The vulnerability identified as CVE-2026-16025 concerns improper validation of the specified quantity in input within the PayTR Virtual Pos iFrame API (v9x) WHMCS Module. This weakness, classified under CWE-1284, allows manipulation of input data, which can impact the availability of the affected system. The affected version is 9.0.0, with the issue resolved in versions after 9.0.0 but before 9.0.3. The CVSS v3.1 base score is 7.5, indicating a high severity with network attack vector, low attack complexity, no privileges required, no user interaction, unchanged scope, no confidentiality or integrity impact, but high impact on availability.

The vulnerability allows an attacker to manipulate input data related to the specified quantity, which can cause denial of service or other availability impacts on the PayTR Virtual Pos iFrame API (v9x) WHMCS Module. There is no impact on confidentiality or integrity according to the CVSS vector. No known exploits in the wild have been reported.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since no official fix or remediation level is provided, users should monitor vendor communications for updates and apply patches once available. Until then, consider restricting access to the affected module and validating inputs at the application level if possible.