CVE-2025-1625

Executive Summary

CVE-2025-1625 is a Stored Cross-Site Scripting (XSS) vulnerability in the Qi Blocks WordPress plugin (versions before 1.4). The plugin fails to properly validate and escape user-supplied input within its "Counter" block options before rendering them on a page or post. This allows authenticated users with at least the Contributor role to inject arbitrary JavaScript, which executes in the context of any visitor viewing the affected content. The vulnerability is classified as a WordPress ecosystem issue and does not involve Apache or Nginx.

Supply Chain & Package Security

This vulnerability affects the Qi Blocks WordPress plugin, distributed via the official WordPress plugin repository. Users should verify they are running version 1.4 or later. No known supply chain compromise has been reported, but the unpatched status for older versions poses a risk to any site using the plugin.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
• Base Score: 6.1 (Medium)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (Contributor role)
• User Interaction: None
• Scope: Changed (impacts other components)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

Threat Level: Medium. Exploitation requires authenticated access with Contributor privileges, but the stored XSS can affect all site visitors, including administrators, leading to session hijacking or defacement.

Deep Dive & Mechanics

The vulnerability resides in the Counter block of the Qi Blocks plugin. When a user with Contributor or higher privileges inserts a Counter block into a post or page, the plugin does not sanitize or escape certain block options (e.g., counter_start, counter_end, counter_prefix, counter_suffix) before outputting them in the HTML. An attacker can inject malicious JavaScript into these fields, which is then stored in the WordPress database and executed when any user views the affected page.

The root cause is a lack of output escaping in the block's render callback. WordPress provides functions like esc_html() and wp_kses_post() for safe output, but the plugin uses raw echo statements without sanitization.

Vulnerable vs. Patched Code

Vulnerable Code (version < 1.4):

// In the render callback for the Counter block
echo '<div class="counter-start">' . $attributes['counter_start'] . '</div>';
echo '<div class="counter-end">' . $attributes['counter_end'] . '</div>';

Patched Code (version 1.4):

// Properly escaped output
echo '<div class="counter-start">' . esc_html( $attributes['counter_start'] ) . '</div>';
echo '<div class="counter-end">' . esc_html( $attributes['counter_end'] ) . '</div>';

The patch applies esc_html() to all user-controlled attributes before output, preventing XSS.

Exploitation & Lab Setup

Red Team (Exploitation)

1. Prerequisites: WordPress site with Qi Blocks plugin < 1.4, an account with Contributor role or higher.
2. Steps:
   • Log in as a Contributor.
   • Create a new post or edit an existing one.
   • Add a "Counter" block.
   • In the block settings, inject a payload into the "Start Value" or "End Value" field, e.g.:

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

   • Publish or update the post.
   • Any visitor viewing the post will trigger the script.

Example Payload:

"><img src=x onerror=alert(document.cookie)>

Blue Team (Detection & Hardening)

• Web Application Firewall (WAF): Deploy rules to block common XSS patterns in POST data for wp-admin/post.php and wp-admin/post-new.php.
• Input Validation: Ensure all user inputs are sanitized using WordPress functions like sanitize_text_field() and wp_kses_post().
• Content Security Policy (CSP): Implement a strict CSP header to mitigate XSS impact:

  Content-Security-Policy: default-src 'self'; script-src 'self'; object-src 'none';
  

• User Role Review: Limit the number of users with Contributor or higher roles.

Indicators of Compromise (IOCs)

• File Indicators:
  • Modified posts/pages containing <script> tags or event handlers (e.g., onerror, onload).
  • Suspicious entries in the wp_posts table with post_content containing XSS payloads.
• Network Indicators:
  • Outbound connections to attacker-controlled domains from the WordPress server.
  • HTTP requests to wp-admin/admin-ajax.php with unusual payloads.
• Log Indicators:
  • Repeated 403 errors from WAF blocking XSS attempts.
  • User activity logs showing unusual block configuration changes.

Detection Engineering

YARA Rule

rule CVE_2025_1625_Qi_Blocks_XSS {
    meta:
        description = "Detects Qi Blocks plugin files with unescaped output in Counter block"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-1625"
    strings:
        $unescaped1 = "counter_start" ascii nocase
        $unescaped2 = "counter_end" ascii nocase
        $echo = "echo" ascii nocase
        $esc_html = "esc_html" ascii nocase
    condition:
        all of ($unescaped*) and $echo and not $esc_html
}

Sigma Rule

title: CVE-2025-1625 Qi Blocks Stored XSS Detection
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects stored XSS payloads in WordPress posts via Qi Blocks plugin
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        http.method: POST
        http.url: "/wp-admin/post.php*"
        http.body|contains: 
            - "<script>"
            - "onerror="
            - "onload="
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in posts (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-1625 Qi Blocks Stored XSS Payload"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; content:"<script>"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Upgrade the Qi Blocks plugin to version 1.4 or later.
2. Workaround: If upgrade is not possible, disable the Counter block by removing its registration in the plugin code or using a security plugin to block Contributor-level users from editing posts.
3. Long-term: Implement a Web Application Firewall (WAF) with XSS protection, enforce strict Content Security Policy (CSP), and regularly audit user roles and permissions.

Valters IT
Securing Digital Frontiers