CVE-2026-1300: Responsive Header WordPress Plugin XSS Flaw

CVE-2026-1300 Overview

The Responsive Header plugin for WordPress is vulnerable to Stored Cross-Site Scripting (XSS) via multiple plugin settings parameters in all versions up to, and including, 1.0. This vulnerability stems from insufficient input sanitization and output escaping in the plugin's settings handling functionality. Authenticated attackers with administrator-level access can inject arbitrary web scripts into pages that execute whenever a user accesses an injected page.

Critical Impact

This vulnerability allows authenticated administrators to inject persistent malicious scripts that execute in the context of other users' sessions. While requiring high privileges, successful exploitation on multi-site installations could compromise multiple sites within the WordPress network.

Affected Products

• Responsive Header plugin for WordPress versions up to and including 1.0
• WordPress multi-site installations with the Responsive Header plugin enabled
• WordPress installations where unfiltered_html capability has been disabled

Discovery Timeline

• 2026-01-24 - CVE-2026-1300 published to NVD
• 2026-01-26 - Last updated in NVD database

Technical Details for CVE-2026-1300

Vulnerability Analysis

This Stored Cross-Site Scripting vulnerability exists within the Responsive Header plugin's settings page, specifically in the rhp-settings.php file. The vulnerability allows authenticated attackers with administrator privileges to inject malicious JavaScript code through multiple plugin settings parameters. When stored, these malicious scripts persist in the WordPress database and execute in the browsers of any users who subsequently access pages where the injected content is rendered.

The attack requires network access and administrator-level authentication, but does not require user interaction once the malicious payload is stored. The scope of the vulnerability extends beyond the vulnerable component itself, as injected scripts can potentially access content and perform actions in the context of the victim's session.

This vulnerability specifically affects WordPress multi-site installations and single-site installations where the unfiltered_html capability has been explicitly disabled. In standard single-site configurations with default settings, administrators typically have the unfiltered_html capability, which already allows HTML injection through normal means.

Root Cause

The root cause of CVE-2026-1300 is insufficient input sanitization and output escaping in the plugin's settings handling code. When plugin settings are saved, user-supplied input is not properly sanitized before being stored in the database. Additionally, when these settings are rendered on the frontend or in the admin area, the stored values are not adequately escaped before output, allowing any injected script content to execute in users' browsers.

The vulnerable code is located in rhp-settings.php at line 103, where multiple settings parameters fail to implement proper WordPress sanitization functions such as sanitize_text_field(), esc_html(), or wp_kses() for input validation and output encoding.

Attack Vector

The attack leverages network-based access to the WordPress administration interface. An attacker with administrator credentials navigates to the Responsive Header plugin settings page and injects malicious JavaScript payloads into one or more vulnerable settings fields.

Due to the high complexity conditions required (multi-site environment or disabled unfiltered_html), exploitation requires specific WordPress configurations. Once successfully injected, the stored script executes whenever any user—including other administrators or site visitors—loads a page that renders the compromised settings. This could enable session hijacking, credential theft, defacement, or further attacks against site users.

The vulnerability mechanism involves the plugin accepting arbitrary HTML and JavaScript through settings fields and storing these values without sanitization. When rendered, the malicious content is output without proper escaping, resulting in script execution. For detailed technical analysis, see the Wordfence Vulnerability Report and the plugin source code.

Detection Methods for CVE-2026-1300

Indicators of Compromise

• Unexpected JavaScript code present in Responsive Header plugin settings in the wp_options database table
• Unusual <script> tags or JavaScript event handlers (e.g., onerror, onload) stored in plugin configuration values
• Reports from users experiencing unexpected browser behavior, redirects, or pop-ups when visiting the site
• Web application firewall (WAF) logs showing blocked XSS patterns originating from plugin settings pages

Detection Strategies

• Implement Content Security Policy (CSP) headers to detect and block unauthorized inline script execution
• Deploy WordPress-specific security plugins that scan database content for stored XSS payloads
• Monitor plugin settings changes through WordPress audit logging plugins to track modifications by administrators
• Regularly scan the WordPress database for suspicious patterns including encoded JavaScript, data URIs, and event handlers

Monitoring Recommendations

• Enable and review WordPress admin activity logs for changes to Responsive Header plugin settings
• Configure web application firewalls to alert on XSS pattern submissions to WordPress admin endpoints
• Implement browser-based security monitoring to detect anomalous script execution on WordPress sites
• Establish baseline monitoring of plugin configuration tables and alert on unexpected modifications

How to Mitigate CVE-2026-1300

Immediate Actions Required

• Audit current Responsive Header plugin settings for any suspicious or unexpected JavaScript content
• Temporarily disable the Responsive Header plugin if it is not critical to site functionality until a patched version is available
• Review WordPress administrator accounts and remove any unnecessary privileged access
• Implement Web Application Firewall rules to filter XSS payloads in plugin settings submissions

Patch Information

As of the last update on 2026-01-26, no patch has been confirmed for the Responsive Header plugin. Site administrators should monitor the WordPress Plugin Directory for updates beyond version 1.0 that address this vulnerability. Consider contacting the plugin author to inquire about security updates.

Until an official patch is released, organizations should evaluate whether the plugin is essential to operations and consider alternative plugins with better security track records.

Workarounds

• Restrict administrator access to only trusted users who require plugin management capabilities
• On multi-site installations, limit Super Admin access and review network-wide plugin settings
• Implement additional input validation at the server level using security plugins like Wordfence or Sucuri
• Consider enabling unfiltered_html capability for administrators on single-site installations (note: this allows HTML by design, reducing the specific attack surface but introducing other risks)

# Review current plugin settings in WordPress database
wp db query "SELECT option_name, option_value FROM wp_options WHERE option_name LIKE '%responsive_header%';"

# Disable the plugin via WP-CLI if suspicious content is found
wp plugin deactivate responsive-header

# Add Content Security Policy header via .htaccess (Apache)
# Add to .htaccess file:
# Header set Content-Security-Policy "script-src 'self'; object-src 'none';"