CVE-2026-103331 in UniPAY Payment Gateway for WooCommerce Plugin
Summary
by MITRE • 10/28/2026
The UniPAY Payment Gateway For WooCommerce WordPress plugin through 2.3 does not properly verify the authenticity of payment notifications, as their signature is checked against a merchant secret that is empty by default, allowing unauthenticated attackers to forge a valid notification and mark arbitrary orders as paid.
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Analysis
by VulDB Data Team • 10/28/2026
The vulnerability identified in UniPAY Payment Gateway for WooCommerce versions up to 2.3 represents a critical failure in authentication logic within the payment processing workflow of WordPress-based e-commerce sites. This flaw specifically affects how the plugin validates incoming payment notifications, commonly referred to as webhooks or IPNs (Instant Payment Notifications), from external payment processors. The core technical deficiency lies in the verification mechanism for digital signatures used to ensure message integrity and authenticity. Instead of relying on a securely generated cryptographic key shared between the merchant's server and the payment gateway, the system defaults to an empty string for the secret key used in signature validation. This configuration error effectively disables the authentication check entirely under default installation conditions, creating a severe security gap that attackers can exploit without needing valid credentials or prior access to the target environment.
From a technical perspective, this vulnerability is classified as CWE-287: Improper Authentication and CWE-345: Insufficient Verification of Data Authenticity. The plugin's code attempts to verify the signature of incoming payment data by comparing it against a merchant secret stored in its configuration settings. However, because this field is left blank during initial setup or if not explicitly configured by the administrator, the cryptographic comparison operation fails to enforce any security constraints. In many programming contexts, an empty key may result in a hash that matches any input or causes the verification function to return true erroneously due to lack of strict equality checks against a non-existent baseline. Consequently, any actor on the internet can construct a malicious HTTP POST request containing fabricated payment data and submit it to the plugin's endpoint. Since the signature validation is bypassed via this default misconfiguration, the application accepts these forged notifications as legitimate transactions from trusted financial institutions.
The operational impact of this vulnerability is direct and financially significant for merchants using WooCommerce with UniPAY. An unauthenticated attacker can forge a payment notification that indicates an order has been successfully paid when it has not. This allows the attacker to complete fraudulent purchases without providing actual funds, leading to inventory loss, shipping costs incurred by the merchant, and potential chargeback liabilities if goods are shipped based on false confirmation. Furthermore, this exploit does not require any user interaction or social engineering; it can be automated using simple scripts targeting known endpoints associated with the plugin's webhook handling logic. The ease of exploitation means that even sites with strong general security postures remain vulnerable unless they specifically audit their payment gateway configurations for proper secret key management.
This incident aligns with MITRE ATT&CK technique T1496: Resource Hijacking or more accurately in this context, it relates to the broader category of Application Layer Attacks where an adversary manipulates application logic to achieve unauthorized outcomes. Specifically, it reflects patterns seen in CWE-829: Inclusion of Functionality from Untrusted Control Sector if one considers the payment gateway as a third-party service whose inputs are not properly sanitized or authenticated before processing business-critical state changes. The ability to mark arbitrary orders as paid constitutes an integrity violation that undermines the trust model of the e-commerce platform, allowing attackers to bypass financial controls entirely through input manipulation rather than exploiting software bugs in memory management or access control lists.
Mitigation strategies must focus on immediate configuration hardening and long-term architectural improvements. Administrators running affected versions should immediately update to a patched version if available from the plugin vendor. If an update is not yet released, the primary remediation step is to manually configure a strong, randomly generated secret key within the UniPAY settings in the WordPress admin dashboard before any further transactions are processed. This ensures that incoming notifications are validated against a known cryptographic baseline rather than an empty string. Additionally, merchants should implement server-side validation checks for payment statuses and consider adding additional layers of verification such as IP whitelisting if supported by their hosting environment or using secondary confirmation mechanisms like manual order review before shipping goods. Regular security audits of third-party plugins and adherence to secure coding standards that mandate non-empty secrets for cryptographic operations are essential preventive measures against similar vulnerabilities in the future.