CVE-2025-9565: Blocksy Companion Plugin XSS Vulnerability

CVE-2025-9565 Overview

The Blocksy Companion plugin for WordPress contains a Stored Cross-Site Scripting (XSS) vulnerability in the blocksy_newsletter_subscribe shortcode. The flaw affects all versions up to and including 2.1.10. Insufficient input sanitization and output escaping on user-supplied shortcode attributes allow authenticated attackers with contributor-level access or above to inject arbitrary web scripts. Injected scripts execute in the browsers of any users who visit an affected page. The issue is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation).

Critical Impact
Authenticated contributors can persist JavaScript payloads in pages, enabling session theft, administrator account takeover, and drive-by attacks against site visitors.

Affected Products

Blocksy Companion plugin for WordPress, all versions ≤ 2.1.10
WordPress sites using the blocksy_newsletter_subscribe shortcode
Sites that grant contributor-level access or higher to untrusted users

Discovery Timeline

2025-09-17 - CVE-2025-9565 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-9565

Vulnerability Analysis

The vulnerability resides in the newsletter subscribe extension shipped with Blocksy Companion. The blocksy_newsletter_subscribe shortcode accepts user-controlled attributes and renders them into the page markup. The plugin does not adequately sanitize these attributes on input or escape them on output. As a result, an authenticated user with permission to create or edit posts can embed the shortcode with malicious attribute values that contain JavaScript. The payload is stored in post content and executed each time a visitor loads the affected page.

Affected code paths are visible in the plugin's public repository, specifically the newsletter subscribe extension and the helpers module.

Root Cause

The root cause is missing input validation and output encoding on shortcode attributes. The rendering helper concatenates attribute values into HTML without invoking WordPress escaping functions such as esc_attr() or esc_html(). Any attribute that reaches the DOM as raw text can carry executable script content.

Attack Vector

An attacker requires an authenticated WordPress account with contributor-level privileges or higher. The attacker inserts the blocksy_newsletter_subscribe shortcode into a draft or published post and supplies attribute values containing script content. When an administrator previews the post or a visitor accesses the page, the browser executes the injected script in the site's origin context. This enables session hijacking, credential harvesting, forced administrative actions, and redirection to attacker-controlled infrastructure.

No verified proof-of-concept code is published for this issue. For technical detail, see the vendor commit in Blocksy changeset 3360000 and the Wordfence vulnerability analysis.

Detection Methods for CVE-2025-9565

Indicators of Compromise

Posts or pages containing the blocksy_newsletter_subscribe shortcode with attributes that include <script>, onerror=, onload=, or javascript: sequences.
Unexpected outbound requests from browser sessions to unknown domains when rendering pages that use the shortcode.
New or modified administrator accounts created shortly after contributors edited content.

Detection Strategies

Query the wp_posts table for shortcode instances: SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%blocksy_newsletter_subscribe%'; and inspect each match for suspicious attributes.
Review web server access logs for POST requests to /wp-admin/post.php from contributor accounts followed by anomalous GET traffic on the rendered pages.
Enable Content Security Policy (CSP) reporting to capture script-src violations originating from affected pages.

Monitoring Recommendations

Monitor WordPress role changes, plugin edits, and new administrator account creation events.
Track authentication events from contributor accounts, especially session activity outside normal working hours.
Alert on plugin version drift for blocksy-companion across managed WordPress fleets.

How to Mitigate CVE-2025-9565

Immediate Actions Required

Update Blocksy Companion to the version published in changeset 3360000 or later, which supersedes 2.1.10.
Audit all posts and pages for the blocksy_newsletter_subscribe shortcode and remove any suspicious attributes.
Review contributor and author accounts, disable inactive accounts, and enforce strong password and multi-factor authentication policies.

Patch Information

The vendor addressed the issue in the Blocksy Companion plugin via changeset 3360000, which adds proper escaping to the newsletter subscribe helper. Apply the update through the WordPress plugin dashboard or via WP-CLI.

Workarounds

Restrict contributor and author roles to trusted users only until the plugin is updated.
Temporarily deactivate the Blocksy Companion newsletter subscribe extension if patching is not immediately possible.
Deploy a Web Application Firewall (WAF) rule that blocks shortcode attributes containing <script> or event handler patterns in post submissions.

bash

# Configuration example: update Blocksy Companion via WP-CLI
wp plugin update blocksy-companion
wp plugin get blocksy-companion --field=version