CVE-2026-16990 in Payment Button for PayPal Plugin
Summary
by MITRE • 08/12/2026
The Payment Button for PayPal WordPress plugin through 1.2.3.44 does not enforce the merchant-configured price server-side and trusts a client-supplied payment amount, allowing unauthenticated attackers to create a real PayPal order against the merchant for an arbitrary lower amount.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/12/2026
This vulnerability exists in the Payment Button for PayPal WordPress plugin version 1.2.3.44 and earlier, representing a critical server-side validation flaw that undermines the integrity of payment processing workflows. The core issue stems from the plugin's failure to implement proper server-side price verification mechanisms, instead relying entirely on client-supplied payment amounts that are transmitted through the user interface. This design flaw creates an opportunity for attackers to manipulate payment values during transaction processing by directly modifying client-side parameters and submitting forged requests to the payment endpoint.
The technical implementation of this vulnerability demonstrates a classic lack of input validation and sanitization practices that violate fundamental security principles outlined in CWE-20, which addresses "Improper Input Validation." The plugin's architecture fails to establish proper server-side controls for verifying payment amounts against predefined merchant configurations, allowing attackers to bypass client-side validation entirely. This creates a scenario where malicious actors can submit payment requests with arbitrary lower amounts while maintaining the appearance of legitimate transactions through the PayPal integration framework.
The operational impact of this vulnerability extends beyond simple financial loss, as it enables attackers to conduct unauthorized payment processing activities that could compromise merchant trust and payment integrity. Unauthenticated attackers can exploit this flaw to create real PayPal orders for reduced amounts without requiring any authentication credentials or authorization tokens, effectively allowing them to perform unauthorized transactions against merchant accounts. This type of vulnerability directly impacts the principle of least privilege and violates security controls established in the OWASP Top Ten under A03:2021 - Injection, as it represents an injection attack vector that manipulates payment data flows.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1566.001 - Phishing: Email and represents a significant risk to merchants who rely on automated payment processing systems. The attack surface is particularly concerning given the widespread use of WordPress plugins and the typical trust placed in payment gateway integrations by both merchants and customers. The vulnerability allows attackers to exploit the trust relationship between PayPal and merchants, potentially enabling larger-scale fraud operations that could affect multiple merchant accounts simultaneously.
Mitigation strategies should focus on implementing robust server-side validation mechanisms that enforce merchant-configured prices through proper input sanitization and verification processes. Security controls must be implemented to ensure that all payment amounts are validated against predefined merchant configurations before processing, with no reliance on client-provided values for critical transaction parameters. Regular security audits and penetration testing should be conducted to identify similar validation flaws in other plugin components and core WordPress functionality. Additionally, merchants should implement monitoring systems to detect unusual payment patterns that could indicate exploitation of this vulnerability, while developers should establish secure coding practices that prioritize server-side validation over client-side trust mechanisms. The remediation approach should also consider implementing proper error handling and logging to track any attempts to manipulate payment values, ensuring compliance with PCI DSS requirements for payment transaction security.