lead to Stored Cross-Site Scripting (Stored XSS) attacks.
Ninja Forms is a drag and drop form builder plugin for WordPress builder that allows users to easily create complex forms within just a few minutes.
The WordPress plugin has currently more than 1 million installs, the flaw affects all Ninja Forms versions up to 3.4.24.2.
The issue, rated as a high severity security flaw (CVSS score of 8.8), could be exploited by attackers to inject malicious code and take over websites.
“On April 27, 2020, the Wordfence Threat Intelligence team discovered a Cross-Site Request Forgery(CSRF) vulnerability in Ninja Forms, a WordPress plugin with over 1 million installations.” reads the post published by WordFence. “This vulnerability could allow an attacker to trick an administrator into importing a contact form containing malicious JavaScript and replace any existing contact form with the malicious version.”
The attack scenario sees hackers tricking WordPress admins into clicking specially crafted links that inject the malicious JavaScript code as part of a newly-imported contact form.
Experts from Wordfence explained that hackers could abuse the plugin’s functionality to replace all existing forms on a targeted website with a malicious one.
The Ninja Forms plugin includes a “legacy” mode which allows users to revert its styling and features to those of the plugin’s final 2.9.x version. It leverages multiple AJAX functions that import forms and fields between the “legacy” mode and the default mode. Experts noticed that two of these functions failed to check nonces, this means that they don’t verify the identity of the user that sent a request.
The ninja_forms_ajax_import_form AJAX function is one of them and the issue allows to spoof requests using an administrator’s session after they click a crafted link and import forms containing malicious JavaScript code.
“As such, if an attacker was able to trick an administrator into clicking a crafted link, they could spoof a request using that administrator’s session and import a form containing malicious JavaScript into the site. Worse yet, it was possible to replace any existing form on the site with one of these imported forms by setting the formID $_POST parameter to the ID of an existing form.” continues the post.
“Depending on where the JavaScript was placed in the imported form, it could be executed in a victim’s browser whenever they visited a page containing the form, whenever an Administrator visited the plugin’s Import/Export page, or whenever an Administrator attempted to edit any of the form’s fields,”
Experts explained that the issue allows hackers to carry out a Cross-Site Scripting (XSS) attack, a malicious script executed in an Administrator’s browser could be used to add new administrative accounts, while a malicious script executed in a visitor’s browser could be used to redirect that visitor to a malicious site.
Below the timeline of the issue:
At the time of writing, over 800,000 WordPress sites are still using vulnerable versions of the plugin.
A few days ago, WordFence also disclosed another issue affecting the Real-Time Find and Replace WordPress plugin.
Unfortunately, the number of attacks attempting to exploit vulnerabilities in WordPress plugins continues to increase.
A few weeks ago researchers at NinTechNet reported an ongoing campaign that was actively exploiting a zero-day flaw in the WordPress Flexible Checkout Fields for WooCommerce plugin. Other attacks recently observed are:
I believe it is very important to protect WordPress install with dedicated solutions, I’m currently using WordFence solution, the company provided with a license to evaluate the premium features.
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