CVE Alert: CVE-2026-16025 – PayTR Payment and Electronic Money Institution Inc. – PayTR Virtual Pos iFrame API (v9x) WHMCS Module

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.

High operational risk for exposed online shops, but current evidence does not indicate active exploitation; confirm KEV and EPSS status before final prioritisation.

An unauthorised remote attacker may be able to manipulate transaction-related input, potentially causing incorrect order totals, payment-flow disruption, refunds or fulfilment losses. The principal business risks are revenue leakage, customer disputes, reconciliation failures and loss of confidence in the checkout process. Availability impact could also affect sales during targeted or repeated attacks.

### Most likely attack path

The network-reachable, low-complexity path requires no privileges or customer interaction, so attackers could send crafted requests directly to the payment module or its checkout endpoints. Scope remains unchanged, limiting direct access to other security domains, but a compromised or disrupted payment component could still affect connected order, inventory and fulfilment workflows indirectly.

### Who is most exposed

Internet-facing WHMCS installations serving active online shops are the primary concern, particularly sites relying on this module for high-volume or high-value transactions. Shared hosting, weak monitoring and integrations with automated fulfilment increase the potential business impact.

Alert on abnormal payment quantities, totals or repeated validation failures.

Compare gateway confirmations with WHMCS order values and fulfilment records.

Review web-server and module logs for unauthenticated requests to checkout/payment endpoints.

Hunt for bursts of requests from a source, ASN or user agent across multiple shops.

Monitor refunds, cancellations and payment discrepancies following suspicious traffic.

### Mitigation and prioritisation

Apply the vendor’s fixed release promptly; treat as high-priority maintenance for internet-facing shops.

Add server-side allow-listing, rate limiting and strict monetary/quantity validation at the gateway boundary.

Temporarily disable affected payment flows only where fraud or outage risk outweighs lost sales.

KEV status, EPSS and PoC availability are not provided; obtain them before assigning P1, while retaining heightened monitoring.

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