CVE-2024-3734

Executive Summary

CVE-2024-3734 is a critical unauthenticated arbitrary shortcode execution vulnerability in the FOX – Currency Switcher Professional for WooCommerce WordPress plugin (versions up to and including 1.4.1.8). This vulnerability allows any unauthenticated attacker to execute arbitrary WordPress shortcodes, which can lead to data theft, privilege escalation, or site compromise depending on the shortcodes provided by other installed plugins. The vulnerability is classified as a CWE-94: Improper Control of Generation of Code ('Code Injection') and has a CVSS score of 6.5 (Medium). No official patch has been released as of this analysis.

Supply Chain & Package Security

This vulnerability affects a commercial WordPress plugin distributed via the FOX plugin marketplace. Since it is not an open-source package (NPM, PyPI, Go, Ruby), supply chain risks are limited to the plugin's update mechanism. Users should verify the integrity of plugin updates by checking checksums provided by the vendor.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component remains the same.
• Confidentiality (C): Low (L) – Limited data exposure possible.
• Integrity (I): Low (L) – Limited modification possible.
• Availability (A): Low (L) – Limited service disruption possible.

Threat Level: Medium. While the CVSS score is 6.5, the actual impact depends heavily on the WordPress environment. If plugins like wp-config.php backup or user management shortcodes exist, the severity can escalate to critical.

Deep Dive & Mechanics

The vulnerability resides in the woocommerce-currency-switcher plugin's handling of shortcodes. The plugin registers a shortcode (e.g., [woocs]) but fails to sanitize or restrict which shortcodes can be executed via user-supplied input. An unauthenticated attacker can craft a request that passes arbitrary shortcode names to the plugin's processing function, which then executes them without validation.

Root Cause: The plugin uses do_shortcode() on user-controlled input without first checking if the shortcode is allowed. This allows an attacker to execute any registered shortcode, including those from other plugins.

Exploitability: The vulnerability is trivially exploitable via HTTP GET or POST requests. No authentication is required.

Vulnerable vs. Patched Code

Since no patch is available, we compare the vulnerable code to a hypothetical secure implementation.

Vulnerable Code (v1.4.1.8):

// In woocommerce-currency-switcher.php
add_shortcode('woocs', 'woocs_shortcode_handler');
function woocs_shortcode_handler($atts, $content = null) {
    // Directly executes user-supplied shortcode without validation
    return do_shortcode($content);
}

Patched Code (Hypothetical):

// In woocommerce-currency-switcher.php
add_shortcode('woocs', 'woocs_shortcode_handler');
function woocs_shortcode_handler($atts, $content = null) {
    // Whitelist allowed shortcodes
    $allowed_shortcodes = array('woocs', 'woocs_converter');
    if (in_array($content, $allowed_shortcodes)) {
        return do_shortcode($content);
    }
    return '';
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• A WordPress site with FOX – Currency Switcher Professional <= 1.4.1.8 installed and activated.
• Another plugin that provides a useful shortcode (e.g., [user_info] or [wp-config-viewer]).

Exploit Steps:

1. Identify the vulnerable endpoint: http://target.com/?woocs=1&content=[malicious_shortcode]
2. Craft a payload to execute a shortcode from another plugin, e.g., [file_manager] or [admin_ajax].
3. Send the request:

   curl "http://target.com/?woocs=1&content=[wp-config-viewer]"
   

4. If successful, the shortcode output will be displayed in the response.

Example Payload:

curl -X POST "http://target.com/wp-admin/admin-ajax.php" \
  -d "action=woocs_ajax&content=[do_shortcode param='wp-config-viewer']"

Blue Team

Detection:

• Monitor for unusual shortcode names in HTTP requests to the plugin's endpoints.
• Look for patterns like content=[ in query strings or POST data.

Hunting:

• Search logs for requests containing woocs parameter with shortcode syntax.
• Use the following Splunk query:

  index=web sourcetype=access_combined uri=*woocs* | search "content=[" 
  

Lab Setup:

• Install WordPress 6.5 with FOX Currency Switcher 1.4.1.8.
• Install a test plugin that registers a harmless shortcode (e.g., [test_shortcode]).
• Verify the vulnerability by accessing http://lab/?woocs=1&content=[test_shortcode].

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests containing woocs parameter with shortcode syntax (e.g., content=[malicious]).
  • Unusual shortcode names in POST data to admin-ajax.php with action=woocs_ajax.

• File IOCs:

  • Modified .htaccess files (if shortcode allows file manipulation).
  • Unexpected files in wp-content/uploads/ (if shortcode allows file upload).

• Log IOCs:

  • Repeated 200 responses to /?woocs=1&content=... from different IPs.
  • Error logs showing do_shortcode() calls with unexpected parameters.

Detection Engineering

YARA Rule

rule CVE_2024_3734_Shortcode_Exploit {
    meta:
        description = "Detects exploitation attempts of CVE-2024-3734 in FOX Currency Switcher"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-3734"
    strings:
        $shortcode_param = "woocs" nocase
        $content_param = "content=" nocase
        $shortcode_pattern = /content=\[.*\]/ nocase
    condition:
        $shortcode_param and $content_param and $shortcode_pattern
}

Sigma Rule

title: CVE-2024-3734 FOX Currency Switcher Shortcode Exploit
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP requests attempting to exploit CVE-2024-3734 via arbitrary shortcode execution
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: 
            - 'woocs'
            - 'content=['
    condition: selection
falsepositives:
    - Legitimate use of the plugin's shortcode feature (rare)
level: high

Suricata Rule

alert http any any -> any any (
    msg:"CVE-2024-3734 FOX Currency Switcher Shortcode Exploit Attempt";
    flow:to_server,established;
    content:"woocs"; http_uri; nocase;
    content:"content=["; http_uri; nocase;
    pcre:"/content=\[.*\]/Ui";
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
    reference:url,https://nvd.nist.gov/vuln/detail/CVE-2024-3734;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Implement a Web Application Firewall (WAF) rule to block requests containing woocs and content=[ patterns.
3. Restrict shortcode execution by adding a custom filter in functions.php:

   add_filter('do_shortcode_tag', function($output, $tag, $attr, $m) {
       if ($tag === 'woocs') {
           // Whitelist allowed shortcodes
           $allowed = array('woocs', 'woocs_converter');
           if (!in_array($m[0], $allowed)) {
               return '';
           }
       }
       return $output;
   }, 10, 4);
   

Long-term Fix:

• Monitor the vendor's website for a patched version (>= 1.4.1.9).
• Consider switching to an alternative currency switcher plugin with better security practices.

Valters IT – Securing digital frontiers, one CVE at a time.