CVE-2024-54356

Executive Summary

CVE-2024-54356 is a Cross-Site Request Forgery (CSRF) vulnerability in the Vcita Online Booking & Scheduling Calendar plugin for WordPress (meeting-scheduler-by-vcita). This vulnerability affects all versions up to and including 4.5. A successful CSRF attack can trick an authenticated administrator into performing unintended actions, such as modifying plugin settings or creating unauthorized bookings, without their knowledge. The vulnerability is classified as a WordPress ecosystem issue, as it resides within the plugin's codebase and does not involve the underlying web server (Apache/Nginx). No public exploit code or proof-of-concept is currently available, and the patch status remains unknown.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The plugin is distributed via the official WordPress plugin repository and is also available for direct download from the vendor's site. Users should verify the integrity of the plugin files by checking checksums provided by the vendor or WordPress.org. No known supply chain compromise has been reported for this plugin.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
• Base Score: 5.4 (Medium)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

The threat level is considered Medium due to the requirement for user interaction (e.g., clicking a malicious link) and the limited impact on confidentiality and integrity. However, the vulnerability could be chained with other attacks to escalate privileges or exfiltrate data.

Deep Dive & Mechanics

The CSRF vulnerability exists because the plugin fails to implement proper nonce validation or other anti-CSRF tokens on state-changing requests. An attacker can craft a malicious HTML page or email that, when viewed by an authenticated WordPress administrator, triggers a forged request to the plugin's admin endpoints. This could allow the attacker to:

• Modify plugin settings (e.g., change booking availability, alter notification emails).
• Create, modify, or delete bookings.
• Potentially inject malicious JavaScript if the plugin stores unsanitized input (though this is not confirmed).

The attack requires the victim to be logged into WordPress and to interact with the malicious payload (e.g., by clicking a link or viewing an image). The request is sent with the victim's session cookies, making it appear legitimate to the server.

Vulnerable vs. Patched Code

Since no patch is available, a comparison cannot be made. However, a secure implementation would include:

• Nonce verification: Use WordPress's wp_nonce_field() and check_admin_referrer() functions on all admin forms and AJAX handlers.
• Referrer header checking: Validate the Referer header to ensure requests originate from the same site.
• SameSite cookie attribute: Set cookies with SameSite=Lax or SameSite=Strict to prevent cross-site requests from including cookies.

Vulnerable code example (hypothetical):

// No nonce check
if (isset($_POST['update_settings'])) {
    update_option('vcita_settings', $_POST['settings']);
}

Patched code example (hypothetical):

if (isset($_POST['update_settings']) && wp_verify_nonce($_POST['_wpnonce'], 'vcita_settings_nonce')) {
    update_option('vcita_settings', $_POST['settings']);
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• A WordPress site with the vulnerable plugin installed and an authenticated admin session.
• A malicious HTML page hosted on an attacker-controlled server.

Exploitation Steps:

1. Craft a malicious HTML page that automatically submits a form to the vulnerable endpoint:

   <html>
   <body>
   <form action="http://target-site.com/wp-admin/admin-post.php?action=vcita_update_settings" method="POST">
       <input type="hidden" name="vcita_option" value="malicious_value" />
       <input type="submit" value="Click me" />
   </form>
   <script>document.forms[0].submit();</script>
   </body>
   </html>
   

2. Host the page and send the link to the victim (e.g., via email or social engineering).
3. When the victim (authenticated admin) visits the page, the form is submitted automatically, modifying the plugin settings.

Note: No public exploit code is available; the above is a generic CSRF example.

Blue Team

Detection & Prevention:

• Monitor for unusual POST requests to /wp-admin/admin-post.php with action parameters related to vcita.
• Implement Web Application Firewall (WAF) rules to block requests missing a valid nonce.
• Educate administrators about phishing attacks and the importance of logging out after admin sessions.
• Use browser extensions that block cross-site requests (e.g., uMatrix).

Indicators of Compromise (IOCs)

• Network IOCs:
  • Suspicious POST requests to /wp-admin/admin-post.php with action=vcita_* parameters.
  • Referrer headers from external domains (e.g., attacker-controlled sites).
• File IOCs:
  • Modified plugin settings in the WordPress database (e.g., wp_options table with vcita_* keys).
• Log IOCs:
  • Unusual admin actions logged in WordPress audit logs (if available).

Detection Engineering

YARA Rule

rule detect_vcita_csrf_exploit {
    meta:
        description = "Detects CSRF exploit attempts against Vcita plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-54356"
    strings:
        $action = "action=vcita_" nocase
        $post = "POST" nocase
        $admin_post = "/wp-admin/admin-post.php" nocase
    condition:
        all of them
}

Sigma Rule

title: Vcita CSRF Exploit Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects CSRF attempts against Vcita plugin
author: Valters IT
date: 2025-04-10
references:
    - CVE-2024-54356
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: POST
        cs-uri-query|contains: "action=vcita_"
        cs-uri-stem|endswith: "/wp-admin/admin-post.php"
    condition: selection
falsepositives:
    - Legitimate admin actions
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-54356 Vcita CSRF Exploit Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-post.php"; http_uri; content:"action=vcita_"; http_uri; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released by the vendor.
2. Implement a Web Application Firewall (WAF) rule to block requests to /wp-admin/admin-post.php that do not contain a valid nonce.
3. Enforce strong session management by setting SameSite=Lax or SameSite=Strict on WordPress cookies.

Long-term Fix:

• The vendor must release a patched version that includes proper CSRF protection (nonce validation, referrer checking).
• Users should update to the latest version as soon as it becomes available.

Workarounds:

• Use a security plugin (e.g., Wordfence, Sucuri) that adds CSRF protection to admin actions.
• Restrict admin access to trusted IP addresses only.

Valters IT