CVE-2025-26926

Executive Summary

CVE-2025-26926 is a Cross-Site Request Forgery (CSRF) vulnerability affecting the Booknetic WordPress plugin by fs-code, up to and including version 4.0.9. This vulnerability allows an attacker to trick an authenticated administrator into performing unintended actions, such as modifying plugin settings or creating unauthorized bookings, without their consent. The attack requires user interaction (clicking a crafted link) and has a CVSS v3.1 base score of 4.3 (Medium). As of this report, no official patch has been released, and no public proof-of-concept (PoC) code is available. The vulnerability is classified under CWE-352.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository and third-party marketplaces. Users are advised to monitor the plugin’s update channel and apply patches as soon as they become available. Since no patch exists, temporary mitigations (e.g., CSRF tokens, nonce validation) should be implemented manually or via a Web Application Firewall (WAF).

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
• Base Score: 4.3 (Medium)
• Attack Vector (AV): Network – The attack can be launched remotely.
• Attack Complexity (AC): Low – No special conditions required.
• Privileges Required (PR): None – The attacker does not need authentication.
• User Interaction (UI): Required – The victim must click a malicious link or visit a crafted page.
• Scope (S): Unchanged – The vulnerable component and the attacker’s target are the same.
• Confidentiality (C): None – No data exposure.
• Integrity (I): Low – Attacker can modify plugin settings or data.
• Availability (A): None – No denial of service.

Threat Level: Medium. Exploitation requires social engineering, but the impact on integrity (e.g., changing booking configurations) could lead to further attacks.

Deep Dive & Mechanics

The Booknetic plugin fails to implement proper CSRF protection (nonce tokens) on sensitive administrative actions. An attacker can craft a malicious HTML page or email that, when visited by an authenticated WordPress admin, triggers a forged request to the Booknetic backend. This could allow the attacker to:

• Modify plugin settings (e.g., change booking times, prices, or user roles).
• Create, delete, or modify bookings.
• Disable security features within the plugin.

The vulnerability exists because the plugin does not validate the origin of requests or include a CSRF token in forms/AJAX calls. Since WordPress core provides a nonce API, this is a clear oversight by the developer.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be in the plugin’s admin AJAX handlers. A patched version would include nonce verification using check_ajax_referer() or wp_verify_nonce().

Vulnerable Code Example (hypothetical):

add_action('wp_ajax_booknetic_save_settings', 'booknetic_save_settings');
function booknetic_save_settings() {
    // No nonce check
    update_option('booknetic_settings', $_POST['settings']);
    wp_die();
}

Patched Code Example:

add_action('wp_ajax_booknetic_save_settings', 'booknetic_save_settings');
function booknetic_save_settings() {
    check_ajax_referer('booknetic_nonce', 'nonce');
    update_option('booknetic_settings', $_POST['settings']);
    wp_die();
}

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• A WordPress site with Booknetic <= 4.0.9 installed and an authenticated admin session.
• Attacker-controlled web server or email delivery.

Exploitation Steps:

1. Identify a sensitive action endpoint (e.g., /wp-admin/admin-ajax.php?action=booknetic_save_settings).
2. Craft a malicious HTML page that auto-submits a form to that endpoint with attacker-controlled parameters.
3. Host the page and send the link to the victim admin via email or social engineering.
4. When the admin visits the page while logged into WordPress, the forged request executes.

Example Malicious HTML:

<html>
<body>
<form action="http://target-site.com/wp-admin/admin-ajax.php" method="POST">
  <input type="hidden" name="action" value="booknetic_save_settings">
  <input type="hidden" name="settings[booking_price]" value="0.01">
  <input type="submit" value="Click me">
</form>
<script>document.forms[0].submit();</script>
</body>
</html>

Blue Team (Defense & Detection)

Detection:

• Monitor for unexpected changes to Booknetic settings or bookings.
• Look for suspicious referrer headers or unusual POST requests to admin-ajax.php with action=booknetic_* parameters.
• Use a WAF to block requests missing a valid nonce token.

Mitigation:

• Apply a virtual patch via WAF rules (e.g., ModSecurity) to require a nonce parameter.
• Disable the plugin until an official patch is released.
• Educate administrators about phishing attacks.

Indicators of Compromise (IOCs)

• Network:
  • POST requests to /wp-admin/admin-ajax.php with action=booknetic_* and no nonce parameter.
  • Referrer header from an external domain (e.g., attacker-controlled site).
• Host:
  • Unexpected changes in wp_options table (e.g., booknetic_settings).
  • New or modified bookings in the booknetic_bookings table.
• Logs:
  • WordPress debug log entries showing failed nonce checks (if patched).
  • Web server access logs with unusual POST requests to admin-ajax.php.

Detection Engineering

YARA Rule

rule CVE_2025_26926_Booknetic_CSRF {
    meta:
        description = "Detects Booknetic plugin files vulnerable to CSRF (CVE-2025-26926)"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-26926"
    strings:
        $ajax_handler = /add_action\s*\(\s*['\"]wp_ajax_booknetic_/
        $no_nonce = /check_ajax_referer|wp_verify_nonce/
    condition:
        $ajax_handler and not $no_nonce
}

Sigma Rule

title: CVE-2025-26926 Booknetic CSRF Exploitation Attempt
id: 8a3f7c2e-5b1d-4a9f-8c6e-2d1f3a4b5c6d
status: experimental
description: Detects POST requests to WordPress admin-ajax.php with Booknetic actions lacking nonce
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: accesslog
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'action=booknetic_'
        cs-uri-query|contains: 'admin-ajax.php'
    filter:
        cs-uri-query|contains: 'nonce='
    condition: selection and not filter
falsepositives:
    - Legitimate plugin updates with nonce (if patched)
level: high

Suricata Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"CVE-2025-26926 Booknetic CSRF Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=booknetic_"; http_client_body; pcre:"/nonce=/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Booknetic plugin until an official patch is released.
2. Implement a virtual patch using a WAF (e.g., Cloudflare, ModSecurity) to block requests to admin-ajax.php with action=booknetic_* that lack a valid nonce.
3. Educate administrators about CSRF risks and phishing attacks.

Long-term Fix:

• The vendor (fs-code) must release a patched version that includes nonce verification on all AJAX actions. Users should update to the latest version as soon as it becomes available.

Workaround:

• Add a custom plugin or mu-plugin that enforces nonce checks for Booknetic actions:

add_action('wp_ajax_booknetic_save_settings', 'custom_booknetic_nonce_check', 1);
function custom_booknetic_nonce_check() {
    if (!check_ajax_referer('booknetic_nonce', 'nonce', false)) {
        wp_die('CSRF detected');
    }
}

Valters IT
Securing Digital Frontiers