CVE-2025-50046

Executive Summary

CVE-2025-50046 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin WPComplete by StellarWP. This flaw allows an authenticated attacker with contributor-level privileges or higher to inject arbitrary JavaScript into web pages generated by the plugin. The injected script executes in the context of any user viewing the affected page, leading to session hijacking, credential theft, or defacement. The vulnerability affects all versions up to and including 2.9.5. No official patch has been released at the time of analysis. The CVSS score is 6.5 (Medium), but the real-world impact is elevated due to the stored nature of the XSS and the widespread use of WordPress.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress plugin repository and third-party marketplaces. Users who installed WPComplete from any source are at risk. The lack of a patch means that supply chain integrity is compromised until the vendor releases an update. Organizations should treat this as a high-priority supply chain risk and consider removing the plugin until a fix is available.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): Low (L) – An attacker needs contributor-level access to the WordPress site.
• User Interaction (UI): Required (R) – The victim must visit the compromised page.
• Scope (S): Changed (C) – The injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure possible.
• Integrity (I): Low (L) – Limited ability to modify content.
• Availability (A): Low (L) – Limited impact on availability.

Threat Level: Medium (6.5) – However, due to the stored XSS nature and the prevalence of WordPress, the operational risk is considered High for unpatched installations.

Deep Dive & Mechanics

The vulnerability stems from improper neutralization of user-supplied input within the WPComplete plugin. The plugin likely processes user-submitted data (e.g., task descriptions, comments, or progress updates) and renders it on the frontend without adequate sanitization or output encoding. An attacker with contributor-level access can inject malicious HTML/JavaScript payloads into these fields. When an administrator or other user views the affected page, the payload executes in their browser.

The root cause is a failure to apply context-aware escaping (e.g., esc_html(), esc_js(), or wp_kses()) before outputting user data. This is a classic Stored XSS pattern in WordPress plugins.

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical comparison based on common remediation patterns.

Vulnerable Code (wpcomplete/includes/class-frontend.php):

function display_task_comment($comment) {
    echo '<div class="task-comment">' . $comment->content . '</div>';
}

Patched Code (Hypothetical):

function display_task_comment($comment) {
    echo '<div class="task-comment">' . esc_html($comment->content) . '</div>';
}

The patched version uses esc_html() to encode HTML special characters, preventing script injection.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A WordPress instance with WPComplete <= 2.9.5 installed and activated.
• A user account with at least Contributor role.

Steps:

1. Log in as a contributor.
2. Navigate to a WPComplete feature that accepts user input (e.g., adding a task comment).
3. Inject the following payload into the input field:

   <script>alert('XSS')</script>
   

4. Save the entry.
5. As an administrator, view the page containing the comment. The script executes.

Advanced Payload (Session Hijacking):

<script>
fetch('/wp-admin/admin-ajax.php?action=your_action&cookie='+document.cookie);
</script>

Blue Team (Detection & Response)

Detection:

• Monitor for unusual input patterns in WPComplete fields (e.g., <script>, onerror=, javascript:).
• Review WordPress user activity logs for suspicious edits by contributors.
• Use the detection rules provided below.

Response:

1. Immediately disable the WPComplete plugin.
2. Scan the WordPress database for injected payloads using a tool like wp-cli:

   wp db query "SELECT * FROM wp_posts WHERE post_content LIKE '%<script>%'"
   

3. Remove any malicious content.
4. Rotate all admin session tokens and passwords.
5. Apply virtual patching via WAF rules (see below).

Indicators of Compromise (IOCs)

• File System:
  • Presence of unexpected JavaScript in WPComplete database entries (e.g., wp_wpcomplete_tasks, wp_wpcomplete_comments).
• Network:
  • Outbound connections to known malicious domains from the WordPress server.
• Logs:
  • Repeated failed login attempts followed by successful contributor logins.
  • Unusual POST requests to wp-admin/admin-ajax.php with action parameters related to WPComplete.

Detection Engineering

YARA Rule

rule CVE_2025_50046_WPComplete_XSS {
    meta:
        description = "Detects stored XSS payloads in WPComplete plugin data"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-50046"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /on\w+\s*=\s*['\"].*?['\"]/is
        $xss3 = /javascript\s*:/is
    condition:
        any of them
}

Sigma Rule

title: Stored XSS in WPComplete Plugin
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects potential stored XSS attempts in WPComplete plugin input fields
author: Valters IT
logsource:
    category: application
    product: wordpress
detection:
    selection:
        eventSource: 'wpcomplete'
        requestMethod: 'POST'
        requestBody|contains:
            - '<script'
            - 'onerror='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in admin panels (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-50046 WPComplete Stored XSS Payload"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=wpcomplete"; http_client_body; pcre:"/(<script|onerror=|javascript:)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the WPComplete plugin until a patch is released.
2. Apply a virtual patch using a Web Application Firewall (WAF) to block XSS payloads in POST requests to WPComplete endpoints.
3. Audit user roles – Remove contributor access from untrusted users.

Long-Term Fix:

• Monitor the StellarWP website for an official patch (version > 2.9.5).
• Once patched, update the plugin immediately and re-enable it.

Workaround:

• If the plugin cannot be disabled, implement output escaping via a custom mu-plugin:

  add_filter('wpcomplete_output_comment', 'esc_html');
  

Valters IT
Securing Digital Frontiers