CVE-2026-6048: Flipbox Addon for Elementor XSS Vulnerability

CVE-2026-6048 Overview

The Flipbox Addon for Elementor plugin for WordPress contains a Stored Cross-Site Scripting (XSS) vulnerability in the Flipbox widget's button URL custom_attributes field. The vulnerability exists in all versions up to and including 2.1.1 due to insufficient validation of custom attribute names. The plugin incorrectly uses esc_html() on the attribute name, which fails to prevent event handler attributes such as onmouseover and onclick from being injected.

This vulnerability allows authenticated attackers with author-level access or higher to inject arbitrary web scripts into pages. These malicious scripts execute whenever any user accesses an injected page, potentially leading to session hijacking, credential theft, or further compromise of the WordPress installation.

Critical Impact

Authenticated attackers can inject persistent malicious scripts that execute in the context of any user viewing affected pages, including administrators.

Affected Products

• Flipbox Addon for Elementor (Ultimate Flipbox Addon for Elementor) versions up to and including 2.1.1
• WordPress installations running the vulnerable plugin versions
• Sites using Elementor page builder with the Flipbox Addon widget

Discovery Timeline

• April 18, 2026 - CVE-2026-6048 published to NVD
• April 22, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6048

Vulnerability Analysis

This Stored Cross-Site Scripting vulnerability stems from improper output encoding of user-supplied custom attribute names in the Flipbox widget component. The plugin processes custom attributes for button URLs but applies esc_html() encoding, which is designed for HTML content escaping rather than attribute name validation.

When rendering the widget's output, the plugin fails to validate that custom attribute names do not contain JavaScript event handlers. As a result, attackers can specify event handler attributes like onmouseover, onclick, onfocus, or onerror as attribute names, with malicious JavaScript as the attribute value.

The vulnerability requires authentication with at least author-level privileges, which limits the attack surface but still presents significant risk in multi-author WordPress environments or sites where user registration is enabled with elevated default roles.

Root Cause

The root cause is the incorrect use of esc_html() for sanitizing HTML attribute names. The esc_html() function is designed to escape HTML entities within content, not to validate or sanitize attribute names. Proper attribute name validation should use an allowlist approach, permitting only safe attributes such as class, id, data-*, title, and similar non-executable attributes while explicitly blocking event handler attributes.

The vulnerable code can be found in the plugin's frontend rendering classes, specifically in class-ufae-frontend-item.php and class-ufae-frontend-loop.php, where custom attributes are processed and output to the page without proper validation.

Attack Vector

The attack requires an authenticated user with author-level or higher privileges to access the WordPress editor and create or modify a page or post containing the Flipbox widget. The attacker adds a custom attribute to the Flipbox button URL field with an event handler name (e.g., onmouseover) and malicious JavaScript as the value.

Once the page is published, any visitor who interacts with the injected element will trigger the malicious script execution. Since the payload is stored in the database and rendered server-side, the attack persists across page loads and affects all users who view the compromised content.

The attack can be used to steal session cookies, redirect users to malicious sites, perform actions on behalf of authenticated users, or inject additional malicious content into the page.

Detection Methods for CVE-2026-6048

Indicators of Compromise

• Presence of event handler attributes (onmouseover, onclick, onfocus, onerror, onload, etc.) in Flipbox widget custom attributes stored in the WordPress database
• Unusual JavaScript code embedded within widget configuration in post metadata
• Reports of unexpected browser behavior or redirects when viewing pages containing Flipbox widgets
• Web application firewall (WAF) alerts indicating XSS patterns in WordPress admin requests

Detection Strategies

• Review WordPress post metadata for suspicious custom attribute configurations containing JavaScript event handlers
• Implement Content Security Policy (CSP) headers to detect and prevent inline script execution
• Monitor WordPress admin activity logs for unusual widget configuration changes
• Deploy web application firewall rules that detect XSS patterns in POST requests to WordPress admin endpoints

Monitoring Recommendations

• Enable verbose logging for WordPress admin actions, particularly page and post editing
• Configure alerting for CSP violation reports that may indicate attempted or successful XSS exploitation
• Regularly audit pages containing Flipbox widgets for suspicious custom attribute values
• Monitor for unauthorized modifications to published content by author-level users

How to Mitigate CVE-2026-6048

Immediate Actions Required

• Update the Flipbox Addon for Elementor plugin to version 2.1.2 or later immediately
• Review all existing pages and posts using the Flipbox widget for potentially injected malicious content
• Audit user accounts with author-level or higher privileges for any unauthorized activity
• Consider temporarily disabling the plugin if immediate update is not possible

Patch Information

The vulnerability has been addressed in version 2.1.2 of the Flipbox Addon for Elementor plugin. The patch modifies the custom attribute handling code in both class-ufae-frontend-item.php and class-ufae-frontend-loop.php to properly validate attribute names. Updated code can be reviewed in the WordPress Plugin Repository for version 2.1.2.

For additional vulnerability details, see the Wordfence Vulnerability Report.

Workarounds

• Restrict author-level and higher privileges to trusted users only until the plugin is updated
• Implement a Web Application Firewall (WAF) with XSS protection rules to filter malicious payloads
• Temporarily disable the Flipbox Addon for Elementor plugin if update is not immediately feasible
• Deploy Content Security Policy headers to mitigate the impact of successful XSS injection

# Example: Add Content Security Policy header in Apache .htaccess
# Add to WordPress root .htaccess file
Header set Content-Security-Policy "script-src 'self'; object-src 'none'"