The SureForms – Contact Form, Payment Form & Other Custom Form Builder plugin for WordPress suffers from a critical input validation vulnerability (CWE-20) identified as CVE-2026-4987. The vulnerability arises from the create_payment_intent() function, which performs payment amount validation based solely on the value of a user-controlled parameter, form_id. Attackers can exploit this by setting form_id to 0, bypassing the configured payment amount validation checks. This allows them to create payment or subscription intents with underpriced amounts, effectively paying less than the intended price. The vulnerability affects all versions up to and including 2.5.2 of the plugin. It requires no authentication or user interaction, making it remotely exploitable over the network. The flaw compromises the integrity of payment processing, potentially leading to financial losses for merchants using the plugin. Although no public exploits are currently known, the vulnerability's nature and ease of exploitation make it a significant threat. The CVSS v3.1 base score is 7.5, indicating high severity with a network attack vector, low attack complexity, no privileges required, no user interaction, and an impact limited to integrity. The vulnerability is categorized under CWE-20, highlighting improper input validation as the root cause. No official patches or updates have been linked yet, so mitigation strategies must be implemented promptly to reduce risk.

The primary impact of CVE-2026-4987 is financial loss due to unauthorized payment amount manipulation. Attackers can exploit this vulnerability to pay less than the required amount for goods or services, undermining the revenue of organizations using the SureForms plugin for payment processing. This compromises the integrity of payment transactions and can damage trust between merchants and customers. Additionally, widespread exploitation could lead to reputational damage and potential legal liabilities for failing to secure payment systems. Since the vulnerability requires no authentication and can be exploited remotely, the attack surface is broad, affecting any website using the vulnerable plugin version. The availability and confidentiality of systems are not directly impacted; however, the integrity breach is significant. Organizations relying on SureForms for subscription or payment forms are particularly at risk, especially those with high transaction volumes or critical financial operations.

1. Immediately update the SureForms plugin to a patched version once it becomes available from Brainstormforce. Monitor official channels for release announcements. 2. In the absence of an official patch, implement server-side validation to verify payment amounts independently of user-controlled parameters before processing payments. 3. Restrict or sanitize the form_id parameter to prevent it from being set to invalid values such as 0. 4. Employ Web Application Firewalls (WAFs) with custom rules to detect and block requests attempting to manipulate form_id or create underpriced payment intents. 5. Monitor payment transactions for anomalies such as unusually low payment amounts or repeated attempts to bypass payment validation. 6. Conduct regular security audits and penetration testing focused on payment processing workflows. 7. Educate development and operations teams about the vulnerability and ensure secure coding practices to avoid similar input validation issues. 8. Consider implementing multi-factor verification for payment submissions or integrating third-party payment gateways with robust validation mechanisms as an additional layer of defense.