CVE-2026-16025 in PayTR Virtual Pos iFrame API Plugin
Summary
by MITRE • 09/08/2026
Improper validation of specified quantity in input vulnerability in PayTR Payment and Electronic Money Institution Inc. PayTR Virtual Pos iFrame API (v9x) WHMCS Module allows Input Data Manipulation.
This issue affects PayTR Virtual Pos iFrame API (v9x) WHMCS Module: from v9.0.0 before v9.0.3.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability identified in the PayTR Virtual Pos iFrame API within the WHMCS module versions 9.0.0 through 9.0.2 represents a critical flaw in input validation logic, specifically concerning the handling of transaction quantities or monetary amounts. As an integration layer between the WHMCS billing platform and the PayTR payment gateway, this module is responsible for securely transmitting financial data to facilitate electronic money transactions. The core technical deficiency lies in the insufficient sanitization and type checking of user-supplied input fields that dictate the quantity or value of a transaction before it is processed by the backend API. This lack of rigorous validation allows an attacker to manipulate these parameters, potentially altering the intended financial outcome of a purchase without authorization from the legitimate account holder or merchant system logic.
From a technical perspective, this flaw aligns with CWE-20 Improper Input Validation and more specifically CWE-74 Injection in certain contexts where unsanitized data influences control flow or database queries related to transaction records. The vulnerability enables what is known as input data manipulation, allowing malicious actors to modify the payload sent during the checkout process. By intercepting and altering HTTP requests associated with the iFrame API calls, an attacker can change parameters such as item quantity, unit price, or total amount. This capability undermines the integrity of the financial transaction pipeline, as the system trusts these inputs without verifying their consistency against expected business rules or database-stored values for the products being purchased.
The operational impact of this vulnerability is severe due to its direct association with financial systems and electronic money institutions. Successful exploitation could lead to unauthorized transactions where a user pays significantly less than the actual cost, effectively stealing goods or services from merchants through price manipulation. Conversely, if the logic allows overcharging, it constitutes fraud against customers. Furthermore, because WHMCS is widely used by hosting providers and digital service vendors, this vulnerability poses a systemic risk across multiple businesses that rely on automated billing processes. The integrity of financial records can be compromised, leading to revenue loss for merchants and potential legal liabilities related to fraudulent activity processing.
In the context of cybersecurity frameworks, this issue reflects weaknesses in the ATT&CK technique T1589 Gather Victim Identity Information if used as a precursor step, but more directly maps to T1496 Resource Hijacking or financial fraud vectors where system resources are exploited for unauthorized gain. The lack of server-side validation means that client-side controls can be easily bypassed using standard web proxy tools like Burp Suite or OWASP ZAP. This highlights the fundamental security principle that all input must be treated as untrusted, regardless of its source within a trusted application interface.
To mitigate this vulnerability, immediate action is required to upgrade the PayTR Virtual Pos iFrame API WHMCS module to version 9.0.3 or later, where these validation checks have been corrected. In addition to upgrading, organizations should implement robust server-side validation for all financial parameters before they are passed to external payment gateways. This includes verifying that the transaction amount matches the sum of line items stored in the local database rather than relying solely on values submitted by the client browser. Implementing strict type checking and range validation ensures that only expected integer or decimal formats are accepted, preventing injection attacks and data manipulation attempts. Regular security audits and penetration testing focused on payment flows are also recommended to identify similar weaknesses in other integrated systems.