CVE-2025-67559

Executive Summary

CVE-2025-67559 identifies a Missing Authorization vulnerability in the Vcita Online Booking & Scheduling Calendar for WordPress plugin (slug: meeting-scheduler-by-vcita). This flaw allows an authenticated attacker (with low privileges) to exploit incorrectly configured access control security levels, potentially leading to unauthorized data access or modification of booking/scheduling settings. The vulnerability affects all versions up to and including 4.5.5. As of this report, no official patch has been released, and no public exploit code is available. The EPSS score is 0.0%, indicating a very low probability of active exploitation in the wild at this time.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress plugin repository. Users who installed the plugin directly from the WordPress dashboard or via the repository are affected. There is no known compromise of the plugin’s supply chain (e.g., malicious commits or backdoored packages). However, the lack of a patch means that all installations remain vulnerable until the vendor releases an update.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
• Base Score: 5.4 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: Low (PR:L) – attacker must have a valid WordPress user account (e.g., subscriber).
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: Low (C:L) – limited unauthorized data access.
• Integrity Impact: Low (I:L) – limited unauthorized modification.
• Availability Impact: None (A:N)

Threat Level: Medium. The vulnerability requires authentication, but low-privileged users (e.g., subscribers) can exploit it. The impact is limited to reading or modifying booking/scheduling data, not full site compromise.

Deep Dive & Mechanics

The vulnerability stems from Missing Authorization (CWE-862) in the plugin’s REST API endpoints or AJAX handlers. The plugin likely exposes functions that allow users to view or modify booking settings, appointments, or calendar data without properly checking if the current user has the required capabilities (e.g., manage_options or edit_posts).

Root Cause: The plugin fails to enforce capability checks on certain server-side actions. For example, a function like vcita_update_settings() might be hooked to wp_ajax_vcita_update_settings and only check for is_user_logged_in() instead of current_user_can('manage_options'). This allows any authenticated user, including subscribers, to call these endpoints.

Attack Vector:

1. An attacker registers or compromises a low-privileged WordPress account (e.g., subscriber).
2. The attacker crafts a POST request to the vulnerable AJAX endpoint (e.g., /wp-admin/admin-ajax.php?action=vcita_update_settings) with malicious parameters.
3. The server processes the request without verifying the user’s role, leading to unauthorized changes.

Potential Impact:

• Modify booking settings (e.g., change email notifications, alter time slots).
• Access other users’ appointment data.
• Delete or reschedule bookings.

Vulnerable vs. Patched Code

Since no patch is available, the following is a hypothetical comparison based on common missing authorization patterns.

Vulnerable Code (v4.5.5):

add_action('wp_ajax_vcita_update_settings', 'vcita_update_settings_callback');
function vcita_update_settings_callback() {
    // Missing capability check
    if (!is_user_logged_in()) {
        wp_die('Unauthorized');
    }
    // Process and save settings
    update_option('vcita_settings', $_POST['settings']);
    wp_send_json_success();
}

Patched Code (Hypothetical):

add_action('wp_ajax_vcita_update_settings', 'vcita_update_settings_callback');
function vcita_update_settings_callback() {
    // Proper capability check
    if (!current_user_can('manage_options')) {
        wp_die('Unauthorized');
    }
    // Nonce verification
    if (!wp_verify_nonce($_POST['_wpnonce'], 'vcita_update_settings')) {
        wp_die('Nonce verification failed');
    }
    // Process and save settings
    update_option('vcita_settings', sanitize_text_field($_POST['settings']));
    wp_send_json_success();
}

Exploitation & Lab Setup

Red Team (Proof of Concept)

Prerequisites:

• A WordPress site with Vcita plugin <= 4.5.5 installed.
• A low-privileged user account (e.g., subscriber).

Exploitation Steps:

1. Log in as the low-privileged user and obtain a valid WordPress nonce (if required) by inspecting the page source or using browser developer tools.
2. Craft a POST request to the vulnerable AJAX endpoint using curl or a tool like Burp Suite.

curl -X POST \
  'http://target.com/wp-admin/admin-ajax.php' \
  -H 'Content-Type: application/x-www-form-urlencoded' \
  -d 'action=vcita_update_settings&_wpnonce=VALID_NONCE&settings[email]=attacker@evil.com'

3. Verify the change by checking the plugin’s settings page or observing altered behavior (e.g., booking notifications sent to attacker’s email).

Note: No public exploit code exists. The above is a generic example based on common patterns.

Blue Team (Detection & Hardening)

Detection:

• Monitor AJAX requests to admin-ajax.php with actions containing vcita_ from low-privileged users.
• Look for unusual changes to the wp_options table where option_name contains vcita.

Hardening:

• Apply the principle of least privilege: ensure only administrators can modify plugin settings.
• Use a Web Application Firewall (WAF) to block suspicious AJAX requests.
• Temporarily disable the plugin until a patch is released.

Indicators of Compromise (IOCs)

• Network IOCs:
  • POST requests to /wp-admin/admin-ajax.php with action=vcita_* from non-admin users.
  • Unusual Referer headers or missing nonce parameters.
• File IOCs:
  • Modified wp_options entries: option_name like vcita_settings with unexpected values.
• Log IOCs:
  • WordPress debug log entries showing wp_ajax_vcita_* calls from user roles other than administrator.

Detection Engineering

YARA Rule

rule Detect_Vcita_Missing_Auth_Exploit {
    meta:
        description = "Detects exploitation attempts of CVE-2025-67559 in Vcita plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-67559"
    strings:
        $ajax_action = "action=vcita_" nocase
        $admin_ajax = "admin-ajax.php" nocase
        $post_method = "POST" nocase
    condition:
        $ajax_action and $admin_ajax and $post_method
}

Sigma Rule

title: Vcita Missing Authorization Exploitation Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects attempts to exploit CVE-2025-67559 by sending AJAX requests to Vcita endpoints from low-privileged users.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'admin-ajax.php'
        cs-uri-query|contains|all:
            - 'action=vcita_'
            - 'vcita_update_settings'
    condition: selection
falsepositives:
    - Legitimate admin actions (rare)
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-67559 Vcita Missing Authorization Exploit"; flow:to_server,established; content:"POST"; http_method; content:"admin-ajax.php"; http_uri; content:"action=vcita_"; http_client_body; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released by the vendor.
2. Restrict user roles: Ensure only trusted administrators have access to the site.
3. Monitor logs for suspicious AJAX requests targeting Vcita endpoints.

Long-Term Fix:

• The vendor must release a patched version (>= 4.5.6) that includes proper capability checks (current_user_can('manage_options')) and nonce verification.
• Users should update the plugin as soon as the patch is available.

Workaround:

• Implement a custom function in the theme’s functions.php to block unauthorized AJAX calls:

add_action('wp_ajax_vcita_update_settings', function() {
    if (!current_user_can('manage_options')) {
        wp_die('Unauthorized');
    }
}, 1);

Valters IT