CVE-2023-6242

Executive Summary

CVE-2023-6242 is a Cross-Site Request Forgery (CSRF) vulnerability affecting the EventON WordPress plugin (both Pro and Free versions). The flaw resides in the evo_eventpost_update_meta function, which lacks proper nonce validation. This allows an unauthenticated attacker to forge requests that update arbitrary post metadata, provided they can trick a site administrator into performing an action (e.g., clicking a malicious link). The CVSS score is 6.5 (Medium), with a vector emphasizing network attack vector, low attack complexity, no privileges required, but user interaction is required. The impact is limited to integrity (no confidentiality or availability impact). No public proof-of-concept or exploit code is available, and the patch status remains unknown.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The EventON plugin is distributed via the WordPress Plugin Directory and third-party marketplaces. Users should verify the integrity of their plugin files and ensure they are obtained from trusted sources. No known supply chain compromise has been reported.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
• Attack Vector (AV): Network – the attack can be launched remotely.
• Attack Complexity (AC): Low – no special conditions required.
• Privileges Required (PR): None – attacker does not need authentication.
• User Interaction (UI): Required – victim must click a link or perform an action.
• Scope (S): Unchanged – the vulnerable component is the plugin itself.
• Confidentiality (C): None – no data exposure.
• Integrity (I): High – attacker can modify arbitrary post metadata.
• Availability (A): None – no denial of service.

Threat Level: Medium. While the impact is limited to integrity, the ability to modify post metadata could lead to defacement, injection of malicious content, or manipulation of event data.

Deep Dive & Mechanics

The vulnerability is a classic CSRF in the WordPress plugin EventON. The function evo_eventpost_update_meta is responsible for updating custom post metadata for events. In vulnerable versions, this function does not verify a nonce (a one-time token) to ensure the request originated from the legitimate admin interface. As a result, an attacker can craft a malicious HTML page or link that, when visited by an authenticated administrator, triggers a POST request to the WordPress admin-ajax endpoint with the necessary parameters to update post metadata.

The attack flow:

1. Attacker identifies a target WordPress site running a vulnerable EventON version.
2. Attacker crafts a malicious link or embeds a form in a page that auto-submits to wp-admin/admin-ajax.php with action evo_eventpost_update_meta and desired post ID and metadata.
3. Attacker lures an administrator to click the link or visit the page.
4. The administrator’s browser sends the forged request, including their session cookies.
5. The plugin processes the request without nonce validation, updating the post metadata.

The vulnerability affects both the Pro version (up to 4.5.4) and the Free version (up to 2.2.7). No patch has been released as of the latest advisory.

Vulnerable vs. Patched Code

The vulnerable code is in the evo_eventpost_update_meta function. A typical vulnerable implementation might look like:

// Vulnerable code (no nonce check)
function evo_eventpost_update_meta() {
    $post_id = $_POST['post_id'];
    $meta_key = $_POST['meta_key'];
    $meta_value = $_POST['meta_value'];
    update_post_meta($post_id, $meta_key, $meta_value);
    wp_die();
}
add_action('wp_ajax_evo_eventpost_update_meta', 'evo_eventpost_update_meta');

A patched version would include a nonce verification:

// Patched code (with nonce check)
function evo_eventpost_update_meta() {
    if ( ! isset( $_POST['_wpnonce'] ) || ! wp_verify_nonce( $_POST['_wpnonce'], 'evo_eventpost_update_meta_nonce' ) ) {
        wp_die( 'Security check failed.' );
    }
    $post_id = $_POST['post_id'];
    $meta_key = $_POST['meta_key'];
    $meta_value = $_POST['meta_value'];
    update_post_meta($post_id, $meta_key, $meta_value);
    wp_die();
}
add_action('wp_ajax_evo_eventpost_update_meta', 'evo_eventpost_update_meta');

The key difference is the addition of wp_verify_nonce() to validate the request origin.

