CVE-2024-50452: Nexter Blocks Stored XSS Vulnerability

CVE-2024-50452 Overview

CVE-2024-50452 is a Stored Cross-Site Scripting (XSS) vulnerability affecting the POSIMYTH Nexter Blocks plugin (the-plus-addons-for-block-editor) for WordPress. This vulnerability stems from improper neutralization of input during web page generation, allowing authenticated attackers to inject malicious scripts that persist in the database and execute when other users view the affected content.

Critical Impact

Authenticated attackers with contributor-level access or higher can inject persistent malicious scripts into WordPress pages, potentially leading to session hijacking, credential theft, website defacement, and further compromise of site visitors.

Affected Products

• POSIMYTH Nexter Blocks (the-plus-addons-for-block-editor) versions up to and including 3.3.3
• WordPress installations utilizing the vulnerable Nexter Blocks plugin
• Any WordPress site where users with contributor or higher privileges have access to the affected blocks

Discovery Timeline

• 2026-02-20 - CVE CVE-2024-50452 published to NVD
• 2026-02-25 - Last updated in NVD database

Technical Details for CVE-2024-50452

Vulnerability Analysis

This Stored XSS vulnerability exists due to insufficient input sanitization and output encoding within the Nexter Blocks plugin for the WordPress block editor. The plugin fails to properly neutralize user-supplied input before storing it in the database and rendering it on web pages. This allows authenticated users with at least contributor-level privileges to craft malicious payloads that execute arbitrary JavaScript in the browsers of other users who view the affected content.

The vulnerability requires user interaction (a victim must visit a page containing the malicious content), and the attacker must have authenticated access to the WordPress installation. The cross-site nature of this vulnerability means that malicious scripts can impact users across different browser sessions and potentially affect administrative users, leading to privilege escalation scenarios.

Root Cause

The root cause of CVE-2024-50452 is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation). The Nexter Blocks plugin does not adequately sanitize or escape user-controlled input when processing block content. When this unsanitized content is stored and subsequently rendered on the front-end or back-end of the WordPress site, the injected scripts execute in the context of the victim's browser session.

This type of vulnerability typically occurs when:

• Input validation is missing or insufficient for block attributes
• Output encoding is not applied when rendering stored content
• The plugin trusts authenticated user input without proper security controls

Attack Vector

The attack vector for this vulnerability is network-based and requires low attack complexity. An attacker must first authenticate to the WordPress installation with at least contributor-level privileges. Once authenticated, the attacker can create or edit posts/pages using the Nexter Blocks plugin and inject malicious JavaScript code into vulnerable block parameters.

The malicious payload is stored in the WordPress database and executes whenever a user (including administrators) views the affected content. This can lead to session cookie theft, redirection to malicious sites, keylogging, and other client-side attacks. The changed scope in the vulnerability assessment indicates that the impact extends beyond the vulnerable component to affect other components in the system.

For detailed technical analysis of this vulnerability, refer to the Patchstack Vulnerability Report.

Detection Methods for CVE-2024-50452

Indicators of Compromise

• Unexpected JavaScript code or event handlers (such as onerror, onload, onclick) present in post content or block attributes
• Unusual database entries containing <script> tags or encoded malicious payloads in wp_posts or related meta tables
• Reports from users experiencing unexpected redirects, pop-ups, or credential prompts when viewing site content
• Web application firewall logs showing blocked XSS patterns originating from authenticated WordPress users

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block common XSS payloads in POST requests to WordPress admin endpoints
• Enable WordPress audit logging plugins to track content modifications by users with contributor or higher roles
• Perform regular database scans for suspicious script tags, event handlers, and encoded JavaScript patterns in post content
• Monitor browser console errors and network requests for signs of injected scripts executing on page load

Monitoring Recommendations

• Configure SentinelOne Singularity Platform to monitor for anomalous JavaScript execution patterns and suspicious DOM modifications on WordPress sites
• Set up alerts for bulk content modifications or unusual editing patterns by contributor-level users
• Implement Content Security Policy (CSP) headers with violation reporting to detect inline script execution attempts
• Regularly review WordPress user access levels and remove unnecessary contributor or author privileges

How to Mitigate CVE-2024-50452

Immediate Actions Required

• Update the Nexter Blocks plugin to the latest patched version immediately (versions above 3.3.3)
• Review all existing posts and pages created with Nexter Blocks for potentially malicious content
• Audit user accounts with contributor-level access or higher and restrict privileges where not required
• Implement a Web Application Firewall (WAF) with XSS protection rules as an additional defense layer

Patch Information

The vulnerability affects POSIMYTH Nexter Blocks versions through 3.3.3. Users should update to the latest available version that addresses this security issue. Check the WordPress plugin repository or the Patchstack advisory for specific patch version information and update instructions.

Workarounds

• Temporarily disable the Nexter Blocks plugin until a patch can be applied if the plugin is not business-critical
• Restrict user registration and limit contributor/author role assignments to trusted users only
• Implement strict Content Security Policy (CSP) headers to mitigate the impact of XSS by blocking inline script execution
• Use WordPress security plugins that provide real-time XSS filtering for post content and block attributes

# Add Content Security Policy headers to wp-config.php or .htaccess
# Example .htaccess configuration for Apache
<IfModule mod_headers.c>
    Header set Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none';"
</IfModule>

# Verify plugin version via WP-CLI
wp plugin get the-plus-addons-for-block-editor --field=version

# Update plugin to latest version
wp plugin update the-plus-addons-for-block-editor