CVE-2025-66066

Executive Summary

CVE-2025-66066 is a Stored Cross-Site Scripting (XSS) vulnerability in the Envo Extra WordPress plugin (slug: envo-extra) developed by EnvoThemes. This vulnerability allows an authenticated attacker with contributor-level privileges or higher to inject arbitrary web scripts into pages or posts. When an administrator or other user views the compromised content, the injected script executes in their browser, potentially leading to session hijacking, credential theft, or defacement.

The vulnerability exists in versions 1.9.11 and earlier. As of this report, no official patch has been released by the vendor. The CVSS score is 6.5 (Medium), but the risk is elevated in multi-tenant WordPress environments or sites with many contributors.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Since WordPress plugins are a common supply chain vector, any site using Envo Extra <= 1.9.11 is at risk. Attackers may target the plugin’s update mechanism or inject malicious code through compromised contributor accounts.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): Low (L) – Attacker needs contributor-level access.
• User Interaction (UI): Required (R) – Victim must view the malicious content.
• Scope (SC): Changed (C) – The injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure possible.
• Integrity (I): Low (L) – Content can be modified.
• Availability (A): Low (L) – Minor disruption possible.

Threat Level: Medium (6.5) – Exploitation requires authentication but can lead to significant impact in shared environments.

Deep Dive & Mechanics

The vulnerability stems from improper neutralization of user-supplied input in the Envo Extra plugin. The plugin likely processes shortcodes, custom fields, or widget options without proper sanitization or output encoding. When a contributor creates or edits a post/page and inserts a malicious payload (e.g., via a shortcode attribute or custom field), the payload is stored in the database. Upon rendering, the payload executes in the context of the victim’s browser.

Root Cause: The plugin uses functions like echo or the_content filter without applying esc_html(), wp_kses(), or similar WordPress sanitization functions.

Attack Vector:

1. Attacker logs in as a contributor.
2. Creates a new post or page.
3. Inserts a malicious script payload into a field processed by Envo Extra (e.g., a shortcode parameter).
4. Publishes or saves the post as draft.
5. Administrator or other user views the post.
6. Script executes, stealing cookies or performing actions on behalf of the victim.

Vulnerable vs. Patched Code

Vulnerable Code (envo-extra <= 1.9.11):

// Example: Shortcode handler that outputs user input without sanitization
function envo_extra_shortcode($atts) {
    $title = $atts['title'];
    return "<h2>$title</h2>";
}
add_shortcode('envo_extra_box', 'envo_extra_shortcode');

Patched Code (hypothetical fix):

function envo_extra_shortcode($atts) {
    $title = isset($atts['title']) ? esc_html($atts['title']) : '';
    return "<h2>$title</h2>";
}
add_shortcode('envo_extra_box', 'envo_extra_shortcode');

The fix uses esc_html() to encode HTML entities, preventing script injection.

Exploitation & Lab Setup

Red Team (Proof of Concept)

Since no public exploit exists, the following is a conceptual payload for testing:

1. Prerequisites: WordPress site with Envo Extra <= 1.9.11, contributor account.
2. Payload: In a post’s content or custom field, insert:

   [envo_extra_box title="<script>alert('XSS')</script>"]
   

3. Trigger: An administrator views the post. The script executes.

Note: This is a stored XSS; the payload persists until removed.

Blue Team (Detection & Hardening)

• Input Validation: Ensure all user inputs are sanitized with wp_kses() or esc_html().
• Output Encoding: Use esc_html(), esc_attr(), or wp_kses_post() when rendering data.
• Content Security Policy (CSP): Implement a strict CSP header to block inline scripts.
• User Role Management: Restrict contributor permissions; use a plugin to limit shortcode usage.
• Web Application Firewall (WAF): Deploy rules to block <script> tags in post content.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None available – no exploit code released)
• Network Indicators:
  • Outbound connections to attacker-controlled domains (e.g., evil.com).
  • HTTP requests containing <script> tags in POST data to wp-admin/post.php.
• Log Artifacts:
  • WordPress debug log entries showing wp_kses failures.
  • Apache/Nginx access logs with POST /wp-admin/post.php and suspicious payloads.
• Database Indicators:
  • Rows in wp_posts or wp_postmeta containing <script> tags.

Detection Engineering

YARA Rule

rule CVE_2025_66066_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads targeting Envo Extra plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-66066"
    strings:
        $payload1 = /<script[^>]*>.*?<\/script>/is
        $payload2 = /onerror\s*=\s*["']?[^"']*["']?/i
        $payload3 = /javascript\s*:/i
    condition:
        any of them
}

Sigma Rule

title: Stored XSS via Envo Extra Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects stored XSS attempts in WordPress posts using Envo Extra shortcodes
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        c-uri: '/wp-admin/post.php*'
        cs-uri-query|contains: 'envo_extra_box'
        sc-status: 200
    condition: selection
falsepositives:
    - Legitimate use of shortcodes with safe content
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-66066 Stored XSS Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; content:"envo_extra_box"; http_client_body; pcre:"/<script[^>]*>.*?<\/script>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Audit all posts/pages created by contributors for malicious content.
3. Implement a Web Application Firewall (WAF) with rules to block XSS payloads.

Long-Term Fix:

• The vendor must release a patched version (>= 1.9.12) that sanitizes all user inputs.
• Apply the fix shown in the "Vulnerable vs. Patched Code" section.

Workarounds:

• Use a security plugin (e.g., Wordfence) to block XSS attempts.
• Restrict contributor roles to trusted users only.
• Enable DISALLOW_UNFILTERED_HTML in wp-config.php.

Valters IT
Securing Digital Frontiers