CVE-2026-59559: RT Mega Menu Plugin XSS Vulnerability

CVE-2026-59559 Overview

CVE-2026-59559 is a stored Cross-Site Scripting (XSS) vulnerability affecting the RT Mega Menu – Mega Menu Builder for Elementor & Gutenberg WordPress plugin in versions up to and including 1.5.1. The flaw lets authenticated users with Subscriber-level privileges inject malicious scripts that execute in other users' browsers. Successful exploitation requires user interaction and can compromise session integrity across trust boundaries. The vulnerability is tracked under CWE-79 (Improper Neutralization of Input During Web Page Generation).

Critical Impact
A low-privileged Subscriber can inject persistent JavaScript that executes against site visitors and administrators, enabling session theft, defacement, or credential harvesting.

Affected Products

RT Mega Menu – Mega Menu Builder for Elementor & Gutenberg (WordPress plugin)
All versions <= 1.5.1
WordPress sites with Subscriber-level registration enabled

Discovery Timeline

2026-07-27 - CVE-2026-59559 published to NVD
2026-07-27 - Last updated in NVD database

Technical Details for CVE-2026-59559

Vulnerability Analysis

The RT Mega Menu plugin fails to properly neutralize user-supplied input before rendering it in menu-building interfaces. An authenticated attacker holding the Subscriber role, the lowest default WordPress privilege, can submit crafted payloads that persist in plugin-managed content. When a higher-privileged user views the affected page, the injected script executes in their browser session.

The scope change flagged in the CVSS vector indicates that exploitation impacts resources beyond the vulnerable component's security scope. This is characteristic of stored XSS in WordPress plugins, where scripts injected by a low-privileged account execute in the browser context of administrators or site visitors. The confidentiality, integrity, and availability impacts are each rated Low.

Root Cause

The root cause is missing or insufficient output encoding when the plugin renders user-controlled input to the DOM. Input validation on the server side does not sanitize HTML control characters, and output routines do not apply context-appropriate escaping such as esc_html(), esc_attr(), or wp_kses(). This aligns with CWE-79, where dynamic content is written to HTML output without safe encoding.

Attack Vector

An attacker registers or uses an existing Subscriber account. The attacker submits a request to a plugin endpoint that stores attacker-controlled content. When a victim, typically an administrator using the mega menu builder, loads the affected page, the stored payload executes. The Patchstack advisory documents the exploitation surface. See the Patchstack WordPress Vulnerability advisory for technical details.

No verified public exploit code is available at this time. The EPSS probability is 0.211% (percentile 11.56), indicating low near-term exploitation likelihood.

Detection Methods for CVE-2026-59559

Indicators of Compromise

Presence of <script>, onerror=, onload=, or javascript: strings in RT Mega Menu database tables or plugin option rows
Unexpected Subscriber account registrations followed by requests to plugin admin-ajax endpoints
Outbound requests from administrator browsers to unfamiliar domains after loading menu builder pages
Anomalous cookies or session tokens transmitted to external hosts from wp-admin sessions

Detection Strategies

Inspect wp_options and plugin-specific tables for HTML or JavaScript payloads within RT Mega Menu configuration entries
Deploy a Web Application Firewall (WAF) rule set that flags XSS payload patterns targeting /wp-admin/admin-ajax.php with plugin action parameters
Enable WordPress activity logging to correlate low-privileged account writes to menu builder objects
Monitor Content Security Policy (CSP) violation reports for inline-script executions on wp-admin pages

Monitoring Recommendations

Alert on new user registrations that immediately interact with plugin-specific REST or AJAX endpoints
Log and review all POST requests to RT Mega Menu handlers from non-administrator roles
Track browser telemetry from administrator workstations for unexpected script execution on wp-admin origins
Retain WordPress and web server logs for at least 90 days to support post-incident review

How to Mitigate CVE-2026-59559

Immediate Actions Required

Update RT Mega Menu to a version later than 1.5.1 once the vendor publishes a fix
Audit existing Subscriber accounts and remove any that are unrecognized or inactive
Disable open user registration under Settings > General if not required for business operations
Review menu builder content for embedded scripts or suspicious HTML and remove offending entries

Patch Information

Refer to the Patchstack WordPress Vulnerability advisory for the latest patch status. Apply the fixed release as soon as it becomes available and validate the plugin version in the WordPress admin dashboard.

Workarounds

Restrict access to the plugin's admin endpoints via .htaccess or server-side ACLs until patched
Deploy a WAF policy that blocks HTML tag and event-handler patterns in plugin POST parameters
Enforce a strict Content Security Policy that disallows inline scripts on wp-admin pages
Temporarily deactivate the RT Mega Menu plugin if the mega menu feature is not essential

bash

# Example: restrict user registration and enforce CSP header via wp-config.php and functions.php
# wp-config.php
define('DISALLOW_FILE_EDIT', true);

# functions.php snippet to send a CSP header for wp-admin
add_action('admin_init', function () {
    header("Content-Security-Policy: default-src 'self'; script-src 'self'; object-src 'none'; base-uri 'self';");
});