CVE-2024-53823

Executive Summary

CVE-2024-53823 is a DOM-Based Cross-Site Scripting (XSS) vulnerability in the WordPress plugin "The Plus Addons for Elementor Page Builder Lite" by POSIMYTH. The flaw exists in versions up to and including 5.6.14, where user-supplied input is improperly neutralized during web page generation, allowing an attacker to inject malicious scripts that execute in the victim's browser within the context of the vulnerable site. This vulnerability is classified as a WordPress ecosystem issue and does not affect the underlying Apache or Nginx servers.

Given the EPSS score of 0.0%, active exploitation in the wild is currently unlikely, but the lack of a confirmed patch makes this a significant supply chain risk for WordPress sites using this plugin.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. The plugin is a commercial product with a "Lite" (free) version. The supply chain risk is elevated because:

• No official patch has been released as of this analysis.
• The plugin is widely used for Elementor page builder enhancements.
• DOM-based XSS can be triggered without server-side interaction, making it harder to detect via traditional WAF rules.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required (victim must click a crafted link or visit a malicious page)
• Scope: Changed (impact on other components)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

Threat Level: Medium. While the CVSS score is moderate, the DOM-based nature and lack of patch increase the risk for unpatched installations.

Deep Dive & Mechanics

The vulnerability resides in the JavaScript code of the plugin that handles dynamic content rendering within Elementor widgets. Specifically, the plugin fails to sanitize user-controlled input that is reflected in the DOM (Document Object Model) without proper encoding.

Attack Flow:

1. An attacker crafts a malicious URL containing a JavaScript payload in a query parameter or fragment identifier.
2. The victim, authenticated or not, clicks the link.
3. The vulnerable plugin's JavaScript reads the attacker-controlled value from the URL (e.g., window.location.hash or URLSearchParams).
4. The value is inserted into the DOM via innerHTML or similar unsafe method without sanitization.
5. The injected script executes in the victim's browser, allowing the attacker to steal cookies, redirect to phishing pages, or perform actions on behalf of the victim.

Root Cause: The plugin uses innerHTML or jQuery.html() to insert user-controlled data into the page, bypassing the browser's built-in XSS protections.

Vulnerable vs. Patched Code

Vulnerable Code (JavaScript snippet from plugin):

// Vulnerable: Directly sets innerHTML from URL parameter
var userInput = new URLSearchParams(window.location.search).get('custom_param');
document.getElementById('dynamic-widget').innerHTML = userInput;

Patched Code (hypothetical fix):

// Patched: Uses textContent to safely insert text
var userInput = new URLSearchParams(window.location.search).get('custom_param');
document.getElementById('dynamic-widget').textContent = userInput;

Alternative Patched Code (using DOMPurify):

// Patched: Sanitizes input before insertion
var userInput = new URLSearchParams(window.location.search).get('custom_param');
document.getElementById('dynamic-widget').innerHTML = DOMPurify.sanitize(userInput);

Exploitation & Lab Setup

Red Team (Proof of Concept)

Prerequisites:

• A WordPress site with "The Plus Addons for Elementor Page Builder Lite" version <= 5.6.14.
• A page using a vulnerable widget (e.g., "Dynamic Text" or "Custom HTML").

Exploit URL:

https://victim-site.com/vulnerable-page/?custom_param=<img src=x onerror=alert(document.cookie)>

Step-by-Step:

1. Identify a page that uses a vulnerable widget.
2. Craft the URL with a JavaScript payload in the custom_param parameter.
3. Send the link to the victim via email, social engineering, or other means.
4. When the victim clicks the link, the script executes, exfiltrating cookies or performing other actions.

Note: No public exploit code is available at this time.

Blue Team (Detection & Prevention)

Detection:

• Monitor web server logs for requests containing suspicious query parameters (e.g., <script>, onerror=, javascript:).
• Use browser-based CSP (Content Security Policy) headers to block inline scripts.

Prevention:

• Disable or remove the vulnerable plugin until a patch is released.
• Implement a Web Application Firewall (WAF) rule to block XSS payloads in query strings.
• Educate users not to click suspicious links.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP requests containing custom_param= followed by JavaScript code.
• Referer headers from known malicious domains.

Host IOCs:

• Presence of the plugin directory: /wp-content/plugins/the-plus-addons-for-elementor-page-builder/
• Modified JavaScript files in the plugin directory (e.g., assets/js/main.js).

Log IOCs:

• Web server logs showing GET /vulnerable-page/?custom_param=<script>... patterns.
• Error logs with Uncaught SyntaxError or XSS related entries.

Detection Engineering

YARA Rule

rule CVE_2024_53823_DOM_XSS {
    meta:
        description = "Detects vulnerable JavaScript patterns in The Plus Addons for Elementor"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-53823"
    strings:
        $vuln1 = ".innerHTML = " ascii wide
        $vuln2 = ".html(" ascii wide
        $param = "custom_param" ascii wide
    condition:
        all of ($vuln*) and $param
}

Sigma Rule

title: CVE-2024-53823 DOM XSS Detection
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects HTTP requests with XSS payloads targeting The Plus Addons for Elementor
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains:
            - 'custom_param=<script>'
            - 'custom_param=<img'
            - 'custom_param=javascript:'
    condition: selection
falsepositives:
    - Legitimate use of custom_param with safe values
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-53823 DOM XSS Attempt"; flow:to_server,established; content:"custom_param="; http_uri; pcre:"/custom_param=.*(<script|<img|javascript:)/iU"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until an official patch is released.
2. Implement a WAF rule to block XSS payloads in query parameters.
3. Add CSP headers to mitigate script execution:

   Content-Security-Policy: default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval'; require-trusted-types-for 'script';
   

Long-term Fix:

• Monitor the POSIMYTH website or WordPress plugin repository for a patched version.
• Update to version > 5.6.14 once available.
• Conduct a security audit of all third-party plugins.

Workaround:

• If the plugin cannot be disabled, modify the vulnerable JavaScript file to use textContent instead of innerHTML (requires developer access).

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Analyst