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• Target WordPress site with EventON plugin (vulnerable version).
• An authenticated administrator session (via social engineering).

Exploitation Steps:

1. Identify the target site and confirm the plugin version (e.g., via wp-content/plugins/eventon/readme.txt).
2. Craft a malicious HTML page that auto-submits a form to the target:

<html>
<body>
<form action="http://target-site.com/wp-admin/admin-ajax.php" method="POST" id="csrf-form">
    <input type="hidden" name="action" value="evo_eventpost_update_meta">
    <input type="hidden" name="post_id" value="123">
    <input type="hidden" name="meta_key" value="event_status">
    <input type="hidden" name="meta_value" value="cancelled">
</form>
<script>document.getElementById('csrf-form').submit();</script>
</body>
</html>

3. Host the page and send the link to the administrator (e.g., via email, social media).
4. Once the admin clicks, the metadata is updated without their knowledge.

Note: No public exploit code is available; this is a conceptual demonstration.

Blue Team (Defender)

Detection:

• Monitor for unusual POST requests to admin-ajax.php with action evo_eventpost_update_meta from non-admin IPs or without a valid nonce.
• Check server logs for referrer headers that do not match the admin dashboard URL.
• Use the detection rules provided below.

Hunting:

• Search for unauthorized changes to event post metadata, especially event_status, event_location, or custom fields.
• Review admin activity logs for unexpected metadata updates.

Indicators of Compromise (IOCs)

• Network:
  • POST requests to /wp-admin/admin-ajax.php with action=evo_eventpost_update_meta.
  • Referrer headers not matching the site’s admin URL (e.g., from external domains).
• Host:
  • Unexpected changes to wp_postmeta table entries for event posts.
  • Presence of malicious HTML files or iframes on the server (if attacker uploaded them).
• Logs:
  • Repeated admin-ajax.php calls from a single IP without corresponding admin login.
  • Error logs showing nonce verification failures (if patched).

Detection Engineering

YARA Rule

rule CVE_2023_6242_CSRF_EventON {
    meta:
        description = "Detects CSRF exploitation attempts against EventON plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-6242"
    strings:
        $ajax_action = "evo_eventpost_update_meta"
        $post_id = "post_id"
        $meta_key = "meta_key"
        $meta_value = "meta_value"
    condition:
        all of them
}

Sigma Rule

title: CSRF Exploitation Attempt Against EventON Plugin
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects POST requests to admin-ajax.php with action evo_eventpost_update_meta without proper nonce
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-query|contains: 'admin-ajax.php'
        cs-uri-query|contains: 'action=evo_eventpost_update_meta'
    condition: selection
falsepositives:
    - Legitimate admin actions (if nonce is present)
level: medium

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2023-6242 EventON CSRF Exploitation Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"admin-ajax.php"; http_uri;
    content:"action=evo_eventpost_update_meta"; http_client_body;
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
    reference:cve,2023-6242;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the EventON plugin until a patch is released.
2. Implement a Web Application Firewall (WAF) rule to block requests to admin-ajax.php with action=evo_eventpost_update_meta unless they include a valid nonce.
3. Educate administrators about phishing attacks and the risk of clicking unknown links.

Long-term Fix:

• Monitor the plugin vendor for a patched version (e.g., > 4.5.4 for Pro, > 2.2.7 for Free).
• Apply the patch as soon as it becomes available.
• Consider using a security plugin like Wordfence to add CSRF protection.

Workaround:

• Add a custom nonce check via a WordPress plugin or code snippet:

add_action('wp_ajax_evo_eventpost_update_meta', function() {
    if ( ! isset( $_POST['_wpnonce'] ) || ! wp_verify_nonce( $_POST['_wpnonce'], 'evo_eventpost_update_meta_nonce' ) ) {
        wp_die( 'CSRF detected.' );
    }
}, 1);

Valters IT
Securing Digital Frontiers