Critical Vulnerabilities Patched in WHMCS Billing Software for Hosting Providers

WebPros International has disclosed two serious vulnerabilities in its WHMCS billing management platform used by hosting and cloud service providers. CVE-2026-67399 allows unauthenticated remote code execution through unsafe deserialization of untrusted data under specific conditions, potentially compromising the entire server environment and associated data. CVE-2026-67398 affects the 2CheckOut payment gateway module and stems from missing authorization checks, enabling attackers to retrieve sensitive customer information including names, addresses, emails, and phone numbers without authentication. HackerOne assigned CVSS v4.0 scores of 9.3 (Critical) to the first issue and 8.2 (High) to the second. WebPros released fixed versions WHMCS 9.0.8 and 8.13.7, and recommended disabling the 2CheckOut module as a temporary mitigation for the second flaw.

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WebPros International has disclosed two serious vulnerabilities in its WHMCS billing management platform used by hosting and cloud service providers.

The first flaw, tracked as CVE-2026-67399, is caused by unsafe deserialization of untrusted data. Under specific conditions, it permits unauthenticated attackers to execute arbitrary code on the server, which could lead to full compromise of the installation and related customer data.

The second issue, CVE-2026-67398, affects the 2CheckOut payment gateway module. It results from missing authorization controls and allows unauthenticated access to personal customer details such as names, addresses, email addresses, and telephone numbers.

HackerOne rated CVE-2026-67399 with a CVSS v4.0 base score of 9.3 (Critical) and CVE-2026-67398 with a score of 8.2 (High).

WebPros has released patched versions WHMCS 9.0.8 and 8.13.7 that address both vulnerabilities. Administrators are urged to apply the updates immediately. For CVE-2026-67398, the company also advises temporarily disabling the 2CheckOut module as a workaround until the patch is installed.

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