CVE-2025-64261

Executive Summary

CVE-2025-64261 is a Missing Authorization vulnerability in the WordPress plugin Appointment Booking Calendar by CodePeople, affecting versions up to and including 1.3.95. 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. The vulnerability is classified as Medium Severity (CVSS 5.4) and currently has no known public exploit or patch. As a WordPress plugin vulnerability, it directly impacts the WordPress ecosystem and requires immediate attention from site administrators.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): Low (L) – Attacker needs a valid user account.
• User Interaction (UI): None (N) – No victim action needed.
• Scope (S): Unchanged (U) – Impact confined to the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited data modification.
• Availability (A): None (N) – No denial of service.

Threat Level: Medium. While the CVSS score is moderate, the lack of a patch and the potential for privilege escalation or data leakage in a WordPress environment elevates the risk for unpatched sites.

Deep Dive & Mechanics

The vulnerability resides in the Appointment Booking Calendar plugin's access control logic. The plugin fails to properly validate user capabilities when processing certain AJAX actions or REST API endpoints. Specifically, functions that should be restricted to administrators (e.g., managing appointments, viewing all bookings, modifying settings) are accessible to authenticated users with lower roles (e.g., subscribers, customers).

Root Cause: The plugin uses current_user_can() checks incorrectly or omits them entirely for certain operations. For example, a function like wp_ajax_abc_manage_appointments might only check if the user is logged in (is_user_logged_in()) rather than verifying a specific capability like manage_options.

Attack Vector: An attacker with a valid WordPress account (e.g., a subscriber) can craft HTTP requests to the vulnerable endpoints, bypassing intended access controls. This could allow them to:

• View all appointments (including other users' data).
• Modify appointment statuses.
• Access plugin settings.
• Potentially escalate privileges if combined with other flaws.

Vulnerable vs. Patched Code

Since no patch is available, we can only hypothesize the vulnerable pattern. A typical vulnerable code snippet in WordPress plugins looks like:

// VULNERABLE: Only checks if user is logged in
add_action('wp_ajax_abc_get_all_appointments', 'abc_get_all_appointments');
function abc_get_all_appointments() {
    if (!is_user_logged_in()) {
        wp_die('Unauthorized');
    }
    // Fetch and return all appointments without capability check
    $appointments = $wpdb->get_results("SELECT * FROM {$wpdb->prefix}abc_appointments");
    wp_send_json($appointments);
}

A patched version would include a proper capability check:

// PATCHED: Checks for 'manage_options' capability
add_action('wp_ajax_abc_get_all_appointments', 'abc_get_all_appointments');
function abc_get_all_appointments() {
    if (!current_user_can('manage_options')) {
        wp_die('Unauthorized');
    }
    // Fetch and return all appointments
    $appointments = $wpdb->get_results("SELECT * FROM {$wpdb->prefix}abc_appointments");
    wp_send_json($appointments);
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A WordPress site with Appointment Booking Calendar <= 1.3.95 installed.
• A valid low-privilege user account (e.g., subscriber).

Steps:

1. Log in as the low-privilege user and obtain a WordPress nonce (if required) by inspecting the page source or using browser developer tools.
2. Identify vulnerable endpoints by analyzing the plugin's AJAX hooks (e.g., wp_ajax_abc_get_all_appointments).
3. Craft a request using curl or a tool like Burp Suite:

curl -X POST 'https://target.com/wp-admin/admin-ajax.php' \
  --data 'action=abc_get_all_appointments&_wpnonce=YOUR_NONCE' \
  --cookie 'wordpress_logged_in_YOUR_COOKIE'

4. If successful, the response will contain sensitive appointment data.

Note: No public exploit code is available; this is a theoretical exploitation path.

Blue Team (Detection & Hardening)

Detection:

• Monitor for unusual AJAX requests from low-privilege users to admin-level actions.
• Look for patterns like action=abc_ followed by administrative functions (e.g., manage, settings, all).
• Use the Sigma rule below to detect unauthorized access attempts.

Hardening:

• Immediately disable or remove the plugin if no patch is available.
• Implement a Web Application Firewall (WAF) rule to block requests to known vulnerable endpoints from non-admin users.
• Restrict user roles and enforce the principle of least privilege.

Indicators of Compromise (IOCs)

• Network: HTTP POST requests to /wp-admin/admin-ajax.php with action parameters containing abc_ and administrative keywords (e.g., abc_get_all_appointments, abc_update_settings).
• Logs: WordPress debug logs showing failed capability checks or unexpected AJAX calls from low-privilege users.
• File: Modified plugin files (if attacker uploads malicious code) – check file integrity of /wp-content/plugins/appointment-booking-calendar/.

Detection Engineering

YARA Rule

rule Detect_Appointment_Booking_Calendar_Missing_Auth {
    meta:
        description = "Detects vulnerable Appointment Booking Calendar plugin files with missing authorization checks"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-64261"
    strings:
        $vuln_func = "is_user_logged_in()" nocase
        $admin_action = "wp_ajax_abc_" nocase
        $no_cap_check = "current_user_can" nocase
    condition:
        $admin_action and $vuln_func and not $no_cap_check
}

Sigma Rule

title: CVE-2025-64261 - Missing Authorization in Appointment Booking Calendar
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects unauthorized AJAX requests to vulnerable Appointment Booking Calendar endpoints
author: Valters IT
date: 2025/04/10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-64261
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/wp-admin/admin-ajax.php'
        cs-uri-query|contains: 'action=abc_'
    condition: selection
falsepositives:
    - Legitimate admin actions from authorized users
level: medium
tags:
    - attack.initial_access
    - attack.t1190

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-64261 - Appointment Booking Calendar Missing Authorization Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/wp-admin/admin-ajax.php"; http_uri;
    content:"action=abc_"; http_client_body;
    classtype:attempted-admin;
    sid:10000001;
    rev:1;
    reference:cve,2025-64261;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released by the vendor.
2. Review user roles and remove any unnecessary low-privilege accounts.
3. Monitor logs for suspicious AJAX activity using the provided Sigma rule.

Long-term:

• Subscribe to the vendor's security advisories for patch announcements.
• Implement a WordPress security plugin (e.g., Wordfence) to add virtual patching.
• Conduct a security audit of all installed plugins.

Note: Since no patch is available, the only guaranteed mitigation is to disable the plugin entirely.

Valters IT
Securing Digital Frontiers