CVE-2026-4987: SureForms Payment Bypass Vulnerability

CVE-2026-4987 Overview

The SureForms – Contact Form, Payment Form & Other Custom Form Builder plugin for WordPress contains a Payment Amount Bypass vulnerability affecting all versions up to and including 2.5.2. This improper input validation flaw exists in the create_payment_intent() function, which performs payment validation solely based on a user-controlled parameter. Unauthenticated attackers can exploit this weakness to bypass configured form payment-amount validation and create underpriced payment or subscription intents by setting the form_id parameter to 0.

Critical Impact

Attackers can manipulate payment amounts without authentication, potentially leading to significant financial losses for businesses relying on SureForms for payment processing.

Affected Products

• SureForms – Contact Form, Payment Form & Other Custom Form Builder plugin for WordPress versions ≤ 2.5.2

Discovery Timeline

• 2026-03-28 - CVE CVE-2026-4987 published to NVD
• 2026-03-30 - Last updated in NVD database

Technical Details for CVE-2026-4987

Vulnerability Analysis

This vulnerability stems from CWE-20 (Improper Input Validation) in the SureForms WordPress plugin's payment processing logic. The create_payment_intent() function fails to properly validate payment amounts against server-side configurations, instead relying on client-controlled input to determine the payment value. This architectural flaw allows attackers to manipulate the payment flow by providing unexpected parameter values.

The vulnerability is particularly concerning because it requires no authentication to exploit. An attacker can submit crafted requests directly to the WordPress AJAX handler responsible for payment intent creation. By setting the form_id parameter to 0, the function bypasses the normal validation logic that would enforce the configured payment amount, allowing the attacker to specify an arbitrary (lower) amount.

Root Cause

The root cause is improper input validation in the create_payment_intent() function. The function performs payment validation solely based on the value of a user-controlled parameter without verifying it against server-side payment configurations. When the form_id is set to 0 or an invalid value, the validation logic fails to enforce the expected payment amount constraints, defaulting to accepting whatever amount the attacker specifies.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability remotely by:

1. Identifying a WordPress site using the vulnerable SureForms plugin with payment functionality enabled
2. Intercepting or crafting payment form submissions
3. Modifying the form_id parameter to 0 in the request to the create_payment_intent() endpoint
4. Submitting an arbitrary payment amount, bypassing the form's configured price validation
5. Completing the payment at the manipulated (underpriced) amount

This allows attackers to purchase products, services, or subscriptions at significantly reduced prices, causing direct financial harm to the website owner.

Detection Methods for CVE-2026-4987

Indicators of Compromise

• Unexpected payment intents with amounts significantly lower than configured prices
• Payment transactions with form_id values of 0 or other invalid identifiers
• Anomalous AJAX requests to WordPress endpoints with manipulated payment parameters
• Discrepancies between expected revenue and actual payment processor records

Detection Strategies

• Monitor WordPress AJAX logs for requests to payment-related endpoints with suspicious form_id values
• Implement application-layer logging to track all payment intent creation requests
• Configure payment processor webhooks to alert on transactions below expected minimum amounts
• Review SureForms payment logs for patterns indicating parameter manipulation

Monitoring Recommendations

• Set up alerts for payment transactions that deviate significantly from configured form amounts
• Implement real-time monitoring of WordPress AJAX endpoints handling payment processing
• Cross-reference payment processor records with WordPress plugin logs to identify discrepancies
• Configure web application firewall rules to flag requests with form_id=0 to payment endpoints

How to Mitigate CVE-2026-4987

Immediate Actions Required

• Update the SureForms plugin to a version newer than 2.5.2 that includes the security patch
• Review recent payment transactions for any suspicious activity or underpriced payments
• Temporarily disable payment functionality in SureForms if an immediate update is not possible
• Implement web application firewall rules to block requests with form_id=0 to payment endpoints

Patch Information

The vulnerability has been addressed in the official SureForms plugin repository. The security fix can be reviewed in the WordPress Plugin Changeset. Website administrators should update to the latest version of SureForms through the WordPress plugin update mechanism. For additional technical details and vulnerability analysis, refer to the Wordfence Vulnerability Report.

Workarounds

• Disable the SureForms payment functionality until the plugin can be updated
• Implement server-side validation in a custom WordPress hook to verify payment amounts before processing
• Use a web application firewall to filter and block suspicious payment requests with invalid form_id values
• Consider temporarily switching to an alternative payment solution until the vulnerability is patched