FOSSBilling up to 0.7.x Unprotected Endpoint /api/guest/staff/create is_countable authentication bypass

Summaryinfo

A vulnerability categorized as critical has been discovered in FOSSBilling up to 0.7.x. Affected is the function is_countable of the file /api/guest/staff/create of the component Unprotected Endpoint. Executing a manipulation can lead to authentication bypass. This vulnerability is registered as CVE-2026-33543. It is possible to launch the attack remotely. No exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in FOSSBilling up to 0.7.x. It has been declared as critical. This vulnerability affects the function is_countable of the file /api/guest/staff/create of the component Unprotected Endpoint. The manipulation with an unknown input leads to a authentication bypass vulnerability. The CWE definition for the vulnerability is CWE-288. A product requires authentication, but the product has an alternate path or channel that does not require authentication. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

FOSSBilling is a free, open-source billing and client management system. Versions 0.7.2 and prior expose a guest API endpoint, /api/guest/staff/create, intended for initial administrator bootstrap. Due to a flawed admin-existence check, the endpoint remains usable after an administrator already exists. The flawed guard check uses is_countable() on a value that returns a Model_Admin object or null rather than a countable type, causing the expression to always evaluate as true and bypass the intended protection. As a result, an attacker can reach the unprotected endpoint to create a new administrator account and immediately authenticate, gaining a fully privileged admin session even when an admin already exists. This issue has been fixed in version 0.8.0.

The advisory is available at github.com. This vulnerability was named CVE-2026-33543 since 03/20/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit.

Upgrading to version 0.8.0 eliminates this vulnerability. The upgrade is hosted for download at github.com.

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Type

• Billing Software

Name

• FOSSBilling

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7

Website

• Product: https://github.com/FOSSBilling/FOSSBilling/

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