Fraud Blocker Slider Revolution Plugin Update Fixes XSS Vulnerability

XSS Vulnerability Fixed in Slider Revolution Plugin Update


Unauthenticated XSS Vulnerability Patched in Slider Revolution Plugin: A Wake-Up Call for WordPress Security

In the ever-evolving landscape of website security, vulnerabilities are an unfortunate reality. Recently, the popular Slider Revolution plugin, used by over 9 million websites, faced a significant security challenge. An unauthenticated Cross-Site Scripting (XSS) vulnerability was discovered and subsequently patched. This incident serves as a crucial reminder of the importance of robust security measures, especially for WordPress users. At WP-Firewall, we understand the gravity of such vulnerabilities and are committed to providing top-notch security solutions to safeguard your WordPress sites.

Understanding the Vulnerability

– What is XSS?

Cross-Site Scripting (XSS) is a type of security vulnerability typically found in web applications. It allows attackers to inject malicious scripts into web pages viewed by other users. These scripts can steal sensitive information, manipulate web content, or even perform actions on behalf of the user without their consent.

– The Slider Revolution Incident

Slider Revolution, a widely-used WordPress plugin known for its versatility in creating responsive sliders, hero images, and even one-page websites, was found to have an unauthenticated stored XSS vulnerability. This flaw allowed unauthenticated users to exploit the plugin by sending a single HTTP request, leading to potential privilege escalation on the affected WordPress site.

The vulnerability was due to improper sanitization and output escaping of user input in the slider's parameter data. Additionally, a broken access control on one of the plugin's REST API endpoints allowed unauthenticated users to update slider data. By chaining these two conditions, attackers could achieve unauthenticated stored XSS.

The Patch and Its Implications

– Immediate Actions Taken

Upon discovering the vulnerability, the Slider Revolution team acted swiftly. They released version 6.7.0 to address the unauthenticated broken access control issue and version 6.7.11 to fully patch the authenticated stored XSS vulnerability. These updates are crucial for all users of the plugin, and it is highly recommended to update to these versions or higher immediately.

– Technical Breakdown

The primary issue was in the `init_rest_api` function, which registered a REST API endpoint without proper permission checks. The `check_nonce` function, intended to verify nonce values, did not include adequate permission checks, allowing unauthenticated users to fetch nonce values and exploit the vulnerability.

Here is a snippet of the problematic code:

public function init_rest_api(){
register_rest_route('sliderrevolution', '/sliders', array(
'show_in_index' => false,
'callback' => array($this, 'save_slider'),
'permission_callback' => array($this, 'check_nonce'),

public function check_nonce(){
$nonce = $this->get_request_var('nonce');
$nonce = (empty($nonce)) ? $this->get_request_var('rs-nonce') : $nonce;
if(wp_verify_nonce($nonce, 'revslider_actions') == false){
$this->ajax_response_error(__('Bad Request', 'revslider'));
return true;

The `check_nonce` function only checked the nonce value, which could be fetched by an unauthenticated user through the `js_add_header_scripts` function, leading to the exploitation of the vulnerability.

– The Fix

To mitigate this issue, the Slider Revolution team removed the affected REST API endpoint and applied proper sanitization and escaping to the affected slider data or parameters. This approach ensures that user input is sanitized before being stored and escaped before being displayed, preventing malicious scripts from being executed.

Lessons Learned and Best Practices

– Importance of Regular Audits

This incident underscores the importance of regular security audits for WordPress plugins and themes. At WP-Firewall, we offer comprehensive security auditing services to identify and address potential vulnerabilities before they can be exploited.

– Implementing Proper Sanitization and Escaping

Developers must implement proper sanitization and escaping for all user inputs. Depending on the context, functions like `sanitize_text_field`, `esc_html`, and `esc_attr` should be used to ensure that data is safe for display.

– Robust Access Control

Access control mechanisms should be robust and thoroughly tested. Functions that handle sensitive actions or data should include strict permission checks to prevent unauthorized access.

– Staying Updated

Keeping plugins and themes updated is crucial. Developers frequently release patches and updates to address newly discovered vulnerabilities. Users should enable automatic updates or regularly check for updates to ensure their sites are protected.

How WP-Firewall Can Help

At WP-Firewall, we are dedicated to providing comprehensive security solutions for WordPress users. Our services include:

– Real-Time Threat Detection

Our advanced firewall detects and blocks malicious traffic in real-time, ensuring that your site remains secure from potential threats.

– Regular Security Audits

We conduct thorough security audits to identify vulnerabilities in your WordPress installation, plugins, and themes. Our detailed reports provide actionable insights to enhance your site's security.

– Automatic Updates and Patching

Our platform ensures that your WordPress core, plugins, and themes are always up-to-date with the latest security patches. We automate the update process to minimize the risk of vulnerabilities.

– Vulnerability Scanning

Our vulnerability scanning tools continuously monitor your site for potential security issues. We provide immediate alerts and recommendations to address any detected vulnerabilities.

– Expert Support

Our team of security experts is available 24/7 to assist you with any security-related concerns. Whether you need help with a specific issue or general advice on improving your site's security, we are here to help.


The unauthenticated XSS vulnerability in the Slider Revolution plugin is a stark reminder of the importance of robust security measures in the WordPress ecosystem. By staying vigilant, implementing best practices, and leveraging the expertise of security professionals like WP-Firewall, you can protect your site from potential threats.

If you are a Slider Revolution user, update your plugin to version 6.7.11 or higher immediately. For comprehensive WordPress security solutions, consider partnering with WP-Firewall. Together, we can make the internet a safer place.

– Stay Secure with WP-Firewall

Protect your WordPress site with our advanced security solutions. Learn more about WP-Firewall and how we can help you safeguard your online presence.

Join the Conversation

Have thoughts on this topic? Share your insights and experiences in the comments below. Let's work together to enhance WordPress security for everyone.

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By staying proactive and informed, we can collectively enhance the security of the WordPress ecosystem. Thank you for reading, and stay secure!

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