CVE-2021-24891: Elementor Website Builder XSS Vulnerability

CVE-2021-24891 Overview

CVE-2021-24891 is a DOM-based Cross-Site Scripting (XSS) vulnerability affecting the Elementor Website Builder plugin for WordPress. The vulnerability exists because the plugin does not properly sanitize or escape user input that is appended to the DOM via a malicious hash parameter. This allows attackers to inject and execute arbitrary JavaScript code in the context of a victim's browser session.

Critical Impact

Attackers can execute arbitrary JavaScript in victims' browsers, potentially leading to session hijacking, credential theft, malware distribution, or website defacement on affected WordPress sites.

Affected Products

• Elementor Website Builder WordPress plugin versions prior to 3.4.8

Discovery Timeline

• 2021-11-23 - CVE-2021-24891 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-24891

Vulnerability Analysis

This DOM-based XSS vulnerability occurs within the Elementor Website Builder's lightbox functionality. The plugin processes URL hash fragments without proper sanitization before inserting them into the Document Object Model (DOM). When a user visits a specially crafted URL containing malicious JavaScript in the hash portion, the script executes within the security context of the vulnerable WordPress site.

DOM-based XSS differs from traditional reflected or stored XSS in that the malicious payload never reaches the server. Instead, the vulnerability is entirely client-side, with the browser's JavaScript engine processing and executing the attacker-controlled input. This makes the attack particularly difficult to detect through traditional server-side security monitoring.

Root Cause

The root cause of this vulnerability is improper input validation and output encoding in the Elementor plugin's JavaScript code. Specifically, the lightbox component reads data from the URL hash (the portion after the # symbol) and directly incorporates it into DOM operations without sanitizing the input. This violates the fundamental security principle of treating all user input as untrusted.

The vulnerable code path involves the lightbox feature parsing hash parameters to determine which content to display. An attacker can craft a malicious hash containing JavaScript that, when processed by the vulnerable code, results in script execution.

Attack Vector

The attack requires user interaction—specifically, the victim must click on a malicious link or be redirected to a URL containing the XSS payload in the hash fragment. The attacker constructs a URL targeting a WordPress site running the vulnerable Elementor plugin version.

Since the payload resides in the URL hash, it may bypass certain security controls that only inspect server-bound traffic. The attack can be delivered through phishing emails, malicious advertisements, compromised third-party sites, or social media links.

When a victim clicks the malicious link, their browser loads the legitimate WordPress page, but the Elementor JavaScript processes the malicious hash and injects the attacker's script into the DOM. This script then executes with full access to the page context, enabling actions such as stealing cookies, capturing keystrokes, or redirecting users to malicious sites.

Detection Methods for CVE-2021-24891

Indicators of Compromise

• Suspicious URL patterns containing encoded JavaScript or HTML in hash fragments targeting WordPress sites
• Unexpected outbound connections from visitor browsers to unknown external domains
• User reports of unexpected popups, redirects, or authentication prompts on your WordPress site
• Web server logs showing referrer URLs with unusual hash parameters

Detection Strategies

• Implement Content Security Policy (CSP) headers to detect and block inline script execution attempts
• Deploy browser-based security monitoring to detect DOM manipulation anomalies
• Monitor for unusual JavaScript execution patterns in client-side error tracking systems
• Review WordPress site access logs for URLs containing suspicious hash fragments

Monitoring Recommendations

• Enable WordPress security plugin logging to track potential exploitation attempts
• Set up alerts for Content Security Policy violation reports
• Monitor Elementor plugin version across all WordPress installations in your environment
• Implement real-time browser security monitoring for high-value WordPress sites

How to Mitigate CVE-2021-24891

Immediate Actions Required

• Update Elementor Website Builder plugin to version 3.4.8 or later immediately
• Audit all WordPress installations for vulnerable Elementor versions
• Implement Content Security Policy headers to mitigate XSS impact
• Review site access logs for potential exploitation attempts

Patch Information

The vulnerability was addressed in Elementor Website Builder version 3.4.8. The fix implements proper input sanitization and output encoding for hash parameters processed by the lightbox functionality. Site administrators should update through the WordPress plugin management interface or download the patched version directly from the WordPress plugin repository.

For detailed vulnerability information, see the WPScan Vulnerability Details and the JBelamor XSS Analysis.

Workarounds

• Temporarily disable the Elementor lightbox feature if immediate patching is not possible
• Implement a Web Application Firewall (WAF) rule to sanitize or block suspicious hash parameters
• Deploy strict Content Security Policy headers to prevent inline script execution
• Consider temporarily deactivating the Elementor plugin on critical sites until patching is complete

# Add Content Security Policy header to WordPress .htaccess
# This helps mitigate XSS attacks by restricting script sources
Header set Content-Security-Policy "default-src 'self'; script-src 'self' 'unsafe-inline' https://trusted-cdn.example.com; style-src 'self' 'unsafe-inline';